Name: molecular energy levels in spectroscopy
Uploaded: 2024-12-05T18:32:03.000Z
Duration: 1 min 14 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Earth and Space Science

Space Systems

3.3.9-12.B

molecular-spectroscopy-absorption-and-emission

Molecular Spectroscopy: Absorption and Emission

In a molecule, discrete energy states called quantum states exist. Each quantum state&#8212;be it electronic, vibrational, or rotational&#8212;is unique, with a definite energy value, and separated from others of its type by energy gaps.
On absorbing a photon of electromagnetic radiation, a molecule can be excited to a higher energy level. As a result, it undergoes relaxation to a lower energy level by emitting a photon.
The molecule can only absorb or emit photons of specific energies that match the energy gaps between these energy levels. So, each transition is frequency- or wavelength-dependent.
Accordingly, different kinds of excitation occur in a molecule, depending on the radiation wavelength.
For example, photons in the microwave region are absorbed to alter internal bond rotation, while those in the infrared region possess the energy required to change the frequency of bond vibrations.
Photons in the UV&#8211;visible range can excite electrons to higher electronic energy states.

molecular spectroscopy: absorption and emission

Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational and vibrational energy levels. Each energy level is separated by an energy gap, with the gaps between adjacent electronic, vibrational, and rotational levels varying significantly. The three types of energy levels in a diatomic molecule are shown in Figure 1.
<img alt="Potential energy surface diagram: vibrational, rotational levels; excited, ground states, molecular spectroscopy." src="/files/ftp_upload/13024/13024_PT_Figure_1.svg" style="text-align: center; height: 400px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
Figure 1: The three types of energy levels in a diatomic molecule.
A molecule can absorb energy in the form of a photon from electromagnetic radiation and use that energy to excite the molecule into a higher energy state. During this process, changes can occur in the rotation around a bond, the frequency of bond vibration, or the transition of an electron from its ground state (the lowest energy state) to an excited state (a higher energy level). When the excited-state molecule returns to its ground state, it emits radiation. The energy of the absorbed or emitted photon is equivalent to the energy gap between the two energy levels involved in the transition. Therefore, each transition is dependent on the wavelength or frequency of the radiation.
Due to the varying magnitudes of energy gaps, the wavelengths of radiation absorbed during these transitions differ. For example, the energy consumed or released during the transition of a specific rotation in a molecule is in the range of microwave radiation. In contrast, the energy of infrared radiation corresponds to changes in bond vibrations. Furthermore, photons in the UV&#8211;visible range can excite an electron to a different orbital, particularly in the case of molecules with conjugated double bonds.

Molecules possess discrete energy levels called quantum states. Unlike atoms, which have simpler energy levels, molecules possess additional rotational ...

Education

JoVE Core

Analytical Chemistry

Unit 1

Introduction to Molecular Spectroscopy

KEY TERMS AND CONCEPTS

molecular energy levels in spectroscopy

Molecular spectroscopy describes how molecules absorb and emit light by moving between energy levels. These levels are called quantum states. Unlike atoms, molecules also have rotational and vibrational energy levels, so their energy structure is more complex.

Each level is separated by an energy gap. The gaps between electronic, vibrational, and rotational levels are very different in size. A diatomic molecule can be used to show these three kinds of energy levels.

A molecule can absorb a photon from electromagnetic radiation and use that energy to move to a higher state. That change may involve rotation around a bond, a change in bond vibration, or an electron moving from the ground state to an excited state. When the molecule falls back to the ground state, it emits radiation.

The energy of the absorbed or emitted photon matches the energy gap between the two levels involved. Because the gaps are different, the wavelength or frequency of the radiation also changes with the transition. Rotational changes usually involve microwave radiation. Bond vibrations match infrared radiation. In molecules with conjugated double bonds, UV-visible photons can raise an electron to a different orbital.

Molecular Energy Levels in Spectroscopy

dual nature of electromagnetic (em) radiation

dual-nature-of-electromagnetic-em-radiation

EM Spectrum, Waves, and Photon Energy

Electromagnetic radiation has both wave and particle features. It includes electric and magnetic field components that oscillate in planes perpendicular to each other. These fields are also perpendicular to the direction the radiation moves through space. As a wave, electromagnetic radiation is described by wavelength and frequency. Wavelength is the distance between two consecutive peaks or troughs. Frequency is the number of wave cycles that pass a point in a fixed time. The electromagnetic...

interaction of em radiation with matter: spectroscopy

interaction-of-em-radiation-with-matter-spectroscopy

EM Radiation and Matter in Spectroscopy

Electromagnetic radiation and matter interact in ways that reveal details about atoms and molecules. In spectroscopy, scientists study how EM radiation is absorbed, emitted, transmitted, reflected, or scattered by a substance. This helps identify its chemical composition and properties. EM radiation behaves as both a wave and a particle. As a wave, it has intensity and amplitude. Intensity, also called irradiance, is the number of photons that strike a given area in a certain time. Amplitude...

Molecular spectroscopy describes how molecules absorb and emit light by moving between energy levels. These levels are called quantum states. Unlike atoms, molecules also have rotational and vibrational energy levels, so their energy structure is more complex. Each level is separated by an energy gap. The gaps between electronic, vibrational, and rotational levels are very different in size. A diatomic molecule can be used to show these three kinds of energy levels. A molecule can absorb a...

spectrophotometry: introduction

Spectrophotometry for Absorption Spectra

Spectrophotometry measures how a material absorbs, reflects, diffracts, or transmits electromagnetic radiation. It compares the intensity of radiation before and after it interacts with the material. The result shows how the material responds to different wavelengths. A spectrophotometer is the device used for this measurement. It includes a source of electromagnetic radiation, a slot for the sample, and a detector. The detector measures the radiation that leaves the material, including...

ultraviolet and visible (uv&ndash;vis) spectroscopy: overview

ultraviolet-and-visible-uvvis-spectroscopy-overview

UV-Vis Spectroscopy for Light Absorption

UV-Vis spectroscopy measures how materials absorb ultraviolet and visible light. It is a useful analytical method because it is versatile, simple to use, and gives results quickly. Scientists use it for both qualitative and quantitative analysis. When UV-Vis radiation passes through a sample, molecules absorb specific wavelengths based on the energy needed for electronic transitions. This absorption moves atoms or molecules from a ground state to an excited state. If a molecule absorbs UV...

uv&ndash;vis spectroscopy: molecular electronic transitions

uvvis-spectroscopy-molecular-electronic-transitions

UV-Vis Spectroscopy and Molecular Absorption

UV-Vis spectroscopy shows how molecules absorb ultraviolet and visible light. It is used to study electronic structure by tracking how electrons move between molecular orbitals. The absorbed light must match the energy gap between the ground state and an excited state. In this process, an electron moves from the highest occupied molecular orbital, or HOMO, to the lowest unoccupied molecular orbital, or LUMO. This jump raises the electron to a higher energy level. The energy difference between...

uv&ndash;vis spectrometers

UV-Vis Spectrophotometer Parts and Samples

A UV-visible spectrophotometer measures how much UV and visible light a sample absorbs. It uses a light source, a wavelength selector, a sample holder, and a detector to build the spectrum. This makes it useful for checking liquid samples in the lab. The light source depends on the region being measured. A deuterium lamp provides UV radiation, and a tungsten lamp provides visible radiation. A monochromator or prism acts as a diffraction grating and splits the incoming light into different...

uv&ndash;vis spectrum

How Molecular Structure Shapes UV-Vis Bands

UV-Vis spectroscopy shows how a molecule absorbs light in the ultraviolet and visible ranges. When light passes through a substance, some of it is absorbed and the rest is reflected or transmitted. Molecules that absorb between 180 and 400 nm give a UV spectrum, while absorption in the 400 to 780 nm range gives a visible spectrum. A UV-Vis spectrum is a plot of absorbance versus wavelength. The y-axis shows molar absorptivity, ε, or log ε, and the x-axis shows wavelength. Absorbance describes...

uv&ndash;vis spectroscopy: beer&ndash;lambert law

Using Absorbance to Find Concentration

The Beer-Lambert law links absorbance, concentration, and path length in a solution. It is based on ideas from Johann Heinrich Lambert and August Beer. Their work helps explain how light changes as it passes through a medium. Lambert's law says that when light passes through a medium, the loss in intensity is directly proportional to the original intensity and the path length. Beer’s law adds that the transmittance of a solution stays constant if the product of concentration and path length...

photoluminescence: fluorescence and phosphorescence

photoluminescence-fluorescence-and-phosphorescence

Light Emission from Excited Molecules

Photoluminescence is light emission from molecules after they absorb light energy. A substance takes in photons, which raises electrons to excited energy levels. The electrons then relax back to the ground state and release light. This process appears in many materials, including semiconductors, organic compounds, and inorganic compounds. The main role of electron spin helps separate photoluminescence into fluorescence and phosphorescence. In a singlet spin state, two electrons share the same...

variables affecting phosphorescence and fluorescence

variables-affecting-phosphorescence-and-fluorescence

Factors That Change Light Emission in Molecules

Fluorescence and phosphorescence depend on several factors that change how molecules emit light. These effects matter in analytical chemistry, biological imaging, and materials science because they help scientists detect molecular properties and see cellular structures. Molecular structure is one of the main influences. Aromatic compounds with low-energy pi-bonding to pi-non-bonding transitions often give strong fluorescence. Aliphatic and alicyclic carbonyl compounds, as well as highly...

deactivation processes: jablonski diagram

Jablonski Diagram: Light Loss Pathways

Jablonski diagrams show how excited molecules lose energy after absorbing light. They are used to track both light-emitting and non-light-emitting steps in luminescence. The diagram gives a simple picture of the energy states a molecule can move through. The lowest line in a Jablonski diagram is the ground-state energy of the molecule. This state is usually a singlet state, and it represents the condition of most molecules in solution at room temperature. The lines above it show vibrational...

photoluminescence: applications

Fluorescent and Phosphorescent Analysis

Photoluminescence is useful in chemical analysis because it is sensitive and selective. It can support both direct and indirect measurements of an analyte, which is the substance being tested. When an analyte has a strong quantum yield, it can be measured directly by fluorescence or phosphorescence. Indirect analysis is used when the analyte is not naturally fluorescent or phosphorescent, or when its quantum yield is poor. One approach is to react the analyte with a reagent to make a...

fluorescence and phosphorescence: instrumentation

fluorescence-and-phosphorescence-instrumentation

Measuring Fluorescence and Phosphorescence

Fluorometers and spectrofluorometers are instruments used to measure molecular fluorescence. They do this by choosing specific excitation and emission wavelengths. The two instruments use different light sources and wavelength-selection methods. A fluorometer uses absorption interference filters to select the excitation and emission wavelengths. Its excitation source is usually a low-pressure mercury vapor lamp. This lamp gives intense lines across the ultraviolet and visible regions.

key terms and concepts

Explore how molecules absorb and emit light through rotational, vibrational, and electronic energy levels, with examples from microwave, infrared, and UV-visible radiation.

Molecular Energy Levels in Spectroscopy | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Physical Science

Waves and Electromagnetic Radiation

3.2.9-12.X

Louisiana Student Standards for Science

High School

Earth Science

Earth’s Place In The Universe

HS-ESS1-2

Chemistry

motion-and-stability-forces-and-interactions

Motion And Stability: Forces And Interactions

HS-PS2-6

Minnesota Academic Standards in Science

1.1.1 9L.4.2.1.1

Arizona Science Standards

HS+C.P1

HS+C.P1U1.2

Texas Essential Knowledge and Skills

Physics

PHYS.8

PHYS.8.F

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

Matter and Its Interactions

C-PS1-4

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

C-PS4-4

C-PS4-5

the-principle-of-superposition-and-the-gravitational-field

The Principle of Superposition and the Gravitational Field

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Escape Velocity

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Circular Orbits and Critical Velocity for Satellites

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Kepler's Third Law of Planetary Motion

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Nuclear Fusion

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Nuclear Power

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Nuclear Fission

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Nuclear Transmutation

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Atomic Structure

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Radioactivity and Nuclear Equations

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Nuclear Stability

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Students who demonstrate understanding can develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun's core to release energy in the form of radiation.  Clarification Statement: Emphasis is on the energy transfer mechanisms that allow energy from nuclear fusion in the sun's core to reach Earth.  Examples of evidence for the model include observations of the masses and lifetimes of other stars, as well as the ways that the sun's radiation varies due to sudden solar flares ("space weather"), the 11-year sunspot cycle, and non-cyclic variations over centuries.  Assessment Boundary: Assessment does not include details of the atomic and sub-atomic processes involved with the sun's nuclear fusion.

3.3.9-12.A

Emission Spectra

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atomic-spectroscopy-absorption-emission-and-fluorescence

Atomic Spectroscopy: Absorption, Emission, and Fluorescence

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Detection of Black Holes

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Space-Time Curvature and the General Theory of Relativity

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The Wave Nature of Light

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Nuclear Binding Energy

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Metal Flame Emission

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Atomic Emission Spectroscopy: Instrumentation

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Atomic Absorption Spectroscopy: Radiation and Light Sources

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Students who demonstrate understanding can construct an explanation of the Big Bang theory based on astronomical evidence of light spectra, motion of distant galaxies, and composition of matter in the universe.  Clarification Statement: Emphasis is on the astronomical evidence of the red shift of light from galaxies as an indication that the universe is currently expanding, the cosmic microwave background as the remnant radiation from the Big Bang, and the observed composition of ordinary matter of the universe, primarily found in stars and interstellar gases (from the spectra of electromagnetic radiation from stars), which matches that predicted by the Big Bang theory (3/4 hydrogen and 1/4 helium).  Assessment Boundary:

Spectrophotometry: Introduction

Spectrophotometry is the quantitative measurement of the absorption, reflection, diffraction, or transmission of electromagnetic radiation through a ...

Atomic Emission Spectroscopy: Overview

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Ultraviolet and Visible (UV&ndash;Vis) Spectroscopy: Overview

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Atomic Emission Spectroscopy: Lab

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Flame Photometry: Overview

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The Greek philosopher Democritus proposed that everything on Earth is made up of tiny particles called atomos, Greek for &#34;indivisible,&#34; from which ...

Students who demonstrate understanding can communicate scientific ideas about the way stars, over their life cycle, produce elements.  Clarification Statement: Emphasis is on the way nucleosynthesis, and therefore the different elements created, varies as a function of the mass of a star and the stage of its lifetime.  Assessment Boundary: Details of the many different nucleosynthesis pathways for stars of differing masses are not assessed.

3.3.9-12.C

Tidal Forces

The origin of Earth&#39;s ocean tides has been a subject of continuous investigation for over 2000 years. However, the work of Newton is considered to be ...

Students who demonstrate understanding can use mathematical or computational representations to predict the motion of orbiting objects in the solar system.  Clarification Statement: Emphasis is on Newtonian gravitational laws governing orbital motions, which apply to human-made satellites as well as planets and moons.  Assessment Boundary: Mathematical representations for the gravitational attraction of bodies and Kepler's Laws of orbital motions should not deal with more than two bodies, nor involve calculus.

3.3.9-12.D

Molecular Energy Levels in Spectroscopy

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