Interpretation of the vibrational behavior of methyl and substituted methyl radicals perturbed by alkali halide molecules

The observed vibrational behavior of free and alkali halide-perturbed methyl radicals in low temperature inert matrices is rationalized on the basis of the relaxation of the molecular charge distribution of the methyl radical on vibration. It is shown that the primary interaction of an MX species with a methyl radical, is with the unoccupied, antibonding overlinea' ₁ orbital of the latter, which, via a perturbation treatment is linked to the electronic ground state out-of-plane bending force constant and quartic pottntial terms. The behavior of the halo substituted analogs is investigated in terms of the molecular orbital energy separation parameter, ∆ ∊, as a function of out-of-plane angle, and the number of available π-type ligand orbitals.