THE PURE ROTATION SPECTRUM OF HBR IN THE SUBMILLIMETER-WAVE REGION

The pure rotation spectra of both H79Br and H81Br were recorded at Doppler resolution by means of tunable far-IR (TuFIR) spectroscopy. The hyperfine structure of the rotational lines, due to the presence of the quadrupole moment in the bromine nucleus, was fully resolved. Rotational transitions, ΔJ = +1, ΔF = 0, ±1 were measured and assigned with J ranging from 1 to 9. Forty-four and thirty-nine lines were observed in the region between 1.0 and 4.5 THz for H79Br and H81Br, respectively. These transitions were analyzed on the basis of a Hamiltonian containing terms up to the sixth power in the angular momentum, the first-order quadrupole interaction, and the nuclear magnetic interaction. The obtained spectroscopic parameters, which included the centrifugal distortion dependence of the quadrupole constant, here reported for the first time for a hydrogen halide molecule, reproduce the transition frequencies within the accuracy of the measurements. © 1991.