A Versatile Molecular Beam Scattering Apparatus Utilizing Electron Bombardment Detection

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Abstract
A versatile crossed molecular beam apparatus has been designed, fabricated, and tested. The instrument consists of a large cylindrical stainless steel ``scattering chamber'' which contains differentially pumped nozzle‐skimmer and detector chambers. The crossed beams intersect at the cylinder axis. The detector assembly can be rotated about the scattering center from −43 to +133° with respect to the primary beam direction. The scattered intensity is measured using a modified Weiss electron bombardment ionizer with quadrupole mass filter. Over‐all detection efficiency of the system for a thermal argon beam is 0.25%. Background discrimination is effected by means of double modulation (synchronous chopping of both crossed beams with beat frequency lock‐in detection). The apparatus has been employed in studies of the rainbow scattering of Ar by various gases.