The photochemical dynamics of the à 2A2 state of chlorine dioxide

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Abstract
This paper presents the à 2A2←X̃ 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←X̃ 2B1 perpendicular transition which was previously thought to be hidden under the stronger à 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.

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