Imaging of supersonically expanded and pulsed molecular beams by nonlinear photoionization processes

摘要

In molecular spectroscopy, imaging of supersonically expanded and jet-cooled molecular pulses to evaluate their time of flight and velocity is useful in obtaining photoionization spectra of higher resolution, well-resolved, and enhanced signal to noise ratio. In this paper, the ultraviolet output of frequency doubled OPO laser at 266 nm was employed to obtain highly-resolved (2+1) resonance-enhanced multiphoton ionization (REMPI) spectra for cooled molecular pulses of methyl iodide (CH3I) sample seeded in helium gas. The recorded photoionization spectra were manipulated to study the shape, duration and structure of the jet cooled molecular beam pulses. A two meter time- of- flight (TOF) mass spectrometer was employed to identify and record the ions produced while varying the time delay between molecular pulses and laser shots. Imaging of CH3I molecular pulses yielded lorentzian distributions of full width at base and flight time peak location corresponding to pulses duration of ～ 0.3 milliseconds and 931 m/s cooled molecules translational velocity, respectively.