Multiphoton Ionization and ab initio Calculation Studies of the Hydrogen-Bonded ClustersC4H5N-(H2O)n

The multiphoton ionization of the hydrogen-bonded clusters C4H5N-(H2O)n was studied using a time-of-flight mass spectrometer at 355nm and 532nm laser wavelengths.At both wavelengths,a series of C4H5N-(H2O)n+and the protonated products C4H5N-(H2O)nH+ were obtained.The two-photon resonance ionization processes at 355nm make the ion intensities of pyrrole and the clusters obviously more abundant than at 532nm.Ab initio calculations show that in the protonated products,the proton prefers to link with α-C of pyrrole rather than with the N atom.The production of the protonated products needs an intracluster proton transfer reaction.The protonated products obtained at 532nm are suggested to arise from an intracluster penning ionization or a charge transfer process.The abnormally higher intensities of photofragments C4H4N-(H2O)n+(n≥1) than C4H4N+ are attributed to the stabilization effects of the cluster formation on the dissociation products C4H4N+ of the pyrrole molecule.