The force field, vibration frequencies, normal co-ordinates, infra-red and Raman intensities for benzene

Abstract

A quadratic force field with twenty-six non-zero constants is chosen for benzene and reasons are given for preferring the constants chosen when alternative values are possible. Using this field all the vibration frequencies of C6H6, C6H5D , ortho-, meta- and para-C6H4D2, sym.- and vic.-C6H3D3, para-C6H2D4 and C6D6 are calculated and found to agree with the experimental values of Ingold and coworkers to better than 2 %. Four dipole moment derivative parameters are introduced to give satisfactory indications of the infra-red absorption intensities and ten polarizability parameters are used to give satisfactory indications of Raman shift intensities and degrees of polarization. The alternative B2u class assignment of Mair & Hornig is also discussed.