https://doi.org/10.1351/goldbook.M03982
A molecular beam is produced by allowing a gas at higher pressure to expand through a small orifice into a container at lower pressure. The result is a beam of particles (atoms, free radicals, molecules or ions) moving at approximately equal velocities, with few collisions occurring between them. In a crossed molecular-beam experiment a reaction is studied using collimated beams of reactant molecules. For a
bimolecular
reaction, beams of the two reactants are caused to impinge on one another, often at an angle
of 90°. In a beam-gas scattering
experiment a collimated beam is introduced into a gas, and the scattering
patterns are observed.