Non-resonant and resonant multiphoton ionization of (NO)n and ArnNO clusters with picosecond laser pulses

Abstract

High peak power laser pulses have been used to effect multiphoton ionization (MPI) in supersonic nozzle expansions of nitric oxide in argon. The (NO)_n⩽5 clusters have been detected for the first time by a multiphoton laser technique. The Ar₂ and Ar_n⩽7NO complexes were also observed. Results from a number of different visible and ultraviolet wavelengths are compared and interpreted with references to the known electronic states of (NO)_n and (NO)⁺_n.

When resonant with the dissociative B₁ state of (NO)₂ at ca. 217 nm, cluster ions are observed with picosecond but not with nanosecond laser pulses. In contrast, non-resonant MPI at certain wavelengths results in parent cluster ions with either nanosecond or picosecond lasers. The use of such high-peak-power lasers for the characterization of cluster beams is discussed and compared with more conventional electron-impact techniques.