2ND-ORDER PERTURBATION-THEORY CORRECTIONS TO EFFECTIVE FERMI RESONANCE COUPLING-CONSTANTS

Second-order perturbation theory corrections to effective Fermi resona nce coupling constants have been derived analytically within the frame work of the traditional rectilinear normal coordinate approach to the analysis of anharmonic molecular vibrations. These corrections have be en evaluated for a range of methyl halide molecules (including deutera ted isotopomers) and are found to rationalise qualitatively discrepanc ies between the empirical effective Fermi resonance parameters and the oretical normal coordinate cubic force constants.