Triplet states of rubidium dimers on helium nanodroplets

Rubidium dimers in their 1 (3)Sigma (+)(u) states are formed through collisions of Rb atoms that have been deposited on the surface of helium nanodroplets. Visible absorption spectra between 550 and 690 nm were probed by laser induced fluorescence and emission spectra measured for selected excitation wavelengths. A system absorbing around 595 nm with its emission to the ground state centered at 604 nm is identified as the Rb-2 2 (3)Pi (g)-1 (3)Sigma (+)(u) transition. A broad unstructured band is measured near 667 nm. Following its excitation, two fluorescence channels are detected, one representing the 1 (1)Pi (u)-1 (1)Sigma (+)(g) (Rb-2 B-X) transition and the other leading to atomic Rb D-1 and D-2 emission. Various explanations of this observation are discussed, each of which requires the presence of a third rubidium atom on the droplet. All spectra have been modeled using energy potentials from previous theoretical work and the results are compared. Relaxation after laser excitation experiences various bottlenecks, which show up in the vibrational emission intensities and may be interpreted in terms of intramolecular interactions. (C) 2001 American Institute of Physics.