Investigations on mixed water-clusters: Gas phase titration with cyclopentanone and identification of some isomers by time-of-flight mass spectrometry

Mixed-clusters of water with cyclopentanone have been investigated using high resolution time-of-flight mass spectrometry. These clusters are synthesized in a gas-aggregation source at comparatively higher temperature. They contain water-cluster at the core and cyclopentanone molecules hydrogen bonded through ketone oxygen with the dangling OH available at the core. Thus these mixed-clusters may also be considered as the products of a titration in gas phase. The growth reaction reveals that all clusters are protonated. From the configuration of dimer and tetramer, it is suggested that the proton resides as an Eigen ion in the core. The protonated mixed-clusters containing six, seven and eight water molecules substantiate the hydronium contained hexa, hepta and octamer water-cluster structures predicted by [KJ(H3O)+] model calculations. For clusters with 9-19 water molecules, the core appears to have configurations that give less than the predicted number of dangling bonds. In large size clusters having more than 20 water molecules, the water-core appears to have open configuration like the melted structures obtained as a result of increase in temperature.