Computational Simulation of Vibrational Overtone Spectral Regions: Sarin
Abstract
In sarin (isopropyl methylphosphonofluoridate) there are ten nonequivalent CH oscillators. Ab initio calculations at the HF / 6-311++G(2d,2p) level have been used to determine the vapour phase local mode parameters, w and wx, for each oscillator in the two spectrally significant conformers of sarin, as well as inter-oscillator coupling parameters. These above parameters, in conjunction with dipole moment functions derived from ab initio calculations, were used to perform harmonically coupled anharmonic oscillator (HCAO) calculations, thereby enabling the simulation of vibrational overtone spectral regions in a room-temperature sample of sarin. It was determined that the computationally-intensive HCAO approach is necessary to predict the lower vibrational overtone regions (i. e., first to third overtones) as a simpler "non-HCAO" approach (which does not allow pairwise harmonic coupling among adjacent oscillators) failed to accurately reproduce the HCAO-simulated spectral regions. The present work, which was carried out without recourse to the experimental sarin spectral regions, illustrates that it is currently feasible to predict the absorption spectra of species which are difficult to synthesize, handle, or otherwise acquire. In addition to their utility in guiding experimental investigations, the simulated overtone spectral regions will be necessary to correctly assign experimental overtone spectra owing to the large number of similar but nonequivalent CH oscillators present in sarin.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2006
- Accession Number
- ADA472801
Entities
People
- M. W. Petryk