Reinvestigation of the Rb2 (2)3Πg-a 3Σu+ band on helium nanodroplets

It is well known that alkali-metal molecules are preferentially observed in the weak van der Waals-bound high spin states by helium droplet isolation spectroscopy. In [F. R. Bruhl et al., J. Chem. Phys. 115, 10275 (2001)] the Rb-2 (2)(3)Pi(g)-a (3)Sigma(+)(u) band on He droplets was investigated by laser-induced fluorescence and dispersed emission spectroscopy. At that time no information on the magnitude of spin-orbit coupling was available for the (2)(3)Pi(g) state which connects to the atomic 5s+4d asymptote and it was neglected. In this work we reinvestigate the observed spectra. The dispersed emission spectra, which resulted from free molecules, are consistent with state-of-the-art nonrelativistic potential energy surfaces and effective spin-orbit coupling matrix elements obtained from resonance-enhanced multiphoton ionization spectroscopy of cold Rb dimers [J. Lozeille et al., Eur. Phys. J. D 39, 261 (2006)]. Having validated the theoretical description of the free molecule state, we use the laser-induced fluorescence spectrum to discuss the influence of the He droplet on the excitation band. (c) 2010 American Institute of Physics. [doi:10.1063/1.3308493]