State to state collision energy transfer in singlet states of Li2

This Letter reports on state to state collision energy transfer in the A1Σu+ and G(2)1πg states of both 7Li2 and 6Li7Li dimers. The molecules were electronically excited by a single laser excitation or by using optical-optical double resonance (OODR) technique. Either a fluorescence or an ionization signal was monitored. A breakdown of the symmetric antisymmetric (s ⇎ a) rotational level selection rule was observed for collisional transitions in the A1Σu+ state of th nearly homonuclear 6Li7Li molecule. However, no s ⇎ a radiative transition breakdown was detected when we attempted the X1Σg+ → A1Σu+ → C(1)1πg ungerade-ungerade electronic excitation. Propensities for rotational energy transfer in the G(2)1πg state are discussed.