The Non-Planar Vibrations of Benzene

A thorough normal coordinate treatment has been carried out for the non-planar vibrations of benzene and its deuterium derivatives. The analysis has led to a critical survey of the assignments, and has furnished strong independent support for those advanced by Pitzer and Scott. It has also furnished values for all eight force constants of the complete harmonic potential function. For four of the constants two sets of values were obtained, both of which are physically reasonable and which reproduce the frequencies equally well. It was not possible to decide between them. The force constants were then used to calculate frequencies for the various deuterobenzenes. Nearly sixty such frequencies were evaluated, of which about forty could be checked against experiment. With four exceptions the errors are less than 1.5 percent. Lastly, certain valence-force constants pertaining to hydrogen vibrations have been determined.