Investigating the Double Resonance Spectrum and Lifetime Measurements of the Excited 4¹Σ_g⁺ State of Lithium Dimers

We report a double-resonance laser spectroscopy study of the lithium dimers and radiative lifetime measurements of the 4¹Σ_g⁺(10,23) state. Two tunable pulsed dye lasers selectively excite Li₂ molecules from thermally populated levels in the X¹Σ_g⁺ ground state to the final 4¹Σ_g⁺(10,23) state through the intermediate A¹Σ_u⁺ (4,22) state. The molecular decay fluorescence from the final state was collected using a high-resolution imaging spectrometer. The rovibrational structures of the spectrum were analyzed and compared with the computed Franck–Condon factors. Spectroscopic constants of the ground electronic state were determined using the Birge–Sponer method. Excited-state lifetimes were measured using time-correlated photon-counting technique, and the collisionless lifetime was obtained from a Stern–Volmer analysis. We compare experimental results with the theoretical lifetime calculations, done by the Seth Ashman Group at Providence College.