PSEUDO-$r_{e}$ STRUCTURES FROM EXPERIMENTAL ROTATIONAL CONSTANTS AND AB INITIO VIBRATION-ROTATION CONSTANTS

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2000

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Ohio State University

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The determination of accurate molecular structures from spectroscopic data has been remains a formidable challenge. Inspired by the close agreement of experimental and theoretical centrifugal distortion constants and inertial $defects^{a}$, we explored the possibility of using vibration-rotation constants from ab initio calculations together with experimental ground state constants to derive approximate $r_{e}$ structures. In the past, this has been done successfully for (very) small molecules with large basis sets at high levels of calculation (for an example, $see^{b}$), we were interested in finding you whether MP2 calculations with small basis sets yield sufficiently accurate vibration-rotation constants for larger molecules. This method was tested with MP2/6-31G(d) calculations for the $COCl_{2}. HCOCl$, $FCOCl$, and $HCOOH$, for which near equilibrium structures derived from experimental data are available in the literature. It was subsequently used to reevaluate the structures of $CF_{2}NH$, $CF_{e}NCl$, $CH_{3}OCOCl$, $CH_{3}OCOCN$, and two conformers of $CH_{3} CH_{2} PH_{2}$. Many, but not all, problems encountered in deriving meaningful structures are significantly reduced. It appears that the structures are comparable to $r^{\rho}_{m} c$ and $r^{(1)}_{m}/r^{(2)}_{m} d$ structures.

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$^{a}$P. Groner. J. R. Durig. D. D. DesMarteau, and S.-H. Hwang, J. Chem. Phys. 110, 9411(1999), P. Groner. J. R. Durig, and D. D. DesMarteau, J. Chem. Phys. 105.7263(1996). $^{b}$M. Oswald, J. Fl\""{u}gge, and P. Botschwina, J. Mol. Struct. 320, 227(1994). $^{c}$M. D. Harmony, in: J. R. During(Ed.), Vibrational Spectra and Structure, (Elsevier. Amsterdam. 2000) vol.24. $^{d}$J.K.G. Watson, A. Roytburge, and W. Ulrich, J. Mol. Spectrosc. 196, 102(199).
Author Institution: Department of Chemistry, University of Missouri - Kansas City

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