Spin–orbit state-selected reactions of Xe+(2P3/2 and 2P1/2) with H2, D2, and HD

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Abstract
Spin–orbit state-selected reactions of Xe+(2PJ ), J=3/2 and 1/2, with isotopic molecular hydrogen (H2, D2, and HD) to form XeH+ and XeD+ are studied using guided ion beam mass spectrometry. Reaction cross sections are determined as a function of reactant kinetic energy from near thermal energy to 15 eV c.m. Although the reaction of Xe+(2P1/2)+H2 to form ground state products XeH++H is exothermic, no reaction is observed at low energies and the reaction cross section is zero or small at higher energies. The Xe+(2P3/2)+H2 reaction has an apparent threshold near its endothermicity, but the cross section rises slowly above this threshold. The reaction energetics and isotope effects indicate two separate mechanisms for Xe+(2P3/2). The dominant mechanism is a direct, impulsive process with an apparent activation barrier. The second mechanism allows reaction near the thermochemical threshold and involves more interaction among all three atoms. These results are interpreted in relation to the spin–orbit coupled potential energy surfaces of XeH+2 system.