A new ⁴Σ − a⁴Π electronic transition of ScC in the near infra-red

A new ⁴Σ − a⁴Π_i electronic transition of ScC with (0,0)band near 12,700 cm⁻¹ has been discovered using laser-induced fluorescence, following the reaction of laser-ablated scandium metal with acetylene or methane under supersonic jet-cooled conditions. The new bands are weak, since the a⁴Π_i lower state is known from previous work to lie 160 cm⁻¹ above the X²Π ground state; several spectra needed to be co-added in order to improve the signal-to-noise ratio. The rotational structure of the new transition is dense and heavily blended, but analysis has been possible for the strongest sub-bands of the (1,0)and (2,0)bands, respectively at 13,301 and 13,899 cm⁻¹; extensive use was made of a band contour program for ⁴Σ − ⁴Π bands which listed the details of each line that it plotted. The bond length in the new ⁴Σ state is r₀ = 1.964 Å, which is 0.01 Å longer than in the ground state; its vibrational frequency is 607 cm⁻¹. There is no information in the spectrum giving the Kronig symmetry of the new state, though its electron configuration is probably (C 2pσ)¹ (C 2pπ)² (Sc 4sσ)¹ (Sc 3dδ)¹. Unexpectedly, the spin-spin interaction parameter, λ, in the new ⁴Σ state is negative, which suggests complicated interactions with nearby unseen electronic states.