Reinvestigation of the ν3–ν6 Coriolis interaction in trifluoroiodomethane

Abstract

The lowest-frequency fundamental ν₆ of trifluoroiodomethane (CF₃I) has never been directly observed and analyzed at high resolution in the gas phase. The ν₆(e) level interacts with ν₃(a₁) at 286.297 cm⁻¹via a b-axis Coriolis interaction, which perturbs the rotational structure of both levels. In this work, we report low-J microwave transitions (for J ranging from 0–2) within the ν₆ vibrational level. The l-type doubling observed in our spectrum agreed poorly with the predictions of previously published models of the interacting ν₃–ν₆ levels, prompting us to refine the model. We performed ab initio anharmonic force-field calculations, which were used to constrain some of the parameters, and which served as a check on some of the floated parameters. We fit a dataset consisting of 3593 transitions, which combined our measurements with previous microwave, millimeter wave, and high-resolution infrared observations. A reasonable set of fit parameters is obtained with ν₆ = 267.28 cm⁻¹, but we cannot rule out a lower value of ν₆ = 261.5 cm⁻¹ consistent with analyses of the vibrational level structure.