The direct near ultraviolet absorption spectrum of the à 2A2←X̃ 2B1 transition of jet-cooled chlorine dioxide

Abstract

The direct absorption spectrum of the à 2A2←X̃ 2B1 transition of jet-cooled OClO is reported in the 21 000–33 000 cm−1 region. As a result of the rotational cooling afforded by the jet, the upper state level structure has been measured and analyzed in the absence of much of the spectral congestion present in the static gas spectrum. This cooling, in addition to the sensitivity and resolution of the interferometric detection, results in accurate determinations of frequencies and relative absorption intensities. All of the vibrational modes are observed in the 2A2 spectrum with unusually large intensities in the even quanta of the asymmetric stretch. A complete reanalysis of the spectrum yields new 2ν3 and 4ν3 energies of 886.8 and 1855.8 cm−1, respectively. The present assignment is supported by relative intensity and anharmonicity comparisons. We have reconsidered the issue of the intense even ν3 activity in terms of a double-minimum potential in the Q3 coordinate adjusted for the new energies of the asymmetric stretch. The results of this fit agree with experimental relative intensity and isotope measurements. The potential involves a C2v barrier height of 1153 cm−1 with a 0+–0− inversion splitting of 127 cm−1. This value is consistent with the 001 energy determined indirectly from anharmonicity-induced Coriolis perturbations present in the low energy (v1,0,0) levels assumed to be caused by (v1−1,2,1) interactions.