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The direct absorption spectrum of the A 2A2←X 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. [ABSTRACT FROM AUTHOR]

This paper presents the A 2A2←X 2B1 direct absorption spectrum of OClO recorded at rotational resolution in a cold molecular jet. Rotational temperatures as low as 30 K are achieved and result in substantial reduction of the inhomogeneous effects that congest the room temperature spectrum. No direct spectroscopic evidence is found for the 2A1←X 2B1 perpendicular transition which was previously thought to be hidden under the stronger A 2A2←X 2B1 parallel transition. All of the modes of the 2A2 state observed display homogeneous rotational linewidth broadening. This broadening, due to the efficient excited state chemistry of the 2A2 state, is measured and modeled for the vibrational bands involving (v1,0,0), (v1,1,0) and (v1,0,2) for v1=4–10. We confirm the lack of rotational state dependence on the predissociation within a given vibrational band by a comparison of the linewidths obtained here at low J and K with those known at high J and K. For a given symmetric stretch band, the linewidths associated with both of the corresponding combinations of ν1 with the bend and asymmetric stretch are always greater than the symmetric stretch alone. Because of this and in view of the substantial drop in frequency of both ν2 and ν3 upon the transition we discuss the possible involvement of these modes with regard to the photoreactivity of the 2A2 state. In particular, from the higher energy lifetime information obtained here and the available photoproduct information, we address the dynamics of OClO in the 2A2 state with respect to couplings to both the 2A1 and 2B2 close-lying excited states. [ABSTRACT FROM AUTHOR]