Formation times of RbHe exciplexes on the surface of superfluid versus normal fluid helium nanodroplets -: art. no. 023402

Nanodroplets of either superfluid He-4 or normal fluid He-3 are doped with Rb atoms that are bound to the surface of the droplets. The formation of RbHe exciplexes upon 5P(3/2) excitation is monitored in real time by femtosecond pump-probe techniques. We find formation times of 8.5 and 11.6 ps for (RbHe)-He-4 and (RbHe)-He-3, respectively. A comparison to calculations based on a tunneling model introduced for these systems by Reho et al. [J. Chem. Phys. 113, 9694 (2000)] shows that the proposed mechanism cannot account for our findings. Apparently, a different relaxation dynamics of the superfluid opposed to the normal fluid surface is responsible for the observed formation times.