ESR investigation of the photoisomerization of OClO to ClOO in an H2SO4 glass: Magnetophotoselection and kinetics

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Abstract
The photoisomerization of OClO (ClO2) to ClOO in a sulfuric acid glass at 20 to 77 K has been reinvestigated using electron spin resonance(ESR) to observe the reactant and product and to quantitatively determine their relative concentrations. Polarized light photolysis yields a partial orientation of the remaining ClO2 molecules (magnetophotoselection) and shows that the optical transitiondipole moment lies in the molecular plane and is perpendicular to the ClO2 rotational symmetry axis, as expected for the well known Ã(2 A 2)←X̃(2 B 1) transition of ClO2. Here, however, the photolysis yields only ClOO, in contrast to the gas phase where ClO is observed suggesting photodissociation. The photoisomerization kinetics are nonexponential and suggest that random variations among the ClO2trapping sites in the H2SO4 glass have a considerable effect on the probability that a photoexcited ClO2 molecule will isomerize.
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