{"id":17202,"date":"2026-03-07T12:00:42","date_gmt":"2026-03-07T12:00:42","guid":{"rendered":"https:\/\/www.onlinelearningsystem.net\/xyz\/?page_id=17202"},"modified":"2026-10-10T23:32:45","modified_gmt":"2026-10-10T22:32:45","slug":"infrared-spectroscopy-a-level-chemistry","status":"publish","type":"page","link":"https:\/\/www.onlinelearningsystem.net\/xyz\/chemistry-blog\/infrared-spectroscopy-a-level-chemistry\/","title":{"rendered":"Infrared Spectroscopy"},"content":{"rendered":"\n\n<style>\n.olsb{--ink:#0e1d30;--muted:#4d5c6e;--line:#d6e1ec;--accent:#1f67b7;--card:#fff;\n  font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,\"Segoe UI\",sans-serif;color:var(--ink);\n  background:linear-gradient(180deg,#f8fbfe 0%,#eef4fa 100%)}\n.olsb *{box-sizing:border-box}\n.olsb .olsb-post{width:min(1180px,calc(100% - 40px));margin:0 auto;padding:56px 0 80px}\n.olsb 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(prefers-reduced-motion:reduce){.ols-b3d .b3d-seg button,.ols-b3d .b3d-pill{transition:none}}\n<\/style>\n\n<div class=\"olsb\">\n<main class=\"olsb-post\">\n  <header>\n    <p class=\"olsb-eyebrow\">Analytical Chemistry<\/p>\n    <h1 class=\"olsb-h1\">Infrared Spectroscopy<\/h1>\n    <p class=\"olsb-dek\">Infrared spectroscopy is one of the most powerful tools in modern chemistry, used to identify bonds, study molecular vibrations and even monitor greenhouse gases like CO\u2082 and methane. Discover how bond stretching, bending and dipole moments allow molecules to absorb infrared radiation and why this technique is essential for A-Level Chemistry.<\/p>\n  <\/header>\n\n  <section class=\"olsb-shell\" aria-label=\"Infrared Spectroscopy\">\n    <button class=\"olsb-zoom\" type=\"button\" aria-label=\"Open the image full screen\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infrared-spectroscopy-greenhouse-effect-illustration.png\" alt=\"Infrared spectroscopy used to study molecular vibrations and greenhouse gases like carbon dioxide and methane\"><\/button>\n  <\/section>\n\n  <section class=\"olsb-grid\">\n    <article class=\"olsb-article\">\n<div id=\"olsb-ols-info-section-ir-001\" class=\"ols-info-section ols-info-section-ir-001\">\n<style>\n.ols-info-section-ir-001 * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n\n.ols-info-section-ir-001 {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n\n.ols-info-section-ir-001 .ols-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n\n.ols-info-section-ir-001 .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n\n.ols-info-section-ir-001 .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 34px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n\n.ols-info-section-ir-001 .ols-line {\n  width: 80px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n\n.ols-info-section-ir-001 .ols-top-grid {\n  display: grid;\n  grid-template-columns: 1fr 1fr;\n  gap: 26px;\n  align-items: start;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-001 .ols-bottom-grid {\n  display: grid;\n  grid-template-columns: 1fr;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-001 .ols-text-card,\n.ols-info-section-ir-001 .ols-image-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n\n.ols-info-section-ir-001 .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0 0 18px 0;\n}\n\n.ols-info-section-ir-001 .ols-body:last-child { margin-bottom: 0; }\n\n.ols-info-section-ir-001 .ols-image-card { padding: 20px; }\n\n.ols-info-section-ir-001 .ols-image-card img {\n  width: 100%;\n  display: block;\n  border-radius: 14px;\n}\n\n.ols-info-section-ir-001 .ols-image-caption {\n  margin-top: 14px;\n  color: #1C244B;\n  font-size: 14px;\n  font-weight: 500;\n  line-height: 1.4;\n  text-align: center;\n}\n\n@media (max-width: 900px) {\n  .ols-info-section-ir-001 .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-001 .ols-title { font-size: 26px; }\n  .ols-info-section-ir-001 .ols-body { font-size: 16px; }\n  .ols-info-section-ir-001 .ols-top-grid { grid-template-columns: 1fr; }\n}\n\n@media (max-width: 480px) {\n  .ols-info-section-ir-001 .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-001 .ols-title { font-size: 22px; }\n  .ols-info-section-ir-001 .ols-body { font-size: 15px; }\n  .ols-info-section-ir-001 .ols-text-card,\n  .ols-info-section-ir-001 .ols-image-card { padding: 18px 16px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h2 class=\"ols-title\">Greenhouse Gases<\/h2>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-top-grid\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        Climate change affects the global environment and is strongly influenced by human activity. To limit atmospheric pollution, countries have created international agreements such as the Kyoto Protocol. These agreements aim to reduce emissions of major greenhouse gases including CO\u2082, methane (CH\u2084), nitrous oxide (N\u2082O), and ozone (O\u2083). Monitoring these gases is important for understanding their environmental impact.\n      <\/p>\n      <p class=\"ols-body\">\n        Measurements show that carbon dioxide levels in the atmosphere have increased significantly over the past 50 years. Data from ice cores indicate that before industrialisation, atmospheric CO\u2082 was about 278 ppm. Between 1000 and 1800, it varied by only about 7 ppm, showing that natural levels were relatively stable.\n      <\/p>\n    <\/div>\n\n    <div class=\"ols-image-card\">\n      <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infrared-spectroscopy-greenhouse-gases-diagram.png\"\n           alt=\"Infrared spectroscopy diagram showing greenhouse gases including carbon dioxide, methane, nitrous oxide and ozone\">\n      <div class=\"ols-image-caption\">\n        Greenhouse gases absorb infrared radiation at specific wavelengths, allowing their concentrations to be monitored.\n      <\/div>\n    <\/div>\n  <\/div>\n\n  <div class=\"ols-bottom-grid\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        However, between 1958 and 2004, atmospheric CO\u2082 increased from around 315 ppm to 378 ppm. Compared with the pre-industrial level of 278 ppm, this represents an increase of about 100 ppm, which is approximately 36% higher. This rise is largely linked to human activities such as burning fossil fuels and deforestation.\n      <\/p>\n      <p class=\"ols-body\">\n        Atmospheric gas concentrations are commonly measured using infrared spectroscopy, because greenhouse gases absorb infrared radiation at specific wavelengths. This allows scientists to detect and quantify the gases present in the atmosphere.\n      <\/p>\n    <\/div>\n  <\/div>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-002\" class=\"ols-info-section ols-info-section-ir-002\">\n<style>\n.ols-info-section-ir-002 * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n\n.ols-info-section-ir-002 {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n\n.ols-info-section-ir-002 .ols-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n\n.ols-info-section-ir-002 .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n\n.ols-info-section-ir-002 .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 34px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n\n.ols-info-section-ir-002 .ols-line {\n  width: 80px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n\n.ols-info-section-ir-002 .ols-top-grid {\n  display: grid;\n  grid-template-columns: 1fr 1fr;\n  gap: 26px;\n  align-items: start;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-002 .ols-bottom-grid {\n  display: grid;\n  grid-template-columns: 1fr;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-002 .ols-text-card,\n.ols-info-section-ir-002 .ols-image-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n\n.ols-info-section-ir-002 .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0 0 18px 0;\n}\n\n.ols-info-section-ir-002 .ols-body:last-child { margin-bottom: 0; }\n\n.ols-info-section-ir-002 .ols-body strong {\n  font-weight: 600;\n  color: #1C244B;\n}\n\n.ols-info-section-ir-002 .ols-body a {\n  color: #1C244B;\n  text-decoration: underline;\n  text-underline-offset: 3px;\n  text-decoration-thickness: 1px;\n}\n\n.ols-info-section-ir-002 .ols-image-card { padding: 20px; }\n\n.ols-info-section-ir-002 .ols-image-card img {\n  width: 100%;\n  display: block;\n  border-radius: 14px;\n}\n\n.ols-info-section-ir-002 .ols-image-caption {\n  margin-top: 14px;\n  color: #1C244B;\n  font-size: 14px;\n  font-weight: 500;\n  line-height: 1.4;\n  text-align: center;\n}\n\n@media (max-width: 900px) {\n  .ols-info-section-ir-002 .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-002 .ols-title { font-size: 26px; }\n  .ols-info-section-ir-002 .ols-body { font-size: 16px; }\n  .ols-info-section-ir-002 .ols-top-grid { grid-template-columns: 1fr; }\n}\n\n@media (max-width: 480px) {\n  .ols-info-section-ir-002 .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-002 .ols-title { font-size: 22px; }\n  .ols-info-section-ir-002 .ols-body { font-size: 15px; }\n  .ols-info-section-ir-002 .ols-text-card,\n  .ols-info-section-ir-002 .ols-image-card { padding: 18px 16px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h2 class=\"ols-title\">How Molecular Bond Vibrations Produce Infrared Absorption<\/h2>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-top-grid\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        Even when molecules are part of a solid structure, the atoms within them are not completely still. The bonds between atoms constantly vibrate, stretching and compressing while the molecule also bends slightly. Each of these vibrations happens at a specific frequency, which depends on the atoms involved in the bond and how they are connected.\n      <\/p>\n      <p class=\"ols-body\">\n        All molecules can absorb energy. When a molecule absorbs energy that matches the vibrational energy of one of its bonds, the vibration becomes stronger. In other words, the amplitude of the vibration increases and the bond enters what is called an excited state.\n      <\/p>\n    <\/div>\n\n    <div class=\"ols-image-card\">\n      <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infrared-spectroscopy-dipole-moment-diagram.png\"\n           alt=\"Infrared spectroscopy diagram showing molecular bond vibrations and changing dipole moment\">\n      <div class=\"ols-image-caption\">\n        Infrared absorption occurs when a bond vibration causes a change in dipole moment.\n      <\/div>\n    <\/div>\n  <\/div>\n\n  <div class=\"ols-bottom-grid\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        After a short time, the molecule returns to its <strong>ground state<\/strong> and releases the absorbed energy. This energy can be detected, and because each bond vibrates at its own characteristic frequency, the detected energy provides information about the types of bonds present in the molecule. These frequencies lie in the <strong>infrared region of the electromagnetic spectrum<\/strong>, which is why this technique is called <strong>infrared (IR) spectroscopy<\/strong>.\n      <\/p>\n      <p class=\"ols-body\">\n        Like other analytical techniques such as <a href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/chemistry-blog\/how-x-rays-reveal-the-structure-of-metal-crystals\/\" target=\"_blank\" rel=\"noopener\">X-ray diffraction<\/a>, infrared spectroscopy gives chemists a powerful way to investigate molecules and the bonds that hold them together.\n      <\/p>\n      <p class=\"ols-body\">\n        However, not every bond in a molecule will absorb infrared radiation. For absorption to occur, the vibration must cause a <strong>change in the dipole moment<\/strong> of the bond.\n      <\/p>\n      <p class=\"ols-body\">\n        A <strong>dipole moment<\/strong> exists when there is a separation of charge in a bond. It is defined as the <strong>magnitude of the charge multiplied by the distance between the charges<\/strong>. Many bonds have a dipole moment because the atoms involved have <strong>different electronegativities<\/strong>, meaning the electrons are shared unevenly. When these bonds vibrate, the dipole moment changes, allowing the bond to absorb infrared radiation.\n      <\/p>\n      <p class=\"ols-body\">\n        For a more detailed look at the underlying theory, you can explore this overview of <a href=\"https:\/\/chem.libretexts.org\/Courses\/Providence_College\/Organic_Chemistry_I\/05%3A_Analytical_Methods_for_Structure_Elucidation\/5.04%3A_Infrared_Spectroscopy\" target=\"_blank\" rel=\"noopener\">infrared spectroscopy from Chemistry LibreTexts<\/a>, which covers the same concepts at undergraduate level.\n      <\/p>\n    <\/div>\n  <\/div>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-003\" class=\"ols-info-section ols-info-section-ir-003\">\n<style>\n.ols-info-section-ir-003 * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n\n.ols-info-section-ir-003 {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n\n.ols-info-section-ir-003 .ols-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n\n.ols-info-section-ir-003 .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n\n.ols-info-section-ir-003 .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n\n.ols-info-section-ir-003 .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n\n.ols-info-section-ir-003 .ols-grid {\n  display: grid;\n  grid-template-columns: 1fr 1fr;\n  gap: 26px;\n  align-items: start;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-003 .ols-text-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n\n.ols-info-section-ir-003 .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0 0 18px 0;\n}\n\n.ols-info-section-ir-003 .ols-body:last-child { margin-bottom: 0; }\n\n.ols-info-section-ir-003 .ols-body strong {\n  font-weight: 600;\n  color: #1C244B;\n}\n\n.ols-info-section-ir-003 ul {\n  margin: 10px 0 18px 18px;\n  color: #374151;\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.8;\n}\n\n@media (max-width: 900px) {\n  .ols-info-section-ir-003 .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-003 .ols-title { font-size: 24px; }\n  .ols-info-section-ir-003 .ols-body,\n  .ols-info-section-ir-003 ul { font-size: 16px; }\n  .ols-info-section-ir-003 .ols-grid { grid-template-columns: 1fr; }\n}\n\n@media (max-width: 480px) {\n  .ols-info-section-ir-003 .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-003 .ols-title { font-size: 20px; }\n  .ols-info-section-ir-003 .ols-body,\n  .ols-info-section-ir-003 ul { font-size: 15px; }\n  .ols-info-section-ir-003 .ols-text-card { padding: 18px 16px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">When Bonds Absorb Infrared Radiation<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-grid\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        Not all molecules absorb infrared radiation. In symmetrical molecules, there may be no overall dipole moment. This can happen if there is no separation of charge, such as in diatomic molecules made from the same element, or when the dipole moments of individual bonds cancel each other out. When this occurs, infrared radiation is not absorbed.\n      <\/p>\n      <p class=\"ols-body\">\n        However, when bonds stretch or bend, the dipole moment of the molecule can change. If this change occurs during the vibration, the bond is able to absorb infrared radiation.\n      <\/p>\n      <p class=\"ols-body\">\n        Some bonds produce strong infrared absorptions, particularly polar bonds such as C\u2013O, C=O and O\u2013H. These bonds have significant differences in electronegativity between the atoms, so their dipole moments change noticeably during vibration. In contrast, non-polar bonds such as C\u2013C and C=C usually produce much weaker absorptions.\n      <\/p>\n    <\/div>\n\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        There are two main types of molecular vibration:\n      <\/p>\n      <ul>\n        <li>Stretching vibrations, where the bond length increases and decreases.<\/li>\n        <li>Bending vibrations, where the bond angle changes.<\/li>\n      <\/ul>\n      <p class=\"ols-body\">\n        Bending vibrations require less energy than stretching vibrations, so they occur at lower energy and longer wavelengths in the infrared region.\n      <\/p>\n      <p class=\"ols-body\">\n        In planar molecules, such as sulphur dioxide (SO\u2082) and carbon dioxide (CO\u2082), infrared radiation can be absorbed through either bond stretching or bond bending vibrations.\n      <\/p>\n    <\/div>\n  <\/div>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-005-a\" class=\"ols-info-section ols-info-section-ir-005-a\">\n<style>\n.ols-info-section-ir-005-a * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n\n.ols-info-section-ir-005-a {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n\n.ols-info-section-ir-005-a .ols-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n\n.ols-info-section-ir-005-a .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n\n.ols-info-section-ir-005-a .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n\n.ols-info-section-ir-005-a .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n\n.ols-info-section-ir-005-a .ols-stack {\n  display: flex;\n  flex-direction: column;\n  gap: 22px;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-005-a .ols-text-card,\n.ols-info-section-ir-005-a .ols-image-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n\n.ols-info-section-ir-005-a .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0;\n}\n\n.ols-info-section-ir-005-a .ols-image-card img {\n  width: 100%;\n  display: block;\n  border-radius: 14px;\n}\n\n@media (max-width: 900px) {\n  .ols-info-section-ir-005-a .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-005-a .ols-title { font-size: 24px; }\n  .ols-info-section-ir-005-a .ols-body { font-size: 16px; }\n}\n\n@media (max-width: 480px) {\n  .ols-info-section-ir-005-a .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-005-a .ols-title { font-size: 20px; }\n  .ols-info-section-ir-005-a .ols-body { font-size: 15px; }\n  .ols-info-section-ir-005-a .ols-text-card,\n  .ols-info-section-ir-005-a .ols-image-card { padding: 18px 16px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">Sulphur Dioxide (SO\u2082)<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-stack\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        Each type of molecular vibration can cause a change in the dipole moment of the molecule. When this happens, the molecule is able to absorb infrared radiation at the frequency corresponding to that vibration. Because different vibrational motions occur at different energies, each one produces a separate absorption in the infrared spectrum.\n      <\/p>\n      <p class=\"ols-body\">\n        As a result, a molecule can show multiple absorption peaks, with each peak representing a specific type of bond vibration. For example, sulphur dioxide (SO\u2082) has three possible vibrational motions. Since each of these vibrations changes the dipole moment, all three absorb infrared radiation.\n      <\/p>\n      <p class=\"ols-body\">\n        This means the infrared spectrum of sulphur dioxide shows three distinct absorption peaks, each corresponding to one of its vibrational modes.\n      <\/p>\n    <\/div>\n\n    <div class=\"ols-image-card\">\n      <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infraredspectrumso2.png\"\n           alt=\"Infrared spectrum of sulphur dioxide showing three absorption peaks corresponding to different vibrational modes\">\n    <\/div>\n  <\/div>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-004\" class=\"ols-info-section ols-info-section-ir-004\">\n<style>\n.ols-info-section-ir-004 * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n.ols-info-section-ir-004 {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n.ols-info-section-ir-004 .ols-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n.ols-info-section-ir-004 .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-radius: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n.ols-info-section-ir-004 .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n.ols-info-section-ir-004 .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n.ols-info-section-ir-004 .ols-text-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n.ols-info-section-ir-004 .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0;\n}\n.ols-info-section-ir-004 .ols-viewer-wrap {\n  margin-top: 28px;\n  border-radius: 18px;\n  overflow: hidden;\n  border: 1px solid #e5e7eb;\n}\n.ols-info-section-ir-004 .ols-viewer-inner {\n  width: 100%;\n  height: 420px;\n  background: #0e1120;\n  position: relative;\n}\n.ols-info-section-ir-004 .ols-viewer-inner canvas {\n  display: block;\n  width: 100% !important;\n  height: 100% !important;\n  cursor: grab;\n  touch-action: none;\n}\n.ols-info-section-ir-004 .ols-viewer-controls {\n  background: #f9fafb;\n  border-top: 1px solid #e5e7eb;\n  padding: 18px 20px 14px;\n}\n.ols-info-section-ir-004 .ols-viewer-buttons {\n  display: flex;\n  flex-wrap: wrap;\n  gap: 10px;\n  justify-content: center;\n  margin-bottom: 14px;\n}\n.ols-info-section-ir-004 .ols-vbtn {\n  border: none;\n  border-radius: 999px;\n  padding: 10px 20px;\n  background: #1C244B;\n  color: #fff;\n  font-size: 14px;\n  font-family: Poppins, Arial, sans-serif;\n  font-weight: 500;\n  cursor: pointer;\n  transition: background 0.2s, transform 0.15s;\n}\n.ols-info-section-ir-004 .ols-vbtn:hover { transform: translateY(-2px); }\n.ols-info-section-ir-004 .ols-vbtn-secondary { background: #374151; }\n.ols-info-section-ir-004 .ols-vbtn-active { background: #3B4FD4; }\n.ols-info-section-ir-004 .ols-caption {\n  text-align: center;\n  color: #6b7280;\n  font-size: 14px;\n  font-style: italic;\n  margin: 0;\n  min-height: 20px;\n}\n@media (max-width: 900px) {\n  .ols-info-section-ir-004 .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-004 .ols-title { font-size: 24px; }\n  .ols-info-section-ir-004 .ols-body { font-size: 16px; }\n  .ols-info-section-ir-004 .ols-viewer-inner { height: 340px; }\n}\n@media (max-width: 480px) {\n  .ols-info-section-ir-004 .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-004 .ols-title { font-size: 20px; }\n  .ols-info-section-ir-004 .ols-body { font-size: 15px; }\n  .ols-info-section-ir-004 .ols-text-card { padding: 18px 16px; }\n  .ols-info-section-ir-004 .ols-viewer-inner { height: 280px; }\n  .ols-info-section-ir-004 .ols-vbtn { font-size: 13px; padding: 9px 14px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">Sulphur Dioxide (SO&#8322;)<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-text-card\">\n    <p class=\"ols-body\">\n      Sulphur dioxide has three different possible vibrations, each occurring at a different infrared frequency.\n    <\/p>\n  <\/div>\n\n  <!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. All rights reserved. -->\n<section class=\"ols-b3d\" data-b3d=\"so2-vib\" id=\"b3d-so2-vib\">\n<div class=\"b3d-head\"><h3 class=\"b3d-title\">Sulphur dioxide: three vibrations<\/h3><p class=\"b3d-sub\">Choose a vibration to watch the atoms move. Every one of them changes the dipole moment, so SO\u2082 shows three infrared peaks.<\/p><\/div>\n<div class=\"b3d-stage\" data-b3d-stage><canvas class=\"b3d-canvas\" aria-label=\"Sulphur dioxide: three vibrations: interactive 3D model, drag to rotate\"><\/canvas>\n<div class=\"b3d-caption\" data-b3d-caption aria-live=\"polite\"><\/div>\n<div class=\"b3d-hint\">Drag to rotate<\/div>\n<div class=\"b3d-badges\" data-b3d-badges><\/div>\n<\/div><div class=\"b3d-controls\">\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">Vibration<\/span><div class=\"b3d-seg\" role=\"group\" aria-label=\"Vibration\">\n<button type=\"button\" data-b3d-mode=\"sym\" aria-pressed=\"true\"><span class=\"b3d-n\">1<\/span>Symmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"asym\" aria-pressed=\"false\"><span class=\"b3d-n\">2<\/span>Asymmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"bend\" aria-pressed=\"false\"><span class=\"b3d-n\">3<\/span>Bending<\/button>\n<\/div><\/div>\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">View<\/span><button type=\"button\" class=\"b3d-pill\" data-b3d-pause aria-pressed=\"false\">Pause<\/button><button type=\"button\" class=\"b3d-pill\" data-b3d-reset>Reset view<\/button><\/div><\/div>\n<div class=\"b3d-info\"><h4>Why all three absorb infrared<\/h4><p>SO\u2082 is bent, so its S\u2013O bond dipoles do not cancel. Stretching or bending changes the size of the overall dipole, and a vibration that changes the dipole moment absorbs infrared radiation.<\/p>\n<div class=\"b3d-facts\"><div class=\"b3d-fact\"><span>Shape<\/span><strong>Bent, about 119\u00b0<\/strong><\/div><div class=\"b3d-fact\"><span>Vibrations<\/span><strong>3<\/strong><\/div><div class=\"b3d-fact\"><span>Infrared active<\/span><strong>All 3<\/strong><\/div><\/div>\n<div class=\"b3d-key\"><span><i style=\"background:#e7b416\"><\/i>Sulphur<\/span><span><i style=\"background:#d8342c\"><\/i>Oxygen<\/span><span><i class=\"k-arrow\"><\/i>Direction the atom is moving<\/span><\/div>\n<\/div>\n<\/section>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-006-a\" class=\"ols-info-section ols-info-section-ir-006-a\">\n<style>\n.ols-info-section-ir-006-a * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n\n.ols-info-section-ir-006-a {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n\n.ols-info-section-ir-006-a .ols-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n\n.ols-info-section-ir-006-a .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n\n.ols-info-section-ir-006-a .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n\n.ols-info-section-ir-006-a .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n\n.ols-info-section-ir-006-a .ols-stack {\n  display: flex;\n  flex-direction: column;\n  gap: 22px;\n  margin-top: 26px;\n}\n\n.ols-info-section-ir-006-a .ols-text-card,\n.ols-info-section-ir-006-a .ols-image-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n\n.ols-info-section-ir-006-a .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0;\n}\n\n.ols-info-section-ir-006-a .ols-image-card img {\n  width: 100%;\n  display: block;\n  border-radius: 14px;\n}\n\n@media (max-width: 900px) {\n  .ols-info-section-ir-006-a .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-006-a .ols-title { font-size: 24px; }\n  .ols-info-section-ir-006-a .ols-body { font-size: 16px; }\n}\n\n@media (max-width: 480px) {\n  .ols-info-section-ir-006-a .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-006-a .ols-title { font-size: 20px; }\n  .ols-info-section-ir-006-a .ols-body { font-size: 15px; }\n  .ols-info-section-ir-006-a .ols-text-card,\n  .ols-info-section-ir-006-a .ols-image-card { padding: 18px 16px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">Carbon dioxide (CO\u2082)<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-stack\">\n    <div class=\"ols-text-card\">\n      <p class=\"ols-body\">\n        Consequently, the infrared spectrum of carbon dioxide shows absorptions only for asymmetrical stretching and bending vibrations, while symmetrical stretching is not detected.\n      <\/p>\n    <\/div>\n\n    <div class=\"ols-image-card\">\n      <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infrared-spectroscopy-carbon-dioxide-spectrum.png\"\n           alt=\"Infrared spectrum of carbon dioxide showing absorption peaks for asymmetrical stretching and bending vibrations\">\n    <\/div>\n  <\/div>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-005-b\" class=\"ols-info-section ols-info-section-ir-005-b\">\n<style>\n.ols-info-section-ir-005-b * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n.ols-info-section-ir-005-b {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n.ols-info-section-ir-005-b .ols-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n.ols-info-section-ir-005-b .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n.ols-info-section-ir-005-b .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n.ols-info-section-ir-005-b .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n.ols-info-section-ir-005-b .ols-text-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n.ols-info-section-ir-005-b .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0 0 14px 0;\n}\n.ols-info-section-ir-005-b .ols-body:last-child { margin-bottom: 0; }\n.ols-info-section-ir-005-b .ols-body strong {\n  font-weight: 600;\n  color: #1C244B;\n}\n.ols-info-section-ir-005-b .ols-viewer-wrap {\n  margin-top: 28px;\n  border-radius: 18px;\n  overflow: hidden;\n  border: 1px solid #e5e7eb;\n}\n.ols-info-section-ir-005-b .ols-viewer-inner {\n  width: 100%;\n  height: 420px;\n  background: #0e1120;\n  position: relative;\n}\n.ols-info-section-ir-005-b .ols-viewer-inner canvas {\n  display: block;\n  width: 100% !important;\n  height: 100% !important;\n  cursor: grab;\n  touch-action: none;\n}\n.ols-info-section-ir-005-b .ols-viewer-controls {\n  background: #f9fafb;\n  border-top: 1px solid #e5e7eb;\n  padding: 18px 20px 14px;\n}\n.ols-info-section-ir-005-b .ols-viewer-buttons {\n  display: flex;\n  flex-wrap: wrap;\n  gap: 10px;\n  justify-content: center;\n  margin-bottom: 14px;\n}\n.ols-info-section-ir-005-b .ols-vbtn {\n  border: none;\n  border-radius: 999px;\n  padding: 10px 20px;\n  background: #1C244B;\n  color: #fff;\n  font-size: 14px;\n  font-family: Poppins, Arial, sans-serif;\n  font-weight: 500;\n  cursor: pointer;\n  transition: background 0.2s, transform 0.15s;\n}\n.ols-info-section-ir-005-b .ols-vbtn:hover { transform: translateY(-2px); }\n.ols-info-section-ir-005-b .ols-vbtn-secondary { background: #374151; }\n.ols-info-section-ir-005-b .ols-vbtn-active { background: #3B4FD4; }\n.ols-info-section-ir-005-b .ols-caption {\n  text-align: center;\n  color: #6b7280;\n  font-size: 14px;\n  font-style: italic;\n  margin: 0;\n  min-height: 20px;\n}\n@media (max-width: 900px) {\n  .ols-info-section-ir-005-b .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-005-b .ols-title { font-size: 24px; }\n  .ols-info-section-ir-005-b .ols-body { font-size: 16px; }\n  .ols-info-section-ir-005-b .ols-viewer-inner { height: 340px; }\n}\n@media (max-width: 480px) {\n  .ols-info-section-ir-005-b .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-005-b .ols-title { font-size: 20px; }\n  .ols-info-section-ir-005-b .ols-body { font-size: 15px; }\n  .ols-info-section-ir-005-b .ols-text-card { padding: 18px 16px; }\n  .ols-info-section-ir-005-b .ols-viewer-inner { height: 280px; }\n  .ols-info-section-ir-005-b .ols-vbtn { font-size: 13px; padding: 9px 14px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">Carbon Dioxide (CO&#8322;)<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-text-card\">\n    <p class=\"ols-body\">\n      Carbon dioxide (CO&#8322;) is a <strong>linear molecule<\/strong>, meaning its atoms lie in a straight line. Because of this symmetry, some vibrations do not cause a change in the dipole moment of the molecule.\n    <\/p>\n    <p class=\"ols-body\">\n      During <strong>symmetrical stretching<\/strong>, both C=O bonds stretch and compress at the same time. The effect on one side of the molecule is balanced by the identical effect on the other side. As a result, there is no overall change in dipole moment, so this vibration does <strong>not<\/strong> absorb infrared radiation.\n    <\/p>\n    <p class=\"ols-body\">\n      However, <strong>asymmetrical stretching<\/strong> (where one bond stretches while the other compresses) and <strong>bond bending<\/strong> both create a temporary imbalance in charge distribution. Because the dipole moment changes during these vibrations, they <strong>do<\/strong> absorb infrared radiation.\n    <\/p>\n  <\/div>\n\n  <!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. All rights reserved. -->\n<section class=\"ols-b3d\" data-b3d=\"co2-vib\" id=\"b3d-co2-vib\">\n<div class=\"b3d-head\"><h3 class=\"b3d-title\">Carbon dioxide: which vibrations absorb?<\/h3><p class=\"b3d-sub\">Choose a vibration. The badge says whether it changes the dipole moment, and so whether it absorbs infrared radiation.<\/p><\/div>\n<div class=\"b3d-stage\" data-b3d-stage><canvas class=\"b3d-canvas\" aria-label=\"Carbon dioxide: which vibrations absorb?: interactive 3D model, drag to rotate\"><\/canvas>\n<div class=\"b3d-caption\" data-b3d-caption aria-live=\"polite\"><\/div>\n<div class=\"b3d-hint\">Drag to rotate<\/div>\n<div class=\"b3d-badges\" data-b3d-badges><\/div>\n<\/div><div class=\"b3d-controls\">\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">Vibration<\/span><div class=\"b3d-seg\" role=\"group\" aria-label=\"Vibration\">\n<button type=\"button\" data-b3d-mode=\"sym\" aria-pressed=\"true\"><span class=\"b3d-n\">1<\/span>Symmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"asym\" aria-pressed=\"false\"><span class=\"b3d-n\">2<\/span>Asymmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"bend\" aria-pressed=\"false\"><span class=\"b3d-n\">3<\/span>Bending<\/button>\n<\/div><\/div>\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">View<\/span><button type=\"button\" class=\"b3d-pill\" data-b3d-pause aria-pressed=\"false\">Pause<\/button><button type=\"button\" class=\"b3d-pill\" data-b3d-reset>Reset view<\/button><\/div><\/div>\n<div class=\"b3d-info\"><h4>Symmetry decides<\/h4><p>CO\u2082 is linear, so in the symmetric stretch the two C=O dipoles stay equal and opposite and the molecule never has a dipole: no absorption. The asymmetric stretch and the bend both create a dipole, so they absorb.<\/p>\n<div class=\"b3d-facts\"><div class=\"b3d-fact\"><span>Shape<\/span><strong>Linear, 180\u00b0<\/strong><\/div><div class=\"b3d-fact\"><span>Infrared active<\/span><strong>Asymmetric stretch, bending<\/strong><\/div><div class=\"b3d-fact\"><span>Infrared inactive<\/span><strong>Symmetric stretch<\/strong><\/div><\/div>\n<div class=\"b3d-key\"><span><i style=\"background:#464a54\"><\/i>Carbon<\/span><span><i style=\"background:#d8342c\"><\/i>Oxygen<\/span><span><i class=\"k-arrow\"><\/i>Direction the atom is moving<\/span><\/div>\n<\/div>\n<\/section>\n<\/div>\n<\/div>\n\n<div id=\"olsb-ols-info-section-ir-006-b\" class=\"ols-info-section ols-info-section-ir-006-b\">\n<style>\n.ols-info-section-ir-006-b * {\n  box-sizing: border-box;\n  font-family: Poppins, Arial, sans-serif;\n}\n.ols-info-section-ir-006-b {\n  max-width: 1100px;\n  margin: 0 auto 48px auto;\n  padding: 0 16px;\n}\n.ols-info-section-ir-006-b .ols-card {\n  background: #ffffff;\n  border: 1px solid #e5e7eb;\n  border-radius: 24px;\n  padding: 36px 40px;\n  box-shadow: 0 7px 18px rgba(0,0,0,0.07);\n}\n.ols-info-section-ir-006-b .ols-pill {\n  display: inline-block;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-weight: 500;\n  letter-spacing: 0.04em;\n  border-radius: 999px;\n  padding: 6px 14px;\n  margin: 0 0 20px 0;\n}\n.ols-info-section-ir-006-b .ols-title {\n  margin: 0 0 8px 0;\n  font-size: 30px;\n  font-weight: 600;\n  line-height: 1.2;\n  color: #1C244B;\n  text-shadow: -9px 0 9px rgba(28,36,75,0.3);\n}\n.ols-info-section-ir-006-b .ols-line {\n  width: 70px;\n  height: 4px;\n  background: #c81e1e;\n  border-radius: 999px;\n  margin: 0 0 24px 0;\n}\n.ols-info-section-ir-006-b .ols-text-card {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n}\n.ols-info-section-ir-006-b .ols-body {\n  font-size: 18px;\n  font-weight: 300;\n  line-height: 1.9;\n  color: #374151;\n  margin: 0 0 14px 0;\n}\n.ols-info-section-ir-006-b .ols-body:last-child { margin-bottom: 0; }\n.ols-info-section-ir-006-b .ols-body strong { font-weight: 600; color: #1C244B; }\n.ols-info-section-ir-006-b .ols-body a {\n  color: #1C244B;\n  text-decoration: underline;\n  text-underline-offset: 2px;\n  text-decoration-thickness: 1px;\n}\n.ols-info-section-ir-006-b .ols-body a:hover { opacity: 0.75; }\n.ols-info-section-ir-006-b .ols-viewer-wrap {\n  margin-top: 28px;\n  border-radius: 18px;\n  overflow: hidden;\n  border: 1px solid #e5e7eb;\n}\n.ols-info-section-ir-006-b .ols-viewer-inner {\n  width: 100%;\n  height: 440px;\n  background: #0e1120;\n  position: relative;\n}\n.ols-info-section-ir-006-b .ols-viewer-inner canvas {\n  display: block;\n  width: 100% !important;\n  height: 100% !important;\n  cursor: grab;\n  touch-action: none;\n}\n.ols-info-section-ir-006-b .ols-viewer-controls {\n  background: #f9fafb;\n  border-top: 1px solid #e5e7eb;\n  padding: 18px 20px 14px;\n}\n.ols-info-section-ir-006-b .ols-viewer-buttons {\n  display: flex;\n  flex-wrap: wrap;\n  gap: 10px;\n  justify-content: center;\n  margin-bottom: 14px;\n}\n.ols-info-section-ir-006-b .ols-vbtn {\n  border: none;\n  border-radius: 999px;\n  padding: 10px 18px;\n  background: #1C244B;\n  color: #fff;\n  font-size: 13px;\n  font-family: Poppins, Arial, sans-serif;\n  font-weight: 500;\n  cursor: pointer;\n  transition: background 0.2s, transform 0.15s;\n}\n.ols-info-section-ir-006-b .ols-vbtn:hover { transform: translateY(-2px); }\n.ols-info-section-ir-006-b .ols-vbtn-secondary { background: #374151; }\n.ols-info-section-ir-006-b .ols-vbtn-active { background: #3B4FD4; }\n.ols-info-section-ir-006-b .ols-caption {\n  text-align: center;\n  color: #6b7280;\n  font-size: 14px;\n  font-style: italic;\n  margin: 0;\n  min-height: 20px;\n}\n.ols-info-section-ir-006-b .ols-text-card-below {\n  background: #F3F4F6;\n  border: 1px solid #e5e7eb;\n  border-radius: 18px;\n  padding: 22px 24px;\n  box-shadow: 0 4px 14px rgba(0,0,0,0.06);\n  margin-top: 28px;\n}\n@media (max-width: 900px) {\n  .ols-info-section-ir-006-b .ols-card { padding: 24px 20px; }\n  .ols-info-section-ir-006-b .ols-title { font-size: 24px; }\n  .ols-info-section-ir-006-b .ols-body { font-size: 16px; }\n  .ols-info-section-ir-006-b .ols-viewer-inner { height: 360px; }\n}\n@media (max-width: 480px) {\n  .ols-info-section-ir-006-b .ols-card { padding: 20px 16px; }\n  .ols-info-section-ir-006-b .ols-title { font-size: 20px; }\n  .ols-info-section-ir-006-b .ols-body { font-size: 15px; }\n  .ols-info-section-ir-006-b .ols-text-card { padding: 18px 16px; }\n  .ols-info-section-ir-006-b .ols-text-card-below { padding: 18px 16px; }\n  .ols-info-section-ir-006-b .ols-viewer-inner { height: 300px; }\n  .ols-info-section-ir-006-b .ols-vbtn { font-size: 12px; padding: 8px 12px; }\n}\n<\/style>\n\n<div class=\"ols-card\">\n  <span class=\"ols-pill\">Infrared Spectroscopy<\/span>\n  <h3 class=\"ols-title\">Vibrations in Larger Molecules<\/h3>\n  <div class=\"ols-line\"><\/div>\n\n  <div class=\"ols-text-card\">\n    <p class=\"ols-body\">\n      As molecules become larger and more complex, the number of possible vibrational modes increases. Different parts of the molecule can move in different ways, including <strong>stretching<\/strong>, <strong>bending<\/strong>, <strong>twisting<\/strong>, and <strong>rocking<\/strong> motions.\n    <\/p>\n    <p class=\"ols-body\">\n      Each of these vibrations occurs at a specific frequency and produces its own absorption in the infrared spectrum. This means that larger molecules typically show many absorption peaks, with each peak corresponding to a particular type of molecular vibration.\n    <\/p>\n    <p class=\"ols-body\">\n      Although the number of peaks increases with molecular size, certain types of bonds absorb infrared radiation in predictable regions of the spectrum. For example, bonds such as <strong>O&#8211;H<\/strong>, <strong>C=O<\/strong>, and <strong>C&#8211;H<\/strong> absorb at characteristic frequencies regardless of the rest of the molecule.\n    <\/p>\n  <\/div>\n\n  <!-- Copyright (c) 2026 Dr. Mohammed Al-Fatah, onlinelearningsystem.net. All rights reserved. -->\n<section class=\"ols-b3d\" data-b3d=\"ch2-vib\" id=\"b3d-ch2-vib\">\n<div class=\"b3d-head\"><h3 class=\"b3d-title\">Six ways a CH\u2082 group vibrates<\/h3><p class=\"b3d-sub\">In a larger molecule each \u2013CH\u2082\u2013 group can stretch and bend in several ways. Choose one to watch it on a CH\u2082 group in a carbon chain.<\/p><\/div>\n<div class=\"b3d-stage\" data-b3d-stage><canvas class=\"b3d-canvas\" aria-label=\"Six ways a CH\u2082 group vibrates: interactive 3D model, drag to rotate\"><\/canvas>\n<div class=\"b3d-caption\" data-b3d-caption aria-live=\"polite\"><\/div>\n<div class=\"b3d-hint\">Drag to rotate<\/div>\n<\/div><div class=\"b3d-controls\">\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">Vibration<\/span><div class=\"b3d-seg\" role=\"group\" aria-label=\"Vibration\">\n<button type=\"button\" data-b3d-mode=\"sstr\" aria-pressed=\"true\"><span class=\"b3d-n\">1<\/span>Symmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"astr\" aria-pressed=\"false\"><span class=\"b3d-n\">2<\/span>Asymmetric stretch<\/button>\n<button type=\"button\" data-b3d-mode=\"sci\" aria-pressed=\"false\"><span class=\"b3d-n\">3<\/span>Scissoring<\/button>\n<button type=\"button\" data-b3d-mode=\"rock\" aria-pressed=\"false\"><span class=\"b3d-n\">4<\/span>Rocking<\/button>\n<button type=\"button\" data-b3d-mode=\"wag\" aria-pressed=\"false\"><span class=\"b3d-n\">5<\/span>Wagging<\/button>\n<button type=\"button\" data-b3d-mode=\"twist\" aria-pressed=\"false\"><span class=\"b3d-n\">6<\/span>Twisting<\/button>\n<\/div><\/div>\n<div class=\"b3d-row\"><span class=\"b3d-rowlab\">View<\/span><button type=\"button\" class=\"b3d-pill\" data-b3d-pause aria-pressed=\"false\">Pause<\/button><button type=\"button\" class=\"b3d-pill\" data-b3d-reset>Reset view<\/button><\/div><\/div>\n<div class=\"b3d-info\"><h4>More atoms, more peaks<\/h4><p>Each kind of motion has its own frequency, so larger molecules show many peaks. Stretches of C\u2013H bonds absorb at higher wavenumbers than the bending motions, which is why the C\u2013H stretch is easy to spot.<\/p>\n<div class=\"b3d-facts\"><div class=\"b3d-fact\"><span>C\u2013H stretch<\/span><strong>2850\u20132950 cm\u207b\u00b9<\/strong><\/div><div class=\"b3d-fact\"><span>CH\u2082 scissoring<\/span><strong>about 1465 cm\u207b\u00b9<\/strong><\/div><div class=\"b3d-fact\"><span>Motions shown<\/span><strong>2 stretches, 4 bends<\/strong><\/div><\/div>\n<div class=\"b3d-key\"><span><i style=\"background:#464a54\"><\/i>Carbon<\/span><span><i style=\"background:#f4f5f8\"><\/i>Hydrogen<\/span><span><i style=\"background:rgba(70,74,84,0.35)\"><\/i>Rest of the carbon chain<\/span><span><i class=\"k-arrow\"><\/i>Direction the atom is moving<\/span><\/div>\n<\/div>\n<\/section>\n\n  <div class=\"ols-text-card-below\">\n    <p class=\"ols-body\">\n      Because of this, infrared spectroscopy is extremely useful for <strong>identifying functional groups within molecules<\/strong>. By analysing the positions of absorption peaks in the infrared spectrum, chemists can determine which types of bonds &mdash; and therefore which <strong>functional groups<\/strong> &mdash; are present in a compound.\n    <\/p>\n    <p class=\"ols-body\">\n      You can read more about how chemists use this technique in the classroom in this <a href=\"https:\/\/edu.rsc.org\/resources\/infrared-ir-spectroscopy\/4010243.article\" target=\"_blank\" rel=\"noopener\">infrared spectroscopy resource from the Royal Society of Chemistry<\/a>.\n    <\/p>\n  <\/div>\n<\/div>\n<\/div>\n\n<!-- ============================================================\n     SHARED THREE.JS LOADER + ALL THREE INTERACTIVE VIEWERS\n     (Single shared loader so three.min.js is loaded only once.)\n============================================================ -->\n\n    <\/article>\n    <aside class=\"olsb-side\">\n      <h3>In this article<\/h3>\n      <ul class=\"olsb-toc\"><li><a href=\"#olsb-ols-info-section-ir-001\">Greenhouse Gases<\/a><\/li><li><a href=\"#olsb-ols-info-section-ir-002\">How Molecular Bond Vibrations Produce Infrared Absorption<\/a><\/li><li><a href=\"#olsb-ols-info-section-ir-003\">When Bonds Absorb Infrared Radiation<\/a><\/li><li><a href=\"#olsb-ols-info-section-ir-005-a\">Sulphur Dioxide (SO\u2082)<\/a><\/li><li><a href=\"#olsb-ols-info-section-ir-006-a\">Carbon dioxide (CO\u2082)<\/a><\/li><li><a href=\"#olsb-ols-info-section-ir-006-b\">Vibrations in Larger Molecules<\/a><\/li><\/ul>\n      <div class=\"olsb-promo\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/04\/edexcel-international-a-level-chemistry-topic-2-atomic-structure-periodic-table-course-banner.jpg\" alt=\"A-Level Chemistry course on covalent bonding, molecular shapes and symmetry of molecules\" loading=\"lazy\"><strong>A Level Chemistry Course<\/strong><h4>Master Molecular Shapes &amp; Covalent Bonding<\/h4><p>Take your understanding further with our complete A-Level Chemistry course on covalent bonding, molecular geometry and the symmetry of molecules.<\/p><a class=\"olsb-btn\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/product\/covalent-bonding-shapes-of-molecules-edexcel-t3b-c\/\">Explore the Course<\/a><\/div>\n    <\/aside>\n  <\/section>\n\n  <section class=\"olsb-more\" aria-label=\"Keep reading\">\n    <h2>Keep reading<\/h2>\n    <div class=\"olsb-reads\"><a class=\"olsb-read-card\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/chemistry-blog\/how-x-rays-reveal-the-structure-of-metal-crystals\/\"><span class=\"olsb-read-img\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/ChatGPT-Image-Mar-8-2026-05_43_16-PM.jpg\" alt=\"How X-Rays Reveal the Structure of Metal Crystals\" loading=\"lazy\"><\/span><span class=\"olsb-read-body\"><span class=\"olsb-read-label\">Crystal Structures<\/span><strong>How X-Rays Reveal the Structure of Metal Crystals<\/strong><span class=\"olsb-read-desc\">X-ray diffraction, face-centred and body-centred cubic lattices in 3D, and extension questions on the shapes of sulphur compounds.<\/span><span class=\"olsb-read-more\">Read article &rarr;<\/span><\/span><\/a><a class=\"olsb-read-card\" href=\"https:\/\/www.onlinelearningsystem.net\/xyz\/chemistry-blog\/football-materials-science\/\"><span class=\"olsb-read-img\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/06\/football.jpg\" alt=\"The Science Inside a World Cup Football infographic\" loading=\"lazy\"><\/span><span class=\"olsb-read-body\"><span class=\"olsb-read-label\">Sports Engineering<\/span><strong>The Science Inside a World Cup Football<\/strong><span class=\"olsb-read-desc\">Explore the layered materials inside a professional football and how modern engineering shapes touch, flight, bounce and durability.<\/span><span class=\"olsb-read-more\">Read article &rarr;<\/span><\/span><\/a><a class=\"olsb-read-card\" href=\"https:\/\/www.a-levelchemistry.co.uk\/development-of-the-modern-atomic-model.html\" target=\"_blank\" rel=\"noopener\"><span class=\"olsb-read-img\"><img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/05\/Erwin-Schrodinger.webp\" alt=\"Erwin Schrodinger and the development of the modern atomic model\" loading=\"lazy\"><\/span><span class=\"olsb-read-body\"><span class=\"olsb-read-label\">Atomic Structure<\/span><strong>Development of the Modern Atomic Model<\/strong><span class=\"olsb-read-desc\">From Dalton\u2019s solid spheres to Schrodinger\u2019s quantum mechanical model: how Thomson, Rutherford, Bohr and Schrodinger changed our picture of the atom.<\/span><span class=\"olsb-read-more\">Read on a-levelchemistry.co.uk &rarr;<\/span><\/span><\/a><\/div>\n  <\/section>\n<\/main>\n<\/div>\n\n<div class=\"olsb-lightbox\" aria-hidden=\"true\" role=\"dialog\" aria-label=\"Infrared Spectroscopy\">\n  <button class=\"olsb-lightbox-close\" type=\"button\" aria-label=\"Close\">&times;<\/button>\n  <img decoding=\"async\" src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/2026\/03\/infrared-spectroscopy-greenhouse-effect-illustration.png\" alt=\"Infrared spectroscopy used to study molecular vibrations and greenhouse gases like carbon dioxide and methane\">\n<\/div>\n<script src=\"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-content\/uploads\/ols-blog\/infrared-spectroscopy-a-level-chemistry.js?v=d064ce4aca\" data-no-optimize=\"1\" data-cfasync=\"false\" data-pagespeed-no-defer nowprocket><\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>Analytical Chemistry Infrared Spectroscopy Infrared spectroscopy is one of the most powerful tools in modern chemistry, used to identify bonds, study molecular vibrations and even monitor greenhouse gases like CO\u2082 and methane. Discover how bond stretching, bending and dipole moments allow molecules to absorb infrared radiation and why this technique is essential for A-Level Chemistry. [&hellip;]<\/p>\n","protected":false},"author":12,"featured_media":1175,"parent":1145,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-17202","page","type-page","status-publish","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/17202","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/users\/12"}],"replies":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/comments?post=17202"}],"version-history":[{"count":0,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/17202\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/pages\/1145"}],"wp:attachment":[{"href":"https:\/\/www.onlinelearningsystem.net\/xyz\/wp-json\/wp\/v2\/media?parent=17202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}