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Related Concept Videos

IR Spectroscopy: Molecular Vibration Overview01:24

IR Spectroscopy: Molecular Vibration Overview

3.5K
When Infrared (IR) radiation passes through a covalently bonded molecule, the bonds transition from lower to higher vibrational levels. The fundamental vibrational motions that result in infrared absorption can be classified as stretching or bending vibrations.
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
3.5K
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

1.3K
Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single...
1.3K
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration01:16

IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration

2.0K
A covalently bonded heteronuclear diatomic molecule can be modeled as two vibrating masses connected by a spring. The vibrational frequency of the bond can be expressed using an equation derived from Hooke's law, which describes how the force applied to stretch or compress a spring is proportional to the displacement of the spring. In this case, the atoms behave like masses, and the bond acts like a spring.
According to Hooke's law, the vibrational frequency is directly proportional to...
2.0K
Molecular Spectroscopy: Absorption and Emission01:14

Molecular Spectroscopy: Absorption and Emission

3.8K
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.
3.8K
UV–Vis Spectroscopy: Molecular Electronic Transitions01:16

UV–Vis Spectroscopy: Molecular Electronic Transitions

2.0K
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
2.0K
IR and UV–Vis Spectroscopy of Aldehydes and Ketones01:29

IR and UV–Vis Spectroscopy of Aldehydes and Ketones

6.7K
Infrared spectroscopy, also known as vibrational spectroscopy, is mainly used to determine the types of bonds and functional groups in molecules. In aldehydes and ketones, the carbonyl (C=O) bond shows an absorption around 1710 cm-1. The C=O bond vibration of an aldehyde occurs at lower frequencies than that of a ketone. In addition to the C=O absorption in an aldehyde, the aldehydic C–H bond also gives two peaks in the 2700–2800 cm-1 range. This absorption, coupled with the...
6.7K

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Related Experiment Video

Updated: Oct 25, 2025

Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
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Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid

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Molecular Vibrations Are Not Asymmetric.

James A de Haseth1

  • 1Infrared and Raman Courses, Inc., Athens, GA, USA.

Applied Spectroscopy
|August 6, 2021
PubMed
Summary

Confusing "asymmetric" and "antisymmetric" vibrations in spectroscopy is common. This study clarifies that only "antisymmetric" vibrations are correct, as "asymmetric" implies molecular rotation or translation.

Area of Science:

  • Molecular spectroscopy
  • Vibrational analysis
  • Quantum chemistry

Background:

  • Infrared (IR) and Raman spectroscopy are crucial for identifying molecular vibrations.
  • Misnaming vibrations as "asymmetric" is a frequent error in spectral analysis.
  • This nomenclature error can lead to misinterpretation of molecular structures and dynamics.

Purpose of the Study:

  • To address the common confusion between "asymmetric" and "antisymmetric" vibrational modes.
  • To provide a clear, symmetry-based explanation for the correct terminology in vibrational spectroscopy.
  • To enhance the accuracy of spectral data interpretation in IR and Raman studies.

Main Methods:

  • Analysis of molecular symmetry operations.
  • Application of group theory principles to vibrational modes.
Keywords:
Infrared spectra interpretationRaman spectra interpretationvibrational nomenclature

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  • Comparison of "asymmetric" and "antisymmetric" definitions in the context of molecular motion.

    • Main Results:

    • "Asymmetric" vibrations, if they existed, would involve molecular translation or rotation.
    • True vibrational modes are classified as symmetric or antisymmetric based on symmetry operations.
    • The term "antisymmetric" accurately describes vibrations that change sign upon specific symmetry operations.

    Conclusions:

    • The term "asymmetric vibration" is fundamentally incorrect in molecular spectroscopy.
    • "Antisymmetric vibration" is the precise and correct term, supported by molecular symmetry principles.
    • Correct terminology is essential for accurate interpretation of infrared and Raman spectra.