KINETICS AND MECHANISM STUDIES OF LARGE PROTONATED WATER CLUSTERS, H+(H2O)N, N = 1-60, AT THERMAL-ENERGY

Large protonated water clusters, H+ (H2O)n, n = 1-60, were produced and their reaction kinetics with CH3CN, CH3COCH3, and CH3COOCH3 were studied under thermal conditions in a fast flow reactor. The experimental findings show that the ionization method and temperature are the most crucial factors for producing these large clusters. The results also demonstrate that the attainment of an uniform temperature distribution, limiting the amount of water added into the flow tube, and carefully controlling the heating of the reactant gas inlet are among the important parameters which must be considered in making quantitative measurements of the reaction rate constants. For the case of all three reactants, the measured rate constants agree fairly well with theoretically predicted collision rates within experimental error for the temperature range covered in the experiment, and for the full range of cluster sizes up to n = 60. The reaction mechanisms were found to change from proton transfer to ligand switching, and ultimately to an association process as the cluster size increases.