SELECTED-ION FLOW DRIFT-TUBE STUDIES OF THE REACTIONS OF SI-2) WITH HCL, H2O, H2S, AND NH3 - REACTIONS WHICH PRODUCE ATOMIC-HYDROGEN((P)

The reaction rate coefficients. k, for the reactions of ground-state S i+(P-2) with HCl, H2O, H2S, and NH3, have been measured as a function of reactant ion/reactant neutral center-of-mass kinetic energy, KE(CM) , in a selected ion flow drift tube (SIFDT) apparatus, operated with h elium at a temperature 298+/-2 K. The values k of the studied reaction s have very pronounced, negative energy dependencies; the rate coeffic ients decrease by about 1 order of magnitude as KE(CM) increase from n ear thermal values to similar to 2 eV. The results are interpreted in terms of a simple model assuming the reactions to proceed via the form ation of long-lived complexes, These intermediate complexes decompose back to reactants or forward to products, the unimolecular decompositi on rate coefficients for these reactions being k(1) and k(2), respecti vely, It is found that a power law of the form k(-1)/k(2)=const(KE(CM) )(m) closely describes each reaction. (C) 1995 American Institute of P hysics.