Photodissociative ionization in the 21–41 eV region: O 2, N 2, CO, NO, CO 2, H 2O, NH 3 and CH 4

Abstract

Branching ratios have been measured for the photodissociative ionization of O 2, N 2, CO, NO, CO 2, H 2O, NH 3 and CH 4 between 16.8 and 40.8 eV, using line sources. Inconsistencies in previous photoionization fragmentation patterns for NO and H 2O at 21.2 eV, and for CH 4 at 16.8 eV, have been clarified. The high energy state of CO + has been found to decay predominantly to O + + C, in contrast to a recent study. Partial cross sections for formation of high energy states in O 2 + and CO 2 + deduced from this study are substantially lower than those reported in a recent 304 Å photoelectron spectroscopic investigation. The NO + decomposition at higher energy favors N + + O, although the lower energy channel is O + + N. Ionization from the inner (2s-like) valence states of CO 2 and H 2O leads to C + and O + fragments, respectively, with probable shattering of the molecular ion into atomic and ionic fragments.