Real time monitoring of the evaporative cooling: Application to the dynamics of NaI-(NH3)(n) clusters

The picosecond evaporation dynamics of ammonia molecules from Na(NH3)(n) cl usters produced via the dissociation of NaI within an ammonia cluster is st udied experimentally. A time dependence of the mass selected ion signal is observed only for one cluster size and not for larger clusters nor for smal ler ones. It will be shown that evaporation in the ionic state is responsib le for the absence of an observation of the evaporation in the neutral stat e. The variation of the ionization cross section with cluster size is the k ey point for the interpretation of the results. (C) 1999 American Institute of Physics. [S0021-9606(99)00603-0].