TIME-RESOLVED MOLECULAR-BEAM CHARACTERISTIC IN A PULSED SUPERSONIC JET

A pulsed molecular beam source having short pulse duration (typically 70 ys) and narrow velocity distribution (Delta upsilon/upsilon similar or equal to 8 % for helium) has been constructed utilizing a commercial fuel injector. Beam characteristics of helium and ammonia seeded in helium expansions are accomplished by the use of an electron impact time-of-flight mass spectrometer. The comparisons between experimental data and theoretical calculations show that the proper beam speed is important to predict the evolution of stream temperature and valve shutter function. The decreasing tendency of pulse duration with increasing cluster size leads to the conclusion that the cluster beam property is described as a function of cluster mass and disinct cluster temperature.