VECTOR CORRELATION STUDIES OF HO2 PHOTODISSOCIATION AT 220 NM

The 220 nn photolysis of the hydroperoxyl radical, HO2, is investigate d by probing the ejected OH fragments using Doppler and polarization s pectroscopy. Analysis of the measured line profiles reveals that the O H fragments are predominately (84%) formed with the partner oxygen ato m in its electronically excited D-1 state with a smaller component (16 %) being associated with oxygen atoms in the P-3 ground electronic sta te. Measurement of OH fragment internal state distribution indicates t hat the 23 200 cm(-1) of available energy is primarily released as ele ctronic excitation of the oxygen atom (f(el)=0.57) and to a lesser ext ent as relative translation of the products (f(tr)=0.41). The internal degrees-of-freedom of the OH fragment receive very little of the avai lable energy and are found to be fairly cold (f(vib) < 0.004 and f(rot ) = 0.014). For the primary O(D-1) dissociation channel the measured [ mu . v] correlation is strongly positive (beta(mu upsilon)=0.61) indic ating a preference for parallel alignment of the electronic transition moment and the recoil velocity vector in HO2, consistent with the exc ited state being of A '' symmetry. All other bipolar moments are close to zero for this pathway (beta(mu J)=-0.10, beta(upsilon J)=-0.04, be ta(mu upsilon J)=-0.06) independent of the probed rotational quantum s tate of the OH fragment. For the minor O(P-3) pathway a comparable set of bipolar moments is obtained. An investigation into the source of O H fragment rotation reveals that the combined contributions from out-o f-plane rotation, generated by initial parent thermal motion about A - inertial axis, and in-plane rotation, generated by the combination of bending mode zero-point energy and final state interaction on the exci ted potential energy surface, result in negligible [v . J] correlation in the photodissociation of a thermally distributed sample of HO2 at 300 K. (C) 1996 American Institute of Physics.