PSEUDO-$r_{e}$ STRUCTURES FROM EXPERIMENTAL ROTATIONAL CONSTANTS AND AB INITIO VIBRATION-ROTATION CONSTANTS
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Date
2000
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Publisher
Ohio State University
Abstract
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.
Description
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Author Institution: Department of Chemistry, University of Missouri - Kansas City
Author Institution: Department of Chemistry, University of Missouri - Kansas City