Microwave spectra of methyl iodide in the excited vibrational states. The Fermi resonance between the ν5 and ν3 + ν6 states

Abstract

Microwave spectra of CH 3I for the transitions J = 1 ← 0 in various excited vibrational states have been measured and the vibration-rotation interaction constants, α B , and the nuclear quadrupole coupling constants, eQq, of the iodine nucleus have been determined. Sum rule has been confirmed for the observed values of α B , except that for the ν 3 + ν 6 state. This anomaly indicates that the ν 3 + ν 6 state is strongly perturbed by the Fermi resonance with the ν 5 state. The degree of mixing has been found to be b 2 = 0.134, which leads to k 356 = 34 ± 2 cm −1, in a fairly good agreement with the value obtained by the analysis of the infrared spectra.