期刊
JOURNAL OF MOLECULAR SPECTROSCOPY
卷 269, 期 2, 页码 211-225出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jms.2011.07.005
关键词
G9 and G18 permutation-inversion groups; Internal rotation; Least squares fit program; Methyl acetate; Rotational transitions; Two inequivalent C3v tops
资金
- Land Nordrhein-Westfalen
- University of Bologna
- MIUR [356 KJX4SN_001]
- [ANR-08-BLAN-0054]
A program, called BELGI-Cs-2Tops, for fitting the high-resolution torsion-rotation spectra of molecules with two inequivalent methyl rotors and a plane of symmetry at equilibrium is described and applied to methyl acetate [CH3-O-C(=O)-CH3]. The G(18) permutation-inversion group-theoretical considerations (allowed coordinate transformations, symmetry species for the basis set functions and various operators, etc.) used in the design of the program are presented, followed by a description of the structure of the program, which uses an extreme principal axis method and a two-step diagonalization procedure. Restriction to molecules belonging to the C-s point group at equilibrium allows the use of real arithmetic throughout the program. This program was used to carry out a weighted least-squares fit of more than 800 new microwave and millimeter-wave measurements on ground-state transitions in methyl acetate, leading to root-mean-square deviations of 4 kHz for the microwave lines and of 40 kHz for the millimeter-wave lines, i.e., to residuals essentially equal to the experimental measurement errors, and to heights for two internal rotation barriers of 102 cm(-1) (acetyl CH3) and 422 cm(-1) (ester CH3). Some of the difficulties in determining molecular parameters for a two-top molecule from a data set containing only torsional ground state information are discussed. (C) 2011 Elsevier Inc. All rights reserved.
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