Molecular Beam Sources Fabricated from Multichannel Arrays. V. Measurement of the Speed Distribution

Abstract

A technique for measuring the speed distribution of molecular beams which uses symmetric modulation and phase-sensitive detection is described. Corrections for system errors on experiments of this type are developed and verified. In addition to the expected 1/v dependence of the ionizer, the extraction efficiency of the quadrupole mass spectrometer detector is shown to depend on the velocity of the molecules before ionization. The prediction of 5.5% energy enhancement of beams from channel sources operated at pressures well above the free-molecule flow limit has been verified.