Characterisation of the b³Σ⁺ state and its interaction with the A¹Π state in aluminium monofluoride

Recently, we determined the detailed energy level structure of the X1Σ+, A1Π and a3Π states of AlF that are relevant to laser cooling and trapping experiments [Truppe et al., Phys. Rev. A. 100 (5), 052513 (2019)]. Here, we investigate the b3Σ+,v=0 state of the AlF molecule. A rotationally resolved (1 + 2)-REMPI spectrum of the b3Σ+,v′=0 ← a3Π, v′′=0 band is presented and the lifetime of the b3Σ+,v=0 state is measured to be 190(2) ns. Hyperfine-resolved, laser-induced fluorescence spectra of the b3Σ+,v′=0 ← X1Σ+, v′′ = 1 and the b3Σ+,v ′ = 0 ← a3Π, v′′ = 0 bands are recorded to determine fine- and hyperfine structure parameters. The interaction between the b3Σ+,v = 0 and the nearby A1Π state is studied and the magnitude of the spin–orbit coupling between the two electronic states is derived using three independent methods to give a consistent value of 10(1) cm-1. The triplet character of the A state causes an A → a loss from the main A−X laser cooling cycle below the 10-6 level