Folding of the HydrogenBond Network of H+(CH3OH)7with RareGas Tagging.

A number of isomer structures can be formed in hydrogen-bondedclusters, reflecting the essential variety of structural motifs ofhydrogen bond networks. Control of isomer distribution of a clusteris important not only in practical use for isomer-specific spectroscopybut also in understanding of isomerization processes of hydrogen bondnetworks. Protonated methanol clusters have relatively simple networksand they are model systems suitable to investigate isomer distributionchanges. In this paper, isomer distribution of H+(CH3OH)7is studied by size-selective infrared spectroscopyin the OH and CH stretching vibrational region and density functionaltheory calculations. While the clusters produced by a supersonic jetexpansion combined with electron ionization were predominantly isomershaving open hydrogen bond networks such as a linear chain, the Aror Ne attachment (so-called rare gas tagging) entirely switches theisomer structures to compactly folded ones, which are composed onlyof closed multiple rings. The origin of the isomer switching is discussedin terms of thermal effects and specific isomer preference. [ABSTRACT FROM AUTHOR]