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Ab Initio Potential Energy Surfaces and the Calculation of Accurate Vibrational FrequenciesDue to advances in quantum mechanical methods over the last few years, it is now possible to determine ab initio potential energy surfaces in which fundamental vibrational frequencies are accurate to within plus or minus 8 cm(exp -1) on average, and molecular bond distances are accurate to within plus or minus 0.001-0.003 Angstroms, depending on the nature of the bond. That is, the potential energy surfaces have not been scaled or empirically adjusted in any way, showing that theoretical methods have progressed to the point of being useful in analyzing spectra that are not from a tightly controlled laboratory environment, such as vibrational spectra from the interstellar medium. Some recent examples demonstrating this accuracy will be presented and discussed. These include the HNO, CH4, C2H4, and ClCN molecules. The HNO molecule is interesting due to the very large H-N anharmonicity, while ClCN has a very large Fermi resonance. The ab initio studies for the CH4 and C2H4 molecules present the first accurate full quartic force fields of any kind (i.e., whether theoretical or empirical) for a five-atom and six-atom system, respectively.
Document ID
20020034941
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Lee, Timothy J.
(NASA Ames Research Center Moffett Field, CA United States)
Dateo, Christopher E.
(NASA Ames Research Center Moffett Field, CA United States)
Martin, Jan M. L.
(Limburgs Universitair Centrum Belgium)
Taylor, Peter R.
(San Diego Supercomputer Center San Diego, CA United States)
Langhoff, Stephen R.
Date Acquired
August 20, 2013
Publication Date
January 1, 1995
Subject Category
Physics Of Elementary Particles And Fields
Meeting Information
Meeting: 50th Symposium on Molecular Spectroscopy
Location: OH
Country: United States
Start Date: June 12, 1995
End Date: June 16, 1995
Funding Number(s)
PROJECT: RTOP 232-01-04
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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