15min:

JOHANN NAGL, ANDREAS W. HAUSER, GERALD AUBÖCK, OLIVIER ALLARD, CARLO CALLEGARI AND WOLFGANG E. ERNST, Institute of Experimental Physics, TU Graz, Petersgasse 16, 8010 Graz, Austria/EU.

We use helium droplets to assemble all possible combinations of trimers of potassium and rubidium (K₃, K₂Rb, KRb₂, Rb₃) in a quartet-spin state, and we measure their electronic excitation spectra in the range 10600--17400~cm^-1. We use two methods to separate overlapping spectra: visible-visible V-type double-resonance and mass-selective beam depletion. We observe and assign the laser-induced-fluorescence spectra of ten new bands. Assignment is backed by high-level ab initio calculations of the electronic levels structure of these molecules. Both experiment and calculations show highly regular patterns which we elucidate in terms of an electron-shell structure similar in spirit to that observed in Na clusters.