# THEORETICAL CALCULATION OF THE TORSIONAL SPECTRUM OF THE PARTIALLY DEUTERATED SPECIES OF METHANOL

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 Title: THEORETICAL CALCULATION OF THE TORSIONAL SPECTRUM OF THE PARTIALLY DEUTERATED SPECIES OF METHANOL Creators: Blasco, S.; Lauvergnat, D.; Coudert, L. H. Issue Date: 2003 Publisher: Ohio State University Abstract: The first spectroscopic investigations of the partially deuterated species of methanol, $CH_{2}DOH$ and $CD_{2}HOH$, have shown that these species display a dense torsional $spectrum^{a}$ difficult to assign. With a view toward understanding these spectra, a theoretical calculation of their rotation-torsion energy levels has been undertaken aided by ab initio calculations. This calculation accounts for the complicated torsion-rotation interaction displayed by these molecules and is based on the following features:\begin{itemize}\item The kinetic energy part of the Hamiltonian is calculated numerically taking into account all 12 internal degrees of freedom of the molecules. The angle of internal rotation is treated as an active $coordinate.^{b}$ \item The Schr\""{o}dinger equation for the internal rotation is solved using Gaussian $quadrature.^{c}$ \item Internal degrees of freedom corresponding to the other small amplitude motions are treated using the harmonic approximation, for each value of the internal angle of rotation corresponding to the DVR $grid.^{d}$ \item The potential energy function of the molecule is obtained using ab initio calculations. \end{itemize} After making some reasonable assumptions for the dipole moment function, the last step of the calculation involves evaluating the intensity of the rotation-torsion transitions. In the paper we hope to be able to show plots of room-temperature absorption spectra. Description: $^{a}$Mukhopadhyay, Perry, Butler, Herbst, and De Lucia, 57th International Symposium on Molecular Spectroscopy, paper RH06 (2002) and Mukhopad-hyay, Perry, Lock, and Klee, 57th International Symposium on Molecular Spectroscopy, paper RH07 (2002). $^{b}$Lauvergnat and Nauts, J. Chem. Phys. 116, 8560 (2002). $^{c}$Light and Ba\u{c}i\'{c},J. Chem. Phys. 87, 408 (1987). $^{d}$Lauvergnat, Nauts, Justum and Chauisat, J. Chem. Phys. 114, 6592 (2001). Author Institution: Laboratoire de Chimie Physique, Unit\'{e} mixte du C.N.R.S. et de I'Universit\'{e} Paris-Sud,-B\^{a}t; Laboratoire de Photophysique Mol\'{e}cuiaire, C.N.R.S., B\^{a}t. 350, Universit\'{e} Paris-Sud URI: http://hdl.handle.net/1811/20925 Other Identifiers: 2003-RH-07