crossed-beam reaction

A chemi­cal reaction in which two molecular beams are crossed; one beam is re­garded as the incident beam of gas and the other as the target gas. This technique enables a great deal of in­formation to be gained about the chemical reaction since the states of both the target and projectile mol­ecules can be controlled. The inci­dent beam is characterized by its incident beam flux, I, which is the number of particles per unit area per unit time. The scattered molecules can be detected first by ionizing them and then detecting the ions electrically or using spectroscopy if changes in the vibrational or rota­tional states of molecules in a reac­tion are of interest.