Crossed Molecular Beam Study of Collision-induced Dissociation of Alkali Halides*

Recent studies by Berry et al. [1,2] of collisional dissociation of alkali halides by shockheated argon have shown that, in vibrationallyequilibrated gases, some alkali halides (all cesium, rubidium and potassium salts except RbI and KI) dissociate completely to ion pairs, although dissociation to neutral atoms requires less energy. An e_xpression for the branching ratio for the different dissociation products (atomic or ionic) has been postulated for these systems. The present experiments utilize the crossed molecular beam method for further investigation of the more elementary process of dissociation of CsI, CsBr and RbI to ion pairs by single collisions with high energy xenon atoms **+ . Since both the relative kinetic energy and internal energy of the reactants can be precisely controlled in a crossed molecular beam experiment, the dependence of the dissociation cross section on relative kinetic energy and alkali halide internal energy has been measured for collision energies up to 6 eV and alkali halide temperatures ranging from 1150oK to 16500K. Crude energy analysis oi the ions produced by these single collisions also reveals interesting dynamical features of collision-induced dissociation. The schematics of the experimental arrangement are shown in fig. la. Fast Xe is produced