Electronic and infrared spectroscopy of [benzene-(methanol) _n]⁺ (n = 1-6)

The microsolvation structure of the [benzene-(methanol)_n] ⁺ (n = 1-6) clusters was analyzed by electronic and infrared spectroscopy. For the n = 1 and 2 clusters, further spectroscopic investigation was carried out by Ar atom attachment, which has been know as a useful technique for discriminating isomers of the clusters. The coexistence of multiple isomers was confirmed for the n = 1 and 2 clusters, and remarkably, preferential production of the specific isomers occurred in the Ar attachment. The most stable isomer of the n = 1 cluster was suggested to be of the "on-ring" structure where the nonbonding electrons of the methanol moiety directly interact with the π orbital of the benzene cation moiety. This is a sharp contrast to [benzene-(H₂O)₁]⁺, exhibiting the "side" structure, where the water moiety is bound to the C-H sites of the benzene cation moiety. The structure of the n = 2 cluster was discussed with the help of density functional theory calculations. Spectral signatures of the intracluster proton-transfer reaction were found for n ≥ 5. The intracluster electron-transfer reaction leading to the (methanol) _m⁺ fragment was also seen upon vibrational and electronic excitation of n ≥ 4.