Non-maxwellian velocity distributions in the transition region of supersonic expansions of the noble gases He, Ne and Ar

How does the molecular velocity distribution affect kinetics measurements by time‐resolved mass spectrometry?

“…If one assumes that the molecular beam is in the limiting collisionless region for most of the transit from source to detector, the final beam temperatures and velocities may be employed. For on-axis detection (cos θ = 1), generalization to the commonly used two-temperature parameterization [19,22] of the final distribution function should yield similar results to the continuum flow expression used here, because the distortion of the time profile is related to the parallel velocity component. Substituting the displaced Boltzmann distribution into (1) yields [21] n( x, t)…”

“…Most mass spectrometers are density detectors, but for flux detectors the expression for Q must be multiplied by the speed v = | v| (or possibly a power of v [19]) to represent the flux distribution at x. The description of the effect of thermal velocities on the time behavior of the molecular flux for an effusive beam, and the resulting range of validity for kinetic measurements, has been discussed by Moore and Carr [1].…”

Parallel temperatures in supersonic beams: Ultracooling of light atoms seeded in a heavier carrier gas

“…In his simulations, P. A. Skovorodko has found that the distribution of the perpendicular velocity of lithium differs very much from a Maxwellian distribution and is almost perfectly exponential. The fact that the velocity distribution of the perpendicular degree of freedom cannot be Maxwellian was analyzed in detail by Beijerinck and co-workers who suggested to call blistering this effect [11,25]. This effect cannot be taken into account by the theory described in the present paper as the assumption of an elliptic Maxwellian velocity distribution is the starting point of the solution of Boltzmann equation.…”

A Simple Nozzle Configuration for the Production of Low Divergence Supersonic Cluster Beam by Aerodynamic Focusing

“…The reason for choosing this criterion is that in the experiment the clusters passing through the skimmer and reaching the substrate are seen to come from a circular region having a small radius at the nozzle outlet. This region, de ned as the "virtual source" (Bergmann et al 1978;Beijerinck et al 1983), is found to have a diameter of 75 ¹m for a focused beam and of 190 ¹m for an unfocused one . A value of 150 ¹m is thus chosen as representative of the diameter of the locus from which the particles found in the beam should originate (Bergmann et al 1978).…”