TRANSLATIONAL ENERGY-DEPENDENCE OF CROSS-SECTIONS FOR REACTIONS OF OH-(H2O)(N) WITH CH3CL AND CH3BR

A tandem mass spectrometer has been used to measure cross sections and product distributions for reactions of the selectively solvated anion s OH-(H2O)(n) with the neutral molecules CH3Cl (n = 0, 1, or 2) and CH 3Br (n = 0 or 1) over the relative energy range 0.1-5 eV. The reaction s observed include nucleophilic displacement, proton transfer, and col lision-induced dissociation. With the unhydrated reactant ion OH-, the exoergic nucleophilic displacement channel dominates at low energy, a nd the endoergic proton transfer channel competes effectively at energ ies above threshold. Increasing hydration of the reactant ion decrease s both nucleophilic displacement and proton transfer, the latter drast ically, leaving collision-induced dissociation as the major process ab ove 1 eV.