# AB INITIO DETERMINATION OF MOLECULAR PARAMETERS FOR ETHANE-LIKE MOLECULES

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 Title: AB INITIO DETERMINATION OF MOLECULAR PARAMETERS FOR ETHANE-LIKE MOLECULES Creators: Cooper, J. R.; Xu, Li-Hong; Moazzen-Ahmadi, N. Issue Date: 2004 Publisher: Ohio State University Abstract: A new method has been developed for the ab initio determination of several vibration-torsion-rotational spectroscopic parameters for a symmetric top molecule with an internal rotor. In contrast to existing $methodologies^{a,b}$ which employ vibrational contact transformations either numerically or algebraically, the present model treats the molecule as vibrationally static but with a density distribution characteristic of the vibrational wavefunction. The second-order rotational constants A and B and torsional constant F, distortion parameters $D_{J}, D_{K}$, and $D_{JK}$, and torsional distortion parameters $D_{m}, D_{Jm}$, and $D_{Km}$ have been determined for a series of ethane-like molecules from the results of ab initio calculations done at the CCSD(T) level. The technique has been applied to the molecules $CH_{3}CH_{3}, CH_{3}CD_{3}, CD_{3}CD_{3}$, and $CH_{3}SiH_{3}$ with very promising results. Preliminary results for the potential constants $F_{3J}$ and $F_{3K}$ are also in excellent agreement with global fit values. Description: $^{a}$Y.-B. Duan, L. Wang, X.T. Wu, I. Mukhopadhyay, and K. Takagi, J. Chem. Phys. 111, 2385 (1999). $^{b}$T.J. Lukka and E. Kauppi, J. Chem. Phys. 103, 6586 (1995). Author Institution: Department of Physics and Astronomy, University of Calgary; Department of Physical Sciences, University of New Brunswick; Department of Physics and Astronomy, University of Calgary URI: http://hdl.handle.net/1811/21358 Other Identifiers: 2004-RJ-10