Numerically exact calculation of rovibrational levels of Cl−H2O

Wang, Xiao-Gang

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https://hdl.handle.net/2142/50933 Copy

Description

Title

Numerically exact calculation of rovibrational levels of Cl−H2O

Author(s)

Wang, Xiao-Gang

Contributor(s)

Carrington, Tucker

Issue Date

2014-06-19

Keyword(s)

Theory and Computation

Abstract

Large amplitude vibrations of Van der Waals clusters are important because they reveal large regions of a potential energy surface (PES). To calculate spectra of Van der Waals clusters it is common to use an adiabatic approximation. When coupling between intra- and inter-molecular coordinates is important non-adiabatic coupling cannot be neglected and it is therefore critical to develop and test theoretical methods that couple both types of coordinates. We have developed new product basis and contracted basis Lanczos methods for Van der Waals complexes and tested them by computing rovibrational energy levels of Cl$^-$H$_2$O. The new product basis is made of functions of the inter-monomer distance, Wigner functions that depend on Euler angles specifying the orientation of H$_2$O with respect to a frame attached to the inter-monomer Jacobi vector, basis functions for H$_2$O vibration, and Wigner functions that depend on Euler angles specifying the orientation of the inter-monomer Jacobi vector with respect to a space-fixed frame. %tc why not include the angles of the Jacobi vector? An advantage of this product basis is that it can be used to make an efficient contracted basis by replacing the vibrational basis functions for the monomer with monomer vibrational wavefunctions. Due to weak coupling between intra- and inter-molecular coordinates, only a few tens of monomer vibrational wavefunctions are necessary. The validity of the two new methods is established by comparing energy levels with benchmark rovibrational levels obtained with polyspherical coordinates and spherical harmonic type basis functions. %tc i add For all bases, product structure is exploited to calculate eigenvalues with the Lanczos algorithm. % % For Cl$^-$H$_2$O, we are able, for the first time, to compute accurate splittings due to tunnelling between the two equivalent $C_s$ minima. We use the PES of Rheinecker and Bowman (RB).\footnote{ J. Rheinecker and J. M. Bowman, \newblock J. Chem. Phys. {\bf 124} 131102 (2006); J. Rheinecker and J. M. Bowman, \newblock J. Chem. Phys. {\bf 125} 133206 (2006)} Our results are in good agreement with experiment for the five fundamental bands observed.\footnote{S. Horvath, A. B. McCoy, B. M. Elliott, G. H. Weddle, J. R. Roscioli, and M. A. Johnson \newblock J. Phys. Chem. A {\bf 114} 1556 (2010)}

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/50933

DOI

https://doi.org/10.15278/isms.2014.RC02

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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