Prediction of a new spin-forbidden transition in the N 2 molecule - C′′ 5 Π u  → B 3 Π g

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 309
• Main Authors: Minaev, Boris, da Silva, Ramon S., Panchenko, Olexander, Ågren, Hans
• Format: Journal Article
• Language: English
• Published: 2023
• Subjects: Metastable states; N2 spectrum; Quintet - triplet transitions; Spin-obit coupling
• ISSN: 1879-1352; 0022-4073
• DOI: 10.1016/j.jqsrt.2023.108701

A new spin-forbidden quintet-triplet C′′ 5 Π u  → B 3 Π g transition is predicted in the N 2 molecule on the ground of MRCI calculations with account of spin-obit coupling (SOC) by perturbation theory. The mechanism of its probability borrowing is quite similar to the recently calculated spin-forbidden electric dipole A′ 5 Σ g +  → A 3 Σ u + transition in the emission spectrum of the N 2 molecule. Neither of the two predicted emission systems have yet been observed in electric discharges but the calculated intensity provides a good chance for their detection. Both transitions, C′′–B and A′–A, borrow intensity from the First Positive System (B 3 Π g  → A 3 Σ u + ) and from the Herman Infrared Band (C′′ 5 Π u  → A′ 5 Σ g + ). The latter spin-allowed quintet-quintet transition provides strong depletion of the upper C′′ state; nevertheless, the energy pooling collisions of the triplet N 2 molecule and atomic recombination produce a permanent pumping of the C′′ 5 Π u states leaving a prominent emission with a detectable quantum yield. The proposed C′′ → B vibronic transitions have Einstein A coefficients in the order of 10 5 –10 4 s   − 1 , showing a considerable number of strong vibronic bands. As a consequence, the radiative lifetimes of the highest spin sublevel of the C′′ 5 Π u,1 irregular state are about 10 −6  s.