Combined analysis of microwave and infrared spectra of methyl iodide: rotational and l-type doubling constants of the v5, v3+ v6 and v2 states

Abstract

The rotational constant B and the l-type doubling constant q were determined for the v 5, v 3+ v 6 and v 2, states of CH 2I from the microwave transition frequencies, in combination with the infrared data previously reported. Since these vibrational states were coupled through the Fermi resonance and the xy-type E-E and A 1-E Coriolis resonances, the analysis was made by setting up and solving the complete form of the secular determinants of the energy matrices. The rotational and l-type doubling constants were determined as B 5, = 0.250 173 cm −1, B 36 = 0.247 600 cm −1, B 2 = 0.249 369 cm −1, q 5 = −0.000 027 cm −1 and q 36 = −0.000 179 cm −1, which are unperturbed by Fermi and Coriolis interactions. Other band constants for v 5 and v 3+ v 6 were also refined in accordance with the new values of B 5 and B 36. The present study indicated that the combined analysis of microwave and infrared spectral data was useful for the precise determination of vibration-rotation, levels in the perturbed system.