Knudsen cell mass spectrometry using restricted molecular beam collimation. I. Optimization of the beam from the vaporizing surface

Abstract

This difference is attributed to the previously approximate assumption that optimizing the restricted collimation solid angle automatically optimizes the sampling of the effused beam included in the restricted collimation angle. Moreover, the location of the evaporating surface for molecules traveling through the collimation device towards the ionization chamber remains an important factor: the distance between the sample evaporation surface and the field aperture is of paramount importance as it changes the molecular transmission to the mass spectrometer or to any target collection device in the conventional Knudsen method.

Monte Carlo simulation of a Knudsen effusion mass spectrometer sampling system

“…The Monte Carlo calculations are about 3.5 at most lower than the analytical calculations of Chatillon and coworkers . The lack of smoothness in the Monte Carlo curve may be due to the relatively small sample size.…”

“…The geometry they used was reproduced as close as possible for this calculation. The diameters of the two apertures are correlated due to the integration over the umbra, as described by Nuta and Chatillon . These are listed in Table along with the transmission factors.…”

“…In Chatillon's method the integration over the penumbra/umbra does not capture the full cross‐section of the orifice. This is important in their most recent calculations . Our method needs further refinement with larger sample sizes and consideration of scattering by background gases.…”

“…Recently, Chatillon and coworkers have discussed a novel method of sampling from a Knudsen cell . Their method is termed "restricted collimation" and involves two collimating apertures above the cell effusion orifice.…”

Erratum to: “Knudsen cell mass spectrometry using restricted molecular beam collimation. I. Optimization of the beam from the vaporizing surface”

“…We correct an error made in a recent paper in this journal. [1] In our original paper, the distance between the vaporizing surface of the sample and the first collimating aperture in Knudsen Cell Mass Spectrometry (KCMS), which is noted as H 1 , was not correctly taken into account during calculations when using Eqn. (12) in that paper.…”