Molecular dynamics simulation of metal cluster cooling and heating in noble gas atmosphere

Metal cluster properties such as ionization potential and reactivity strongly depend on the temperature of the cluster. Using molecular dynamics simulation we have investigated how much energy is transferred from noble gas atoms to unsupported Pd-13 clusters in collisions. Furthermore we propose a two-term density of states for Pd-13 which leads to excellent prediction of the caloric equation of state obtained in simulations. Knowing the heat capacity of the cluster, the energy transfer can be converted into change of cluster temperature per collision at constant gas temperature and the cooling and heating of the cluster can be predicted. The predictions were in good agreement with cooling and heating simulations. Approximately 2000 collisions are required to cool Pd-13 from 1500 K to 100 K in a helium gas at 100 K. (C) 1999 Acta Metallurgica Inc.