CORE EXCITATION IN FREE CLUSTERS - IONIZATION, RELAXATION, AND FRAGMENTATION

Cluster-size-dependent spectroscopic changes are reported for the Ar(2 p) core ionization, electronic relaxation via Auger decay, and subsequ ent fragmentation of free argon clusters with sizes up to 700 atoms. E xcitation spectra recorded using zero kinetic energy (ZEKE) photoelect rons, Auger electrons, as well as multicoincidence ion mass spectra, a re reported. It is found that core ionization energies decrease as the cluster size increases from the atom to the condensed phase. Evidence for thermalization of photoelectrons via intracluster scattering is f ound, indicating that ZEKE photoelectrons are sensitive to the bulk of clusters. In contrast, Auger electron yield spectra are more sensitiv e to the surface of the clusters. Ion pair and triplet signals from di ssociative double and triple ionization are used to investigate the fi nal stabilization step of core-excited clusters. Fragmentation mechani sms are deduced for different cluster sizes.