Studies of the diffuse bands of K2, Rb2, and Cs2

Direct dye laser excitation of the K2 yellow (566-580-nm), Rb2 orange (590-610-nm) and Cs2 near-infrared (702-722-nm) diffuse bands has been investigated. Experimental results are consistent with 2 3 Π g (bound) ← 1 3 Σ u + (free) excitation followed by bound → free fluorescence. For Rb2 and Cs2, spin-orbit interactions become so significant that the 23Π g state is strongly split into three independent component states and this is observed in the spectra. We have investigated the free-bound-free fluorescence of the K2 yellow diffuse band in particular detail. Theoretical treatment and quantum-mechanical simulation of free-bound-free resonance fluorescence are described for comparison with our single longitudinal mode dye laser direct excitation experiments and measurements of the weak absorption in the same spectral region.