Ionization potential of Al-6 and Al-7 as a function of temperature

The temperature-depence of the ionization potential of Al-6 and Al-7 cluste rs is studied by using ab initio molecular dynamics. The threshold regions of theoretical photoionization efficiency curves are obtained from the calc ulated ionization potential distributions by integration and the determined ionization potentials are compared with the experimental ones. Two importa nt effects, which complicate the determination of ionization potential from photoionization efficiency curves, are observed: the thermal tail effect a nd the isomerization. Also a link between the adiabatic ionization potentia l and the threshold of the photoionization efficiency curve is discussed. I n the case of Al?, this often used connection breaks down.