Vector correlations in dissociative photoionization of O2 in the 20–28 eV range. I. Electron-ion kinetic energy correlations

Abstract

Imaging and time resolved coincidence techniques are combined to determine ion-electron (VO+,Ve,P) velocity vector correlations in dissociative photoionization (DPI) of the O2 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 4π 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 O2+(B 2∑g−) in the Franck–Condon (FC) region populating the [O+(4S)+O(3P)] limit is the dominant process. In the 22.3–24 eV region excitation of the O2*(3 2∏u,nsσg) Rydberg series, followed by dissociation and atomic autoionization to the [O+(2D)+O(3P)] limit reaches about 10% of the DPI flux. A new DPI process is identified in the same energy range, which populates the [O+(4S)+O(1D)] limit. At higher energies the relative weight of the four distinct processes which correspond to ionization into the O2+(3 2∏u) and O2+(c 4∑u−) states in the FC region and population of distinct excited limits is evaluated. The spatial analysis of the (VO+,Ve,P) vector correlation for selected processes will be discussed in a companion paper.