Multiphoton ionization of jet-cooled nickelocene with tunable nanosecond laser pulses

Abstract

Abstract Efficient multiphoton ionization of nickelocene molecules in a supersonically cooled molecular beam has been performed for the first time with a nanosecond tunable dye laser operating in the 35,000-cm−1 region which corresponds to the lowest Rydberg transition observed in the one-photon absorption spectrum. The time-of-flight mass spectra obtained show strong signals of intact molecular ions Cp2Ni+ (Cp=η5-C5H5) and weaker peaks of fragment ions CpNi+. The conditions have been found for generation of Cp2Ni+ as the only ionic product of multiphoton excitation. The ion signal dependence on the laser intensity and the resonance-enhanced multiphoton ionization spectrum measured at the mass of Cp2Ni+ testify for saturation of absorption and/or ionization steps at the laser pulse intensities used (2–6 MW cm−2). Possible mechanisms of multiphoton processes resulting in formation of the ions observed are discussed.