Coherent multichannel nonadiabatic dynamics and parallel excitation pathways in the blue-violet absorption band of Rb2

The blue-violet absorption band in the Rb2 molecule at 430 nm is studied by ultrafast pump–probe spectroscopy and quantum dynamical calculations. We find that two electronic states are excited simultaneously and thereby the dynamics essentially proceeds in two independent channels. One channel exhibits vibrational motion in the D′(3)1Σ+u shelf state while the other involves the D(3)1Πu state which is heavily perturbed by spin–orbit interactions. Moreover, we directly observe the build-up of the wavefunction in the (4)3Σ+u state which together with (1)3Δu are proposed to be the major perturbers.