St. Arnold et Aa. Viggiano, EFFECT OF ION HYDRATION IN THE GAS-PHASE PROTON-TRANSFER REACTION OF OH- WITH HBR, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(15), 1997, pp. 2859-2861
We have examined the role of solvation on intrinsic ion reactivity by
measuring rate constants for the reactions of OH-(H2O)(n), 0 less than
or equal to n less than or equal to 11, with HBr at 100 K. The reacti
ons all proceed by proton transfer with accompanying solvent transfer.
For 0 less than or equal to n less than or equal to 7, the reactions
proceed at the collisional rate, while rate constants for the larger c
luster reactions decrease slowly with cluster size. The reaction for n
= 11 is only one-third efficient. Product ion distributions were meas
ured for the clusters 0 less than or equal to n less than or equal to
7. For clusters containing two or more solvent molecules, the reaction
s with HBr all yield three product ions of the form Br-(H2O)(m), which
differ only in the degree of solvation of the core ion. The average n
umber of solvent molecules lost during the reaction, represented by [n
- m], increases with increasing cluster size; the value of [n - m] fo
r n = 7 is 3.4. The significant decrease in reaction efficiency at lar
ger cluster sizes is discussed in terms of reaction energetics and pos
sible structural changes within the primary cluster ion series.