Multiphoton ionization and ab initio calculation studies of the hydrogen-bonded clusters C4H5N-(H2O)(n)

The multiphoton ionization of the hydrogen-bonded clusters C4H5N-(H2O)(n) w as studied using a time-of-flight mass spectrometer at the laser wavelength s of 355 and 532 nm. At both wavelengths, a series of C4H5N(H2O)(n)(+) and the protonated C4H5N-(H2O)(n)H+ were obtained. The two-photon resonance ion ization processes at 355 nm make this wavelength produce obviously more abu ndant ions of pyrrole and the clusters than 532 nm. Ab initio calculations show that in the protonated products, the proton prefers to link with the a lpha-C of pyrrole rather than with the N atom. The production of the proton ated products requires an intracluster proton transfer reaction. The proton ated products obtained at 532 nm are suggested to arise from an intracluste r penning ionization or a charge transfer process. The abnormally higher in tensities of C4H4N-(H2O)(n)(+) (n greater than or equal to 1) than those of C4H4N+ are attributed to the stabilization effects of the cluster formatio n on the dissociation products C4H4N+ of the pyrrole molecule.