Ion-pair dissociation dynamics of O2 in the range 17.2-17.5 eV studied by XUV laser and velocity map imaging method

The ion-pair dissociation dynamics of O-2, O-2 + hv -> O+(S-4) + O-(P-2(1/2,3/2)), in the photon energy range 17.20-17.50 eV has been studied using extreme ultraviolet laser and velocity map imaging method. The ion-pair yield spectrum and the fine structure resolved photofragment O-(P-2(j)) velocity map images have been recorded. The branching ratios between the two spin-orbit components O-(P-2(3/2)) and O-(P-2(1/2)) and the corresponding anisotropy parameters describing their angular distributions have been determined. It is found that the fragments O-(P-2(1/2)) are all from parallel transitions, while the fragments O-(P-2(3/2)) are from both parallel and perpendicular transitions. The main products for most of the excitation photon energies are O-(P-2(1/2)). The dissociation dynamics has been discussed based on the ab initio potential energy curves of the ion-pairs. The major peaks in the ion-pair yield spectrum have been assigned based on the angular distribution of the photofragments. The experimental results suggest that the so-called strong and weak series of Rydberg states converging to O-2(+) (b(4)Sigma(-)(g)) should have symmetries of (3)Sigma(-)(u) and (3)Pi(u), respectively. In addition to the Rydberg states converging to O-2(+) (b(4)Sigma(-)(g)), the Rydberg states converging to O-2(+) (A(2)Pi(u)) should also play a role in the ion-pair dissociation of O-2. (C) 2013 AIP Publishing LLC.