Probing branching mechanism through resonance-type oscillation in the collision-energy dependence of Penning ionization reaction of Ar (3P) with oriented CH3I

Abstract

The collision energy and orientation-angle-resolved Penning ionization cross sections were determined for the Ar (3P)+CH3I reaction. A remarkable depletion was recognized in the collision- energy dependence of the orientation-angle-resolved Penning ionization cross section. The depletion could be interpreted as the competitive neutral dissociation from the Rydberg states formed by an electron exchange mechanism related to a 3a1 molecular orbital. The stereo selectivity for the Penning ionization and neutral dissociation were discussed. From the series of our studies on Ar (3P)+CH3X (X=Cl,Br,I) reactions, it was substantiated that the orientation angle and collision-energy-resolved Penning ionization cross section give an important information about the branching mechanism to the Rydberg states that are linked to the neutral dissociation channels.