THE PHOTODISSOCIATION DYNAMICS OF OCLO BETWEEN 306 AND 370 NM - FRAGMENT TRANSLATIONAL ENERGY-RELEASE AND RECOIL ANISOTROPY

The photodissociation OClO((A) over tilde (2)A(2))-->ClO((X) over tild e(2)II)+O(P-3) was studied at wavelengths between 306 and 370 nm using photofragment translational energy spectroscopy. The flight time dist ributions and anisotropies of the recoiling fragments were measured wi th the photolysis wavelength tuned to 10 maxima of the structured abso rption spectrum, corresponding to a vibronic excitation of the parent molecule with 9-18 quanta in the symmetric stretching coordinate on th e (A) over tilde(2)A(2) surface, The translational energy distribution s show that the ClO fragments are created in highly inverted vibration al state distributions which become extremely broad [v(Cl-O)similar to 1-15] with increasing excitation energy. The large fraction of vibrat ionally hot ClO fragments produced-particularly at lambda<325 nm-could enhance various thermodynamically unfavorable atmospheric reactions i n connection with ozone depletion, The main mechanistic features of th e 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 firs t approximation, as vibrational predissociation on the (A) over tilde (2)A(2) potential energy surface involving a relatively late exit barr ier. From the measured translational energies the barrier height is es timated to be about 48 kJ/mol. (C) 1997 American Institute of Physics.