Velocity map imaging study of the O2 ion-pair production at 17.499 eV:: Simultaneous parallel and perpendicular transitions

The fine structure resolved photofragment O-(P-2(j)) image from the O-2 ion-pair production it 17.499 eV has been recorded. The branching ratio for producing the low energy spin-orbit O (P-2(3/2)) component to the high energy spin-orbit O-(P-2(1/2)) component is 1:0.78 and the optical transitions for them correspond to perpendicular and parallel transitions, respectively. The anisotropy parameters, 1.64 for channel producing O-(P-2(1/2)) and -0.35 for O-(P-2(3/2)), suggest that the dissociation proceeds via the states with symmetry (3)Sigma(-)(u) and 3 Pi(u), respectively. Although the main mechanisms for the O-2 ion-pair production are the predissociation via the intermediate Rydberg states, the direct dissociation mechanism for the channel producing O-(P-2(1/2)) may also be involved.