The formation and destruction of H3Ominus;

摘要

We report the first measurements of rate constants for formation and reaction of the hydratedhyphen;hydride ion H3Ominus;. We studied the Kleingeldndash;Nibbering reaction lsqb;Int. J. Mass Spectrom. Ion Phys.49, 311 (1983)rsqb;, namely, dehydrogenation of formaldehyde by hydroxide to form hydratedhyphen;hydride ion and carbon monoxide. The ODminus;+H2CO reaction is about 35percnt; efficient at 298 K, with ODminus;/OHminus;exchange occurring in about half the reactions. H3Ominus;was observed to undergo thermal dissociation in a helium carrier gas at room temperature with a rate constant of 1.6times;10minus;12cm3thinsp;sminus;1. We also studied a new reaction in which H3Ominus;is formed: The association of OHminus;with H2in a He carrier gas at low temperatures. The rate coefficient for this ternary reaction is 1times;10minus;30cm6thinsp;sminus;1at 88 K. Rate coefficients and product branching fractions were determined for H3Ominus;reactions with 19 neutral species at low temperatures (88ndash;194 K) in an H2carrier. The results of ionhyphen;beam studies, negativehyphen;ion photoelectron spectroscopy, and ionhyphen;molecule reaction data allow us to specify the hydridendash;water bond energy D0298(Hminus;minus;H2O)=14.4plusmn;1.0 kcalthinsp;molminus;1(0.62plusmn;0.04 eV). The heat of formation of H3Ominus;, minus;37.5plusmn;1.0 kcalthinsp;molminus;1, and the proton affinity of H3Ominus;, 386.0plusmn;1.0 kcalthinsp;molminus;1, are derived from these results. Dissociation of H3Ominus;into OHminus;and H2requires 4.5plusmn;1.0 kcalthinsp;molminus;1energy.