High-resolution laser spectroscopy of the Swan system (d3Πg-a3Πu) of C2 in an organic halide-alkali metal flame

The 0–1 band of the Swan system (d³Π_g-a³Π_u) of C₂ has been recorded by laser-induced fluorescence of C₂ formed by reaction between Na and C₂Cl₄. Most of the spectrum was recorded at Doppler-limited resolution, but overlapped lines were resolved using sub-Doppler techniques. The Q branches of the $\text{ΔΩ = 0}$ subbands and rotational lines for which $\text{ΔΩ = ±1}$ are observed for the first time. Molecular parameters defined in the effective Hamiltonian of Brown and Merer are obtained for both ³Π states.