Spectroscopy studies of the B1Πu state of Cs2

More than 1000 rovibrational transitions between the first excited B¹Π_u state and the ground XΣ_g⁺ state of Cs₂ were observed and analyzed. The laser-induced fluorescence of Cs₂ molecules pumping with a solid-state-pumped single-mode Ti:sapphire laser was detected with an ultra-high resolution monochromator and photo-multiplied tube. The high level density and small electronic separation of cesium dimers due primarily to the large dipolar interactions and heavy nuclei comparing with the lighter alkalis make the laser-induced fluorescence unresolvable. The ultra-high resolution monochromator acts as a band path filter (about 1 cm^-1 line width) and tuned to the favor transition to eliminate the other transitions. From the measured term values, Dumham coefficients, RKR potential of B¹Π_u state have been calculated which yield the potential parameters T_e=13043.638(5) cm^-1, R_e=4.85 Å, D_e=2338.5(8) cm^-1, B_e=0.01077(1) cm^-1, and ω_e=34.37(4) cm^-1. This is in good agreement with Diemer´s results.