Association reactions of trimethylsilyl ions

Abstract

AbstractAdduct ions, [M + (CH3)3Si]+, were produced by bimolecular association reactions of trimethylsilyl ions, (CH3)3Si+, with acetone, cydohexaoone, anisole, dimethyl ether, 2,5‐dimethylfuran, 2‐methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ∼10−7 Torr (1 Torr = 133.3 Pa). The rate constants, ka, for the association reactions varied from 100% to 2% of the collision rate constants, kc. The rate constants were independent of pressure, except for furan. Measurements were also made of bond dissociation energies for these adduct ions, D[(CH3)3Si+–X], from equilibrium measurements. The association efficiency, ka/kc, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative agreement with theoretical predictions. Observations pertinent to the dependence of ka on reactant temperature and relative kinetic energy are discussed. The possibility of determining ion‐neutral complex binding energies from radiative association rate constants is considered.