Ab Initio Prediction of Vibration-Rotation Spectra: HCCF, HFCO, SiH3+ and CH2
Loading...
Date
1990
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Knowledge of a force field expanded through quartic displcements. together with a dipole field expanded through cubic displacements, yields all the harrnonic and unharmonic molecular properties of interest to infrared spectroscopists. Such force fields may also explain much of the mechanism behind IVR. The ab initio quantum chemist can now calculate these fields, either at the SCF level or with the inclusion of elecuon correlation effects. For accurate predictions, it is important to include electron correlation effects for at least the quadratic part of the force fields. Here we report three studies using the MP2 method with large basis acts for the full quartic fields: HCCF, for which a large quantity of experimental data has been recently analysed by Holland. Newnham and Mills. The MP2 calculations are so accurate that errors in the experimental assignmental became apparent HFCO. where the theoretical anharmonic constats are helpful in interpreting the highly excited vibrational stases probed by Moore and coworkers. SiH3+. whose high resolution absorption spectra has recently been detected in the Davies group. This straightforward way of calculating spectroscopic properties is an extremely valuable tool for the understanding of spectroscopy. More exact calculations have been performed on singlet methylcne. in an attempt to understand the very complex visible spectra. The potential energy surfaces of the two electronic states, which interact by the Renner-Teller effect. are calculate using the interrnally-contracted multi-reference configuration interaction technique. The full rotation-vibration Harniltonian is solved variationally, including Renner-Teller coupling clements calculated ab initio. This calculation demonstrates the state of the art in the ab initio prediction of rovibronic spectra of triatomic molecules, and improves our understanding of the experimental data.
Description
Author Institution: University Chemical Laboratory