Photodissociation of O2 via the Herzberg continuum:: Measurements of O-atom alignment and orientation

Irradiation of molecular oxygen O-2 in the region of the Herzberg continuum between 218 nm and 239 nm results in the production of open-shell photofragments O(P-3) + O(P-3). Product O(P-3(j); j = 0,1,2) atoms were ionized using resonantly enhanced multiphoton ionization (2 + 1 REMPI) near 225 nm and the ions collected in a velocity-sensitive time-of-flight mass spectrometer. By controlling the polarization of the photolysis and ionization radiation, we have measured alignment and orientation parameters of O-atom electronic angular momentum ( j) in the molecule frame. The results show alignment from both parallel and perpendicular transitions that are cylindrically symmetric about the velocity (upsilon) of the recoiling O atom. We also observe electronic alignment that is noncylindrically symmetric about upsilon, resulting from coherence between multiply excited dissociative states. Photodissociation with linearly polarized light is shown to produce O atoms that are oriented in the molecule frame, resulting from interference between parallel and perpendicular dissociative states of O-2. Semiclassical calculations that include spin-orbit coupling between six excited states reproduce closely the observed polarization. (C) 2003 American Institute of Physics.