Infrared Spectroscopy of Intramolecular Hydrogen-Bonded OH Stretching Vibrations in Jet-Cooled Methyl Salicylate and Its Clusters

The OH stretching vibration of methyl salicylate and its solvated clusters in a supersonic free jet was observed by using fluorescence-detected infrared spectroscopy. The OH band of methyl salicylate monomer was weak and broad because of the intramolecular hydrogen bond. Those of the methyl salicylate moiety in small size hydrogen-bonded clusters with various solvent molecules, such as methyl salicylate−(H 2 O) n ( n = 1 and 2), −CH 3 OH, and −NH 3, also showed similar characteristics, indicating that the intramolecular hydrogen bond is retained even in the clusters. The opposite behavior of the direction of the electronic transition frequency shift and the OH stretching frequency shift was seen between the clusters with the acidic (water and methanol) and basic (ammonia) solvents. Structures for these clusters are discussed on the basis of the frequency shifts of the OH bond.