New pair of A1Σu+∼b3Πu mixed levels in 6Li7Li

A new pair of singlet–triplet A1Σu+∼b3Πu mixed levels of 6Li7Li has been identified and used here as window levels in pulsed perturbation-facilitated optical–optical double resonance (PFOODR) experiments to study the high-lying triplet 23Δg state. The new mixed levels reported here enhance access to the high-lying triplet states through the expansion of the Franck–Condon overlap factor range, at the same time allowing for more reliable determination of rotational constants. New molecular constants of the 23Δg state are reported here.