SPATIAL PROFILES OF EFFUSIVE MOLECULAR-BEAMS AND THEIR DEPENDENCE ON GAS SPECIES

The spatial profiles of molecular beams formed by both single and multicapillary sources have been investigated for He, Ne, Ar, Kr, H-2 and N2. The profile measurements were undertaken at distances from the source exit and driving pressures which are typical of those used in atomic collision experiments (1-5 mm and 0.02-10 Torr respectively). The experimental results indicate the clear superiority of a capillary array source over a single tube source, of similar overall dimensions, in producing a well collimated molecular beam over a wide range of driving pressures and distances from the capillary exit. They also indicate that there is a measurable dependence of the beam profile on gas species, particularly at the higher pressures studied. The significance of this result for the relative flow, cross section normalization technique is discussed.