Formation and relaxation of RbHe exciplexes on He nanodroplets studied   by femtosecond pump and picosecond probe spectroscopy
  Vibrationally resolved photoionization spectra of RbHe exciplexes forming on He nanodroplets are recorded using femtosecond pump-probe spectroscopy with amplitude-shaped probe pulses. The time-evolution of the spectra reveals an exciplex formation time ~10ps followed by vibrational relaxation extending up to >1ns. This points to an indirect, time-delayed desorption process of RbHe off the He surface. 
C. Giese, T. Mullins, B. Gruener, M. Weidemueller, F. Stienkemeier,   and M. Mudrich
physics.atm-clus