The 846 nm A′ 3Σ−u←X 3Σ−g band system of jet-cooled V2

The 846 nm band system of jet-cooled 51V2 has been recorded using resonant two-photon ionization spectroscopy, and is assigned as the A′ 3Σ−u←X 3Σ−g band system. Both the Ω′=1u←Ω″=1g and Ω′=0+u←Ω″=0+g subbands of the 0–0 band have been rotationally resolved and analyzed. Although the transition could, in principle, correspond to a π*g←πu or σ*u←σg excitation, it is assigned as a δ*u←δg excitation. Either of the other two possibilities makes it difficult to rationalize the small reduction in bond length which accompanies the excitation [re(X 3Σ−g)=1.77 Å, r0(A′ 3Σ−u)=1.756 Å]. In addition, the second order spin–orbit splitting of the ground X 3Σ−g state is reanalyzed to predict the existence of a 1Σ+g state, arising from the same sσ2gdσ2gdπ4udδ2g electronic configuration as the X 3Σ−g ground state, at an energy about 1821 cm−1 above the ground state. This allows a state previously observed in an electronic resonance Raman effect 1860 cm−1 above the ground state to be positively identified as the sσ2gdσ2gdπ4udδ2g, 1Σ+g state, which is responsible for the anomalous spin–orbit splitting in the ground X 3Σ−g state. A similar analysis of the spin–orbit splitting of the A′ 3Σ−u state predicts the location of the sσ2gdσ2gdπ4u dδ1gdδ*1u, 1Σ+u state at 13 426 cm−1 above the V2 X 3Σ−g(0+g) ground state.