Doppler-limited dye laser excitation spectroscopy of HCCl

Abstract

The cw dye laser excitation spectrum of the A ̃ 1A″(050) ← X ̃ 1A′(000) vibronic band of HCCl was observed between 16 539 and 16 656 cm −1 with the Doppler-limited resolution, 0.03 cm −1. The HCCl molecule was generated by the reaction of discharged CF 4 with CH 3Cl. The observed spectra were assigned to c-type transitions with Δ K a = ±1 and also to axis-switching transitions with Δ K a = 0 or −2, but all with K′ a = 0, both for HC 35Cl and HC 37Cl. A rotational analysis yielded the rotational constants and quartic centrifugal distortion constants for the ground vibronic state and the band origin. A weak vibronic band, about one-third as intense as the main band, was found at about 57 cm −1 to the violet of the main band for both isotopic species, and was ascribed to a transition from the ground vibronic state to a vibrational level, possibly (041), of the à state. The rotational levels of HC 35Cl in the à state showed a large perturbation; the J′ = 8, 9, and 10 levels were found to be split into two components. A normal coordinate analysis was carried out to calculate the centrifugal distortion constants and the inertia defect, which were in fair agreement with the observed values. The molecular structure of HCCl in the ground vibronic state was recalculated from the rotational constants of the two isotopic species combined with the 0.75 B 0 + 0.25 C 0 value previously reported for DC 35Cl.