Water-catalyzed hydrolysis of the radical cation of ketene in the gas phase: theory and experiment.

Both theoretical and experimental investigations are reported for the gas-phase hydrolysis of the radical cation of ketene, H(2)CCO(+). Density functional theory (DFT) with the B3LYP/6-311++G(d,p) method indicates that a second water molecule is required as a catalyst for the addition of water across the C=O bond in H(2)CCO(+) by eliminating the activation barrier for the conversion of H(2)CCO.H(2)O to H(2)CC(OH)(2). Theory further indicates that H(2)CC(OH)(2).H(2)O may recombine with electrons to produce neutral acetic acid. Experimental results of flow-reactor tandem mass spectrometer experiments in which CH(2)CO(+) ions were produced either directly from ketene by electron transfer or by the chemical reaction of CH(2)(+) with CO are consistent with formation of an (C(2),H(4),O(2))(+) ion in a reaction second-order in H(2)O. Furthermore, comparative multi-CID experiments indicate that this ion is likely to be the enolic CH(2)C(OH)(2)(+) cation. The results suggest a possible mechanism for the formation of acetic acid from ketene and water on icy surfaces in hot cores and interstellar clouds.