Dissociative excitation transfer in the reaction of O2(a1Δg) with OH-(H2O)1,2 clusters

Rate constants for the dissociation of OH-(H2O) and OH-(H2O)(2) by transfer of electronic energy from O-2(a(1)Delta(g)) were measured. Values of 1.8x10(-11) and 2.2x10(-11) cm(3) molecule(-1) s(-1), respectively, at 300 K were derived and temperature dependences were obtained from 300 to 500 K for OH-(H2O) and from 300 to 400 K for OH-(H2O)(2). Dissociative excitation transfer with OH-(H2O) is slightly endothermic and the reaction appears to have a positive temperature dependence, but barely outside the uncertainty range. In contrast, the reaction of OH-(H2O)(2) is exothermic and appears to have a negative temperature dependence. The rate constants are analyzed in terms of unimolecular rate theory, which suggests that the dissociation is prompt and is not affected by collisions with the helium buffer gas.