New insights onto dissociation of state-selected O2+ ions investigated by double imaging photoelectron photoion coincidence: The superimposed 32Πu and c4Σu- inner-valence states.

Abstract

The double imaging photoelectron photoion coincidence technique has been applied to investigate the dissociation of state-selected O2+(32Πu, c4Σu-) ions at hv = 25.4 eV. It is shown that the O2+ ions prepared in the 32Πu inner-valence state can dissociate toward two channels where a distinct changeover from the third dissociation limit O(3P) + O+(2D) to the fifth limit O(3P) + O+(2P) is observed at a binding energy of ∼23.8 eV. Up to four dissociation limits have been identified in the dissociation of the v = 0 vibrational level of the c4Σu- electronic state, and in particular, the products toward the third limit with a very weak intensity are definitely identified and assigned. In addition, the individual contributions of the two superimposed 32Πu and c4Σu- states to the fifth dissociation limit are clearly separated and determined for the first time. The anisotropy parameters of the O+ fragment ion toward different dissociation limits have also been measured and exhibit specific state-selected characteristics. The dissociation mechanisms of the 32Πu and c4Σu- states including predissociation and tunneling motion are proposed based on the present experimental results and the existing theoretical potential energy curves.