Chemical reactions on clusters. 5. Gas-phase unimolecular decomposition of the methyl alcohol, methyl alcohol-3, methyl-d3 alcohol, and methyl-d3 alcohol-d ions in association with argon and carbon dioxide clusters

Ion clusters of the type Ar/sub n/ x X/sup +/ and (CO/sub 2/)/sub n/ x X/sup +/, where X is one of four isotopic variants of methanol, have been formed by electron impact following the adiabatic expansion of an inert gas/methanol mixture. In the case of argon clusters the product ions Ar/sub n/ x CH/sub 2/OH/sup +/ and Ar/sub n/ x COH/sup +/ (or their isotopic equivalents) are observed. For carbon dioxide clusters the only product ion is (CO/sub 2/) x CH/sub 2/OH/sup +/. A consideration of the available experimental data on the fragmentation pattern of methanol ions, and in particular results from charge-transfer and photoelectron spectroscopy experiments, supports the proposal that cluster-bound methanol ions are excited by charge transfer from the inert gas cluster as opposed to an individual inert gas atom or the ionizing electron. From a knowledge of the internal energy of the methanol ions a lower limit to the vibrational predissociation time has been calculated as 10/sup -12/ s.