Multiphoton ionization and ab initio calculation studies of pyridazine–(water)n clusters Original Research Article

The multiphoton ionization of the hydrogen-bonded clusters pyridazine–(water)n (C4H4N2–(H2O)n) was studied using a laser photoionization time-of-flight (TOF) mass spectrometer at the wavelengths of 355 and 532 nm. At both the wavelengths a series of protonated ions C4H4N2–(H2O)nH+ were observed. The results of ab initio calculations show that in the protonated products the proton prefers to link with the nitrogen atom. The dihedral angle formed by the water and pyridazine molecule planes is one of the important factors contributing to the stability of the binary cluster. The protonated cluster ions measured in the experiment may be produced via an intracluster penning ionization or a charge transfer process.