THE FORCE FIELD, VIBRATION FREQUENCIES, NORMAL CO-ORDINATES, INFRA-RED AND RAMAN INTENSITIES

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 CH6, C6H5D, ortho-, metaandpara-C6H4D2, sym.and vic.-C6H3D3,paraC6H2D4 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.