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Original scientific paper

Coupled Calculations of Vibrational Frequencies and Intensities, X. Calculation of Frequencies and Infrared and Raman Activities of Large Molecules

Bernhard Schrader ; Institut fur Physikalische und Theoretische Chemie, Universitat Essen, D-4300 Essen, FR Germany

Full text: english pdf 6.046 Kb


page 589-603

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The program package SPSIM can help organic chemists to
make better use of the information about the structure of large
molecules coded in vibrational spectra. The program is written in
FORTRAN 77. SPSIM cannot exactly reproduce experimental
spectra, it is rather a tool revealing the changes in the spectra
when the topology, geometry or bond distribution of a molecule
are changing; in addition to the frequencies for each vibration,
SPSIM calculates the 'activity measure' (AM) of each component
of the dipole moment vector and the polarizability tensor, the
relative AMs of the bands in the infrared and the Raman spectrum
together with AM based depolarization factors. AMs are zero for forbidden vibrations and, when they are Iarge, the respective
observed intensities are not usually small. The calculation
of AMs takes, even for large molecules only a few seconds of CPU time. As examples results are shown for stilbene, rotational
isomers of dinaphthylethylene and conformational isomers of a flexible peptide.


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