Laser probing of product-state distributions in thermal-energy ion–molecule reactions

Abstract

Vibrational and rotational product-state distributions are determined for thermal-energy charge-transfer reactions and Penning ionization processes using laser-induced fluorescence detection in both a flowing afterglow apparatus and a single-collision molecular beam device. The reactions investigated are the charge transfers between N⁺+ CO, Ar⁺+ N₂, Ar⁺+ CO, and the Penning ionization of N₂ by Ne(³P₂). Vibrational distributions provide direct information on major features of the dynamics, such as whether a Franck–Condon mechanism is dominant, whether collision complex formation is important, or if selective vibrational passageways exist between the electronic potential-energy surfaces. The rotational distributions show a variety of additional discriminating dynamical effects, including corroborating evidence for Franck–Condon channels, pinpointing separate mechanisms for different vibrational product states and detecting microscopic bimodalities within individual vibrational levels, which are indicative of multiple entrance- or exit-channel pathways.