Absolute state-selected and state-to-state total cross sections for the Ar+(2P3/2,1/2)+CO2 reactions

Abstract

Absolute spin–orbit state-selected total cross sections for the reactions, Ar+(2P3/2,1/2)+CO2→CO+2+Ar [reaction (1)], CO++O+Ar [reaction (2)], O++CO+Ar [reaction (3)], C++2O+Ar [reaction (4)], ArC++2O [reaction (5)], ArO++CO [reaction (6)], and ArCO++O [reaction (7)] have been measured in the center-of-mass collision energy (Ec.m.) range of 0.26–131 eV. The ratio of the charge-transfer cross section due to Ar+(2P1/2) to that associated with Ar+(2P3/2) varies in the range of 0.5–0.8. The appearance energies observed for CO+ (Ec.m.=4.2±0.5 eV), O+ (Ec.m.=3.7±0.5 eV), and C+ (Ec.m.=12.6±0.5 eV) are in agreement with the thermochemical thresholds for reactions (2), (3), and (4), respectively. The comparison of the absolute cross sections for CO+, O+, and C+ from CO2 by photoionization and by dissociative charge transfer [reactions (2)–(4)] is made. The kinetic-energy analysis of product CO+2, CO+, O+, C+, ArO+, and ArC+ suggests that reactions (2)–(7) proceed via a charge-transfer predissociation mechanism. This experiment, together with the previous studies of Ar+(2P3/2,1/2)+N2(O2,CO), supports the conclusion that product ions formed by dissociative photoionization are also produced by dissociative charge transfer. We find that the absolute cross sections for product ions formed in the dissociative charge-transfer processes [reactions (2)–(4)] are substantially greater than those formed in the dissociative photoionization of CO2, a finding consistent with the general observation that photoionization cross sections are significantly smaller than charge-transfer cross sections. The relative cross sections for CO+, O+, and C+ formed by reactions (2)–(4) are also found to be different from those for photoionization of CO2. This difference is attributed to the anisotropic interaction potential surface responsible for the Ar+(2P3/2,1/2)+CO2 reactions.