Infrared band intensities and the complete quadratic force field for planar vibrations of gaseous benzene

Infrared absolute band intensities of the planar fundamental modes were measured for benzene and its deuterium homologs in the gas phase, and were successfully interpreted in terms of effective charges and charge flux parameters. The charge flux parameters were determined from the intensities by taking the effective charge on the hydrogen atom of benzene to be 0.125 e, a value which had previously been obtained from the nonplanar modes. The parameters determined were found to be quite consistent with those of other molecules. The complete quadratic planar force field of benzene was also introduced, the 273 assigned frequencies having been reproduced with a root-mean-square difference of 2.9 cm ^-1.