Vector correlations in dissociative photoionization of O-2 in the 20-28 eVrange. I. Electron-ion kinetic energy correlations

Imaging and time resolved coincidence techniques are combined to determine ion-electron (V-O(+),V-e,P) velocity vector correlations in dissociative ph otoionization (DPI) of the O-2 molecule induced by linearly polarized synch rotron radiation (P). The ion-electron kinetic energy correlations identify each DPI process by its reaction pathway, intermediate molecular state and dissociation limit. The 4 pi collection of ions and electrons provides the ir branching ratios. Up to 12 DPI processes are identified in the 20-28 eV range. Photoionization into the O-2(+)(B (2)Sigma (-)(g)) in the Franck-Con don (FC) region populating the [O+(S-4)+O(P-3)] limit is the dominant proce ss. In the 22.3-24 eV region excitation of the O-2*(3 (2)Pi (u),ns sigma (g )) Rydberg series, followed by dissociation and atomic autoionization to th e [O+(D-2)+O(P-3)] limit reaches about 10% of the DPI flux. A new DPI proce ss is identified in the same energy range, which populates the [O+(S-4)+O(D -1)] limit. At higher energies the relative weight of the four distinct pro cesses which correspond to ionization into the O-2(+)(3 (2)Pi (u)) and O-2( +)(c (4)Sigma (-)(u)) states in the FC region and population of distinct ex cited limits is evaluated. The spatial analysis of the (V-O(+),V-e,P) vecto r correlation for selected processes will be discussed in a companion paper . (C) 2001 American Institute of Physics.