Quantum-mechanical effects in high-expansion jets

Velocity chopping and time-of-flight methods in the measurement of the velocity distribution of particles belonging to a cold supersonic expanding jet are described briefly, quantum-mechanical (QM) effects accompanying the large de Broglie wavelength of the particles and their low average relative energies in the final stage of the expansion are discussed briefly, and data predicted from classical theory are compared. It is concluded that QM effects cannot be discounted in the case of high-expansion cold supersonic jets, and that QM-based prediction fits empirical data closely when the product of jet diameter and inlet pressure is higher than 150 torr cm. The resolution of scattering experiments with beams of neutrals can be improved substantially by using the cold supersonic expanding jets.