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 Title: Numerically exact calculation of rovibrational levels of Cl−H2O Author(s): Wang, Xiao-Gang Contributor(s): Carrington, Tucker Subject(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)} Issue Date: 2014-06-19 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Wang, X.; Carrington, T. NUMERICALLY EXACT CALCULATION OF ROVIBRATIONAL LEVELS OF Cl−H2O. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.RC02 Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/50933 DOI: https://doi.org/10.15278/isms.2014.RC02 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-09-172015-04-14
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