EXPERIMENTAL-STUDY OF THE REACTIONS OF SI-2) IONS WITH SEVERAL SMALL ORGANIC-MOLECULES AT NEAR THERMAL ENERGIES((P)

The kinetics of the reactions of ground state silicon ions Si+(P-2) Wi th C2H6, CH3OH, and CH3CH2OH has been investigated using a Selected Io n Flow Drift Tube technique (SIFDT). The reaction rate coefficients an d the product distributions have been determined as functions of the r eactant ion/reactant neutral average centre-of-mass kinetic energy (E- CM). The reactions studied are fast at thermal and near thermal energi es and the reaction rate coefficients decrease by nearly one order of magnitude with E-CM increasing up to a few eV. It is shown that the en ergy dependences of the measured reaction rate coefficients can be des cribed by the function of the form k approximate to 1/[1 + (E-CM/E-CM1 )(m)], where E-CM1 and m are parameters which can be determined from t he experimental data. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-liv ed complexes. These intermediate complexes decompose with unimolecular rate coefficients k(-1) and k(2) back to the reactants and forward to the products, respectively. The ratios k(-1)/k(2) can be approximated for reactions studied by a power law function k(-1)/k(2) proportional to (E-CM)(m).