Observation of Magic Numbers for (ROH)nH3O(+) Heteroclusters (R=CH3, CH3CH2,(CH3)2CH and CH3CH2CH2): Implications for Cluster Ion Structure

摘要

We report in this paper nearly identical ion intensity distribution curves forROH/water heterocluster ions for a variety of alcohols. The cluster ions (ROH)9(H20)H+ and (ROH)l0(H20)2H+ were found to display enhanced stability for all of the alcohols studied. Heteroclusters with n < 7 could not be observed upon ionization of neat alcohol clusters and were generally found with low intensity fro the mixed alcohol/water clusters. We will introduce in this paper a structural model which can account for both the stability of the (ROH)9(H20)H+ ions and the loss of water from clusters with n < 7. This model implies a proton switch at a specific cluster size, leading to what may be thought of as a central H30+ ion completely solvated by a ring (or chain) of hydrogen-bonded alcohols. The stable structure formed for (ROH)9(H20)H+ consists of three fused five-membered rings, each consisting of 4 ROH's and a H30+ hydrogen-bonded together. This structure is closely related to that proposed by Castleman and coworkers for the dodecahedral water cluster ((H20)21H+).