Molecular beam study of surface chemi-ionisation

Abstract

Surface chemi-ionisation has been observed when a supersonic rubidium nozzle beam impinges on a frozen iodine layer at ∼100 K. Only a small fraction < 10^–5 of reactive collisions at the surface give rise to chemi-ionisation. Similar quantities of positive and negative ions are formed but application of a magnetic field shows that electrons are not emitted. The time dependence of the chemi-ionisation signal on a thick iodine layer shows evidence of surface charging and the onset of charge conduction through the layer. The form of the chemi-ionisation signal as a function of surface potential shows evidence of surface polarisation. The experimental results are discussed in terms of an electron jump model of the surface reaction dynamics.