The role of electrical anharmonicity in determining intensity in the 2100 cm-1 region of the water spectrum

McCoy, Anne B

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https://hdl.handle.net/2142/59133 Copy

Description

Title

The role of electrical anharmonicity in determining intensity in the 2100 cm-1 region of the water spectrum

Author(s)

McCoy, Anne B

Issue Date

2014-06-18

Keyword(s)

Comparing theory and experiment

Abstract

The origins of the intensity of the feature in the spectrum of liquid water near 2100 \wn\ are investigated through calculations of the spectra of water clusters. The spectra of thirteen water clusters with six or fewer water molecules are calculated using low-order expansions of the potential and dipole surfaces in internal and normal mode coordinates. The results are dissected to interpret the origins of the intensity in 2100 \wn\ region of the spectra. It is found that the intensity near 2100 \wn\ can be attributed to combination bands involving the HOH bend and intermolecular vibrations that break the hydrogen bonding network. Based on the robustness of a feature near 2100 \wn\ in all of the water clusters studied, it is inferred that a similar assignment can be made for the spectrum of liquid water. When the origins of the intensity near 2100 \wn\ is analyzed from calculations that used internal coordinates to expand the potential and dipole surfaces, the leading contribution to the intensity is attributed to large second derivatives of the dipole moment with respect to the internal coordinates that are excited, or electrical anharmonicity. This picture changes if the derivatives of the potential and dipole surfaces are taken with respect to normal modes. In this representation, the second derivatives of the dipole moment are often vanishingly small, while the mixed third and fourth derivatives of the potential become quite large. Based on this result, mechanical anharmonicity appears to be responsible for the intensity in the 2100 \wn\ region. This strong dependence of the interpretation of the origins of the intensity in the 2100 \wn\ region of the water spectrum is also investigated and discussed.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

en

Permalink

http://hdl.handle.net/2142/59133

DOI

https://doi.org/10.15278/isms.2014.WI11

Copyright and License Information

Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/

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