15min:

F. LACKNER, M. THEISEN, M. KOCH AND W. E. ERNST, Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria.

Cs atoms on the surface of helium nanodroplets have been excited to high lying nS (n = 8-11), nP (n = 8-11), and nD (n = 6-10) levels. A two-step excitation scheme via the 6²P_1/2(² _1/2) state using two cw lasers was applied. This intermediate state has the advantage that a large fraction of the excited Cs atoms does not desorb from the helium nanodroplets. An absorption spectrum was recorded by detecting laser induced fluorescence light from the 6²P_3/2 6²S_1/2 transition. The pseudo-diatomic model for helium nanodroplets doped with single alkali-metal atoms holds for the observed spectrum. An investigation of spectral trends shows that the n'²P( ) 6²P_1/2(² _1/2) and n'²D( ) 6²P_1/2(² _1/2) (n' > 9) transitions are lower in energy than the corresponding free-atom transitions. This indicates that the Cs*--He_\textrmriptsizeN potential becomes attractive for these highly excited states.
Our results suggest a possibility of generating an artificial super-atom with a positive ion core inside a helium nanodroplet and the electron outside, which will be subject to future experiments.

% S.~Fei, X.~Zheng, and M.~C.~Heaven, Chem.~Phys.~Lett. 176, 373