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 infrar ed spectroscopy. The OH band of methyl salicylate monomer was weak and broa d because of the intramolecular hydrogen bond. Those of the methyl salicyla te moiety in small size hydrogen-bonded clusters with various solvent molec ules, such as methyl salicylate-(H2O)(n) (n = 1 and 2), -CH3OH, and -NH3, a lso showed similar characteristics, indicating that the intramolecular hydr ogen bond is retained even in the clusters. The opposite behavior of the di rection of the electronic transition frequency shift and the OH stretching frequency shift was seen between the clusters with the acidic (water and me thanol) and basic (ammonia) solvents. Structures for these clusters are dis cussed on the basis of the frequency shifts of the OH bond.