Building a database of force constants based on scaled ab initio (SQM) results. I. Chlorobenzenes |
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| Institution: | 1. Department of Chemistry, Anhui University, Hefei 230601, China;2. School of Chemistry and Chemical Engineering, Yancheng Institute of Technology, Yancheng 224051, China;1. Cybernetica AS, Leirfossv. 27, 7038 Trondheim, Norway;2. Technology Centre Mongstad (TCM), Mongstad 71, 5954 Mongstad, Norway;3. Sintef AS, P.O. Box 4760 Torgarden, 7465 Trondheim, Norway;4. Norwegian University of Science and Technology (NTNU), N-7494 Trondheim, Norway;1. Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstraße 400, 01328 Dresden, Germany;2. Department of Chemistry, Radiochemistry, University of Helsinki, P.O. Box 55, 00014 University of Helsinki, Finland;3. Technische Universität Dresden, Chemie und Lebensmittelchemie, Mommsenstrasse 4, 01069 Dresden, Germany;4. Research Centre for Radwaste Disposal and Williamson Research Centre, School of Earth, Atmospheric and Environmental Science, University of Manchester, Manchester M13 9PL, UK |
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| Abstract: | As part of a project for developing a database of harmonic force constants for organic molecules, the complete force fields for chlorobenzene, ortho-, meta-, para-dichlorobenzene and sym-trichlorobenzene have been determined, on the basis of ab initio Hartree—Fock calculations combined with empirical adjustments. The latter serve to correct for systematic errors in the theory, and are applied at two stages: the geometry is corrected by using empirical offset forces during the optimization; force constants are corrected by a few scale factors according to the SQM (scaled quantum mechanical) force field procedure. With scale factors taken over fixed from benzene and only two new scale factors introduced for the chlorobenzenes, experimental frequencies are reproduced with mean deviations of about 10 cm?1. Some controversial assignments, still present in the deuterated derivatives, are discussed. Theoretical IR and Raman intensities have also been calcuated and used as semiquantitative information to assist assignments. |
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