The formation and quenching processes of triatomie excimers following short duration electron beam excitation of high pressure rare gas halide mixtures have been investigated. Formation of triatomie excimers have been shown to occur mainly as the result of intermolecular reactions involving diatomic excimers as precursors. The three-body formation constants and quenching rates for collisional deexeitation of Xe2Cl, Xe2Br and Xe2F by rare gas, buffer gas and halogen donors and lifetime of triatomie excimer are reported.