| Summary: | Previous assessment of the validity of an approximate force field has been based upon the accuracy with which it reproduced the observed frequencies. This is considered to be unsatisfactory. The present work compares the approximate force field with the harmonic general force field, which is regarded as the most precise description of intramolecular forces. As a preliminary to this, it has been necessary to review both, the methods available for force field calculation, and the different approximate force fields in current use, A consistent set of frequency data and molecular parameters have been compiled, and used to calculate general and approximate force, fields for thirty three molecules of types XY2 bent, XY3 pyramidal and XY4 tetrahedral, Finally, the comparison has revealed that two approximate force fields (Fadini's Stepwise Coupling and Nearest Solution Methods), provide a consistently good estimate of the harmonic general force field, and can therefore be recommended for general use.
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