A STUDY OF MOLECULAR INTERACTIONS IN MOLECULAR BEAMS ISOLATED FROM THE EXHAUST OF SUPERSONIC NOZZLES

Abstract

In high density molecular beams, such as those isolated from supersonic nozzles, collisions between beam molecules may have an important effect on the beam behavior. This paper uses the classical kinetic theory to discuss the effect of these collisions on the intensities and velocity distributions in a beam. Initially, intensities are calculated assuming unchanging Maxwellian velocity distributions. However, the beam collisions will, in fact, alter the velocity distributions in a way that could be described as an "asymmetric cooling" of the beam; a start has been made on examining the effects of this phenomenon.In the case of beams of mixed composition, the analysis indicates that an enrichment of the heavier component will take place as a result of collisions within the beam.Formulae relating beam density profiles to the geometry of the beam-defining elements are also deduced. Numerical examples are worked out for an illustrative case in which the diameter of the beam diaphragms is 0.1 cm and the distance between them is 10 cm, assuming the beam to be isolated from the exhaust of a 7.5 mach expansion with a stagnation temperature of 300° K.