Boltzmann equation analysis of a pulsed molecular beam under non-equilibrium conditions

Abstract

Time-of-flight spectra of He and Ar beams produced with a pulsed beam source of short open time (≈50 μs) are investigated as a function of the distance from the nozzle both experimentally and theoretically. The beam is found to be under non-equilibrium conditions even at a distance of longer than 1 m. The observed decrease of the contribution from slow molecules is explained on the basis of the Boltzmann equation with the effect of collisions within the beam.