State-Selected Ion-Molecule Reactions Studied by the Threshold Electron-Secondary Ion Coincidence (TESICO) Technique, Ar+(2P3/2, 2P1/2) + HCl

The reactions of Ar+ with HCl were studied for the two spin-orbit states of Ar+, 2P3/2 and 2P1/2, by the threshold electron-secondary ion coincidence (TESICO) technique. State selected relative reaction cross sections of the two product channels, hydrogen abstraction (HA) to form ArH+, and charge transfer (CT) to form HCl+, were determined at five collision energies in the range of 0.71–3.5 eV. At low collision energies, the cross sections of both channels show no substantial difference between the two spin-orbit states. At high collision energies, the cross sections for the HA channel also show no difference between the two states, whereas those for the CT channel show significant dependence on the spin-orbit state, the cross sections for Ar+(2P1/2) being always larger than those for Ar+(2P3/2). Combining these results with the coincidence time-of-flight (TOF) spectra, a direct reaction mechanism is suggested for both channels. The importance of the nonadiabatic transitions between the surfaces correlating to the Ar+ + HCl and Ar + HCl+(A2Σ) states in leading the reaction is proposed. Proton transfer follows the nonadiabatic transition for the HA channel and radiative or nonradiative transition follows for the CT channel.