Determination of nuclear spin-rotation coupling constants in CF3I by chirped-pulse Fourier-transform microwave spectroscopy

The rotational spectrum of CF₃I in the ground vibrational state has been re-measured using a chirped-pulse Fourier-transform microwave spectrometer recently constructed at the University of Bristol. The new spectrometer provides the capability to acquire broadband rotational spectra throughout an operational frequency range of 7-18 GHz. The frequencies of ninety-nine F₁′-F₁″ transitions in three distinct J_K′-J_K″ bands have been recorded during an experiment which required only a couple of hours of data collection. Many of these transitions have additionally been re-measured using a Balle-Flygare, Fourier-transform microwave spectrometer. Fitting the data to the Hamiltonian for a C_3v prolate, symmetric top has allowed the determination of new spectroscopic parameters. The rotational constant, B₀, and nuclear quadrupole coupling constant, χ_aa(I), are consistent with the results provided in earlier works. The nuclear magnetic spin-rotation constants, C_perp.(I) and C_perp.(F), have been independently determined for the first time. These parameters are evaluated as 6.92(5) kHz and 2.37(11) kHz respectively. A technical description of the new CP-FTMW instrument is presented.