Tandem mass spectrometry studies of acetone and acetone/water cluster ions

Ion clusters were formed in a temperature-variable high-pressure ion source from neat acetone and acetone/water mixtures and subjected to tandem mass spectrometry studies-unimolecular and collisionally activated mass-analyzed ion kinetic energy spectroscopy. The predominance of water loss from H(+)(H20)(A) l=3, where A = acetone, suggests that the solvation sphere around H3O(+) does not close at l = 3, contrary to the case of acetonitrile or dimethyl ether. The results may be interpreted in terms of suggested ion structures which involve isomerization enroute to dissociation. The virtual absence of H/D scrambling in the collisionally activated dissociation of H3O(+)(DA)3, DA =acetone-d 6, and of D3O(+)(A)3 means that if enolization takes place, it is a rate-determining step in an irreversible isomerization. The stability of H(+)(H2O)(A)3 is a dominant factor in the observation of acetone loss from H(+)(H20)(A)4.