A new look at N[formula omitted] electronic transitions: An experimental and theoretical study

Abstract

Neutral and ionic N2 species exhibit a rich spectrum as a result of the large density of couplings between states with different multiplicities. In this sense, spectra of the molecular ion N2+ are investigated combining Fourier transform spectroscopy and ab initio methods. We have reanalyzed the First Negative band System (B2Σu+→ X2Σg+) including five bands not reported previously by Fourier spectroscopy. The spectra were recorded using a resolution of 0.6 cm−1 and accuracy of 0.005 cm−1. These results are then compared with new MRCI+Q/AV6Z calculations. For the first time, transition probabilities are computed for the previously observed 22Πg-A2Πu band system. The 22Πg state (Te = 67,029 cm−1) has a dissociation energy of 24,787 cm−1 at Re = 2.7332 a0. The predicted lifetimes for the 22Πg-A2Πu emissions are of the order of 170 ns. The calculated transition probabilities A(v′=0, v′′=0) for the B2Σu+-X2Σg+ and 22Πg-A2Πu bands are 1.156 × 107 and 1.716 × 103 s−1, respectively. The role of spin–orbit (SO) matrix elements in the spectroscopic data of N2+ is discussed, including results for SO constants as a function of vibrational level of A2Πu state. Our theoretical SO constant A0(A2Πu) = −73.40 cm−1 reproduces well the experimental one (−74.67 cm−1). SO calculations are also used to investigate spin-forbidden transitions on N2+. The obtained <A2Πu|HˆSO|a4Σu+>≈ 30 cm−1. Following a sum-over-states (SOS) methodology, the best estimate for the spin-rotation constant γ0 of the X2Σg+ and B2Σu+ states are 0.0096 and 0.0211 cm−1, respectively, in quantitative agreement with the present experimental data of 0.00917(36) and 0.0206(9).