COMPUTING ROVIBRATIONAL LEVELS OF POLYATOMIC MOLECULES WITH CURVILINEAR INTERNAL VIBRATIONAL COORDINATES AND AN ECKART FRAME
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Date
2013
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Ohio State University
Abstract
We present a new procedure, 000000 (2013).} for computing a rovibrational spectrum of a polyatomic molecule. %and apply it to methane. The Schrodinger equation is solved, numerically exactly, by using a nested contracted basis. Rovibrational wavefunctions are computed in a $| v \rangle ert JKM \rangle $ basis, where $| v \rangle $ is a vibrational wavefunction and $ ert JKM \rangle $ is a symmetric top wavefunction. In turn, the $| v \rangle $ are obtained by solving a vibrational Schrodinger equation with basis functions that are products of contracted bend and stretch functions. At all stages of the calculation we exploit parity symmetry. The calculations are done in internal coordinates that facilitate the treatment of large amplitude motion. An Eckart molecule-fixed frame is used by numerically computing coefficients of the kinetic energy operator., 7449 (1991).} %new xgw The method is significantly more efficient than the previous method, 2937 (2004).} which uses a molecule-fixed frame attached to two vectors and vibrational basis functions that depend on $K$. % % The efficacy of the method is demonstrated by calculating a large number of converged $J=10$ methane rovibrational levels in the Tetradecad polyad (vibrational energies in the range 5100 - 6100 cm$^{-1}$). % using a global potential energy surface. No previous calculation of rovibrational levels of methane includes as many levels as we report in this paper.
Description
Author Institution: Chemistry Department, Queen's University, Kingston, Canada