Infrared-Active Vibrational Modes in Water

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This Demonstration shows the fundamental vibrations of the water molecule: symmetric stretch, asymmetric stretch and bending. Any vibration of the molecule is a combination of these normal modes. Also, in liquid water, rotations may cause an infrared absorption with motions restricted by hydrogen bonds. As a consequence of these librations, a broad absorption band occurs at lower wavelengths [1].

Contributed by: D. Meliga and S. Z. Lavagnino (January 2020)
Open content licensed under CC BY-NC-SA


Snapshot 1: water infrared spectrum; each peak is related to one of the three normal modes [2]

Snapshot 2: symmetric stretch: this vibration is infrared active as the dipole changes

Snapshot 3: overview of the three modes of vibration


[1] M. Chaplin. "Water Absorption Spectrum." (Nov 20, 2019)

[2] "Water IR Spectrum," NIST Chemistry WebBook, SRD 69. (Nov 20, 2019)


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