Experimental study of the reactions of Si+(2P) ions with several small organic molecules at near thermal energies

The kinetics of the reactions of ground state silicon ions Si⁺(²P) with C₂H₆, CH₃OH, and CH₃CH₂OH has been investigated using a Selected Ion Flow Drift Tube technique (SIFDT). The reaction rate coefficients and the product distributions have been determined as functions of the reactant ion/reactant neutral average centre-of-mass kinetic energy (E _CM). The reactions studied are fast at thermal and near thermal energies and the reaction rate coefficients decrease by nearly one order of magnitude withE _CM increasing up to a few eV. It is shown that the energy dependences of the measured reaction rate coefficients can be described by the function of the formk ≈ 1/[1+ (E _CM/E _CM1) ^m ], whereE _CM1 andm are parameters which can be determined from the experimental data. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived complexes. These intermediate complexes decompose with unimolecular rate coefficientsk _?1 andk ₂ back to the reactants and forward to the products, respectively. The ratiosk _?1/k ₂ can be approximated for reactions studied by a power law functionk _?1/k ₂ ∞ (E _CM) ^m .