Vibrational relaxation and dephasing of Rb-2 attached to helium nanodroplets

The vibrational wave-packet dynamics of diatomic rubidium molecules (Rb-2) in triplet states formed on the surface of superfluid helium nanodroplets is investigated both experimentally and theoretically. Detailed comparison of experimental femtosecond pump-probe spectra with dissipative quantum dynamics simulations reveals that vibrational relaxation is the main source of dephasing. The rate constant for vibrational relaxation in the first excited triplet state 1(3)Sigma(+)(g) is found to be constant gamma approximate to E 0.5 ns(-1) for the lowest vibrational levels nu less than or similar to 15 and to increase sharply when exciting to higher energies.