THE DEVELOPMENT OF THE 3P AND 4P VALENCE-BAND OF SMALL ALUMINUM AND GALLIUM CLUSTERS

Photoelectron spectra of Al-n(-) and Ga-n(-) clusters in the size rang e n=1-15 are presented. Using 5.0 and 3.68 eV W light (KrF excimer and nitrogen laser, respectively), electrons from molecular orbitals corr esponding td the 3p and 4p orbitals of the atoms are detached. The spe ctra reveal a rich fine structure not observed in earlier experiments. The data are compared with the results of quantum chemical calculatio ns. A change in the pattern of the spectra near n=6 can be interpreted as a transition from planar to compact 3D structures. The spectrum of Al-13(-) agrees with the icosahedral structure predicted for this par ticle. The data do not agree with jellium model predictions. Differenc es between Al and Ga data can be correlated with the larger binding en ergy of the Ga 4s band.