The photodissociation dynamics of OClO between 306 and 370 nm: Fragment translational energy release and recoil anisotropy

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Abstract
The photodissociation OClO(à 2A2)→ClO(X̃ 2Π)+O(3P) was studied at wavelengths between 306 and 370 nm using photofragment translational energy spectroscopy. The flight time distributions and anisotropies of the recoiling fragments were measured with the photolysis wavelength tuned to 10 maxima of the structured absorptionspectrum, corresponding to a vibronic excitation of the parent molecule with 9–18 quanta in the symmetric stretching coordinate on the à 2A2 surface. The translational energy distributions show that the ClO fragments are created in highly inverted vibrational state distributions which become extremely broad [v(Cl–O)∼1–15] with increasing excitation energy. The large fraction of vibrationally hot ClO fragments produced–particularly at λ<325 nm–could enhance various thermodynamically unfavorable atmospheric reactions in connection with ozone depletion. The main mechanistic features of the dissociation process, which account for the almost constant average translational energy and linearly increasing vibrational energy of ClO as a function of the excitation energy, can be interpreted, to a first approximation, as vibrational predissociation on the à 2A2 potential energy surface involving a relatively late exit barrier. From the measured translational energies the barrier height is estimated to be about 48 kJ/mol.