Determination of nuclear spin–rotation coupling constants in CF 3I by chirped-pulse Fourier-transform microwave spectroscopy

Abstract

The rotational spectrum of CF 3I 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 F 1′– F 1″ 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, B 0, 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.