Spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets

The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb-2) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb-2 molecules off the droplets and due to their low internal temperature, wave-packet oscillations can be followed up to very long pump-probe delay times greater than or similar to 1.5 ns. In the first-excited triplet state (1)(3)Sigma(+)(g), full and fractional revivals are observed with high contrast. Fourier analysis provides high-resolution vibrational spectra which are in excellent agreement with ab initio calculations.