JOHANN V. POTOTSCHNIG, MARTIN RATSCHEK, ANDREAS W. HAUSER AND WOLFGANG E. ERNST, Institute of Experimental Physics, TU Graz, Petersgasse 16, 8010 Graz, Austria.
Chromium (Cr) atoms embedded in superfluid helium nanodroplets (HeN) have been investigated by laser induced fluorescence, beam depletion and resonant two-photon ionization spectroscopy in current experiments at our institute. Cr is found to reside inside the HeN in the a7S ground state. Two electronically excited states, z7P and y7P, are involved in a photoinduced ejection process which allowed us to study Fano resonances in the photoionisation spectra. The need for a better understanding of the experimental observations triggered a theoretical approach towards the computation of electronically excited states via high-level methods of computational chemistry. Two well-established, wave function-based methods, CASSCF and MRCI, are combined to calculate the potential energy curves for the three states involved. The character of the two excited states z7P and y7P turns out to be significantly different. Theory predicts the ejection of the Cr atom in the case of an y7P excitation as was observed experimentally. The quasi-inert helium environment is expected to weaken spin selection rules, allowing a coupling between different spin states especially during the ejection process. We therefore extend our theoretical analysis to the lowest state in the triplet- and quintet- manifold. Most of these alternative states show very weak bonding of only a few cm-1.