SPECTROSCOPY AND DYNAMICS OF NEUTRAL ATOMS IN SUPERFLUID-HELIUM

Optical spectra and radiative lifetimes of neutral atoms in superfluid helium have been studied. The absorption and emission spectra of Ag, Mg, Yb, Al, Ga, and In were found to exhibit shifts and broadening typical of atoms residing in microscopic He bubbles, showing that this type of trapping is fairly general. The radiative lifetimes measured for these atoms are close to the free space values, indicating that the surrounding bubble hardly perturbs the electronic orbitals during photo emission. One exception observed in Sr is discussed, where competing autoionization substantially decreases the lifetime of a high excited triplet state. A transient non-bubble state with sharp, free atom like spectra is seen during the first few mu s after dispersion for many atomic species. The dynamics of this state are unusual, with for example very short radiative lifetimes measured for light alkali atoms.