Vector correlations in dissociative photoionization of O2 in the 20-28 eV range.: 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 photoionization (DPI) of the O-2 molecule induced by linearly polarized synchrotron 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 their 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-Condon (FC) region populating the [O+(S-4)+O(P-3)] limit is the dominant process. 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 the [O+(D-2)+O(P-3)] limit reaches about 10% of the DPI flux. A new DPI process 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 processes 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 excited limits is evaluated. The spatial analysis of the (V-O(+),V-e,P) vector correlation for selected processes will be discussed in a companion paper. (C) 2001 American Institute of Physics.