Guided-ion beam studies of the reactions of protonated water clusters, H(H2O)+n (n=1–4), with acetonitrile

Reactions of protonated water clusters, H(H2O)n+ (n=1–4), with acetonitrile are studied by using guided-ion beam mass spectrometry. Absolute reaction cross sections are determined as a function of the collision energy from thermal energy to over 10 eV. Proton transfer, charge transfer, and dissociative proton transfer are the reactions seen for n=1. For n=2–4, proton transfer is accompanied by solvent transfer such that the dominant product at low collision energies is H(CH3CN)(H2O)n−1+ in each case. At higher collision energies, additional water ligands are lost and the collision-induced dissociation products, H(H2O)n-m+ where m=1 to n−1, are also observed. The total reaction cross sections are large and decrease slightly with the number of water molecules. The results indicate that energy transfer in these complexes is efficient and thus are consistent with reactions that proceed via hydrogen-bonded intermediate complexes.