Homo- and heteronuclear alkali metal trimers formed on helium   nanodroplets. II. Femtosecond spectroscopy and spectra assignments
  Homo- and heteronuclear alkali quartet trimers of the type K_{3-n}Rb_{n} (n=0,1,2,3) formed on helium nanodroplets are probed by one-color femtosecond photoionization spectroscopy. The obtained requencies are assigned to vibrations in different electronic states by comparison to high level ab initio calculations of the involved potentials including pronounced Jahn-Teller and spin-orbit couplings. Despite the fact that the resulting complex vibronic structure of the heavy alkali molecules complicates the comparison of experiment and theory we find good agreement for many of the observed lines for all species. 
Christian Giese, Frank Stienkemeier, Marcel Mudrich, Andreas W. Hauser   and Wolfgang E. Ernst
physics.atm-clus