Spectroscopy of barium attached to superfluid helium clusters

To complement the data on absorption spectra of alkaline earth atoms attach ed to superfluid helium clusters Ne are reporting on barium atoms attached to He-4(N). The absorption spectrum of the lowest singlet transition is blu e-shifted and strongly broadened compared to the corresponding unperturbed Ba (6s6p P-1(1)0 <-- 6s(2) S-1(0)) transition in accord with the observatio ns on Sr and Ca added to He-N [F. Stienkemeier, F. Meier, and H.O. Lutz: J. Chem. Phys. 101(24), 10816 (1997)]. Moreover, we compare the asymptotic va lues of shift and width of the excitation spectrum with increasing helium c luster size HeN ((N) over bar approximate to 1000 up to (N) over bar approx imate to 10 000) to those found for barium atoms in bulk liquid helium.