Collision induced fragmentation of small ionic alkali clusters. III. Heteronuclear clusters

Fragmentation of small heteronuclear NapKn-p+ clusters (n = 3-7, p = 0-2) i nduced by collision with helium atoms is investigated at a laboratory energ y of 4800 eV. Populations of the various fragmentation pathways are measure d. Detailed analysis of the collision is performed with a multicoincidence technique allowing the determination of the velocity vectors of the fragmen ts. Fragmentation is predominantly induced by momentum transferred in binar y collisions between He and alkali cores, electronic excitation accounting only for about 10% of the process. Experiments with heteronuclear clusters allow the study of the various fragmentation mechanisms following the initi al momentum transfer.Two-step fragmentation processes are governed by the e ndothermicity of the pathway while direct ejection of an alkali atom in bin ary collisions is directly dependent on the relative number of Na and K cor es. (C) 2001 American Institute of Physics.