The adsorption of methanol on large water clusters

We have studied the adsorption of methanol monomers onto large water clusters by using the pick-up technique to deposit methanol onto water clusters formed in a supersonic expansion of pure water vapour. The clusters are ionised by electron impact and mass analysed. The major low-mass methanol-containing ion peaks (< 100u) correspond to unclustered and unprotonated methanol and have similar cracking patterns to free methanol monomers, although there are some heterocluster ions observed containing no more than one water and two methanol molecules. The measured ion appearance potentials indicate that the methanol is directly ionised. In contrast to previous results for methanol adsorbed onto large argon clusters [F. Huisken and M. Stemmler, J. Chem. Phys. 98 (1993) 7680], we do not find any evidence for the formation of dimers or higher clusters of methanol on the water clusters.