Computational Simulation of Vibrational Overtone Spectral Regions: Sarin

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Authors
  1. Petryk, M.W.P.
Corporate Authors
Defence R&D Canada - Suffield, Ralston ALTA (CAN)
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, ~ω and ~ωχ, 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 di±cult 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 nonequiv

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Keywords
local mode;overtone transition;Fermi resonance;coupling;scaling factor;normal mode;ab initio;calculated frequencies;vibrational mode;molecular vibration;Chemical identification;Standoff detection
Report Number
DRDC-SUFFIELD-TR-2006-220 — Technical Report
Date of publication
01 Dec 2006
Number of Pages
51
DSTKIM No
CA029573
CANDIS No
527913
Format(s):
CD ROM

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