Reinvestigation of the - Coriolis interaction in trifluoroiodomethane.

The lowest-frequency fundamental of trifluoroiodomethane (CFI) has never been directly observed and analyzed at high resolution in the gas phase. The (e) level interacts with (a) at 286.297 cm a -axis Coriolis interaction, which perturbs the rotational structure of both levels. In this work, we report low- microwave transitions (for ranging from 0-2) within the vibrational level. The -type doubling observed in our spectrum agreed poorly with the predictions of previously published models of the interacting - levels, prompting us to refine the model. We performed 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 = 267.28 cm, but we cannot rule out a lower value of = 261.5 cm consistent with analyses of the vibrational level structure.