The [20.4]3Φ→(1)3Δ Green System of LaF

Abstract Electronic bands belonging to the [20.4] 3 Φ→(1) 3 Δ system have been observed in the emission spectrum of lanthanum monofluoride at high temperature in the presence of the Ar + 457.9-nm laser line: the (0–0), (1–1), (2–2), and (3–3) bands of the 3 Φ 4 → 3 Δ 3 subsystem and the (0–0) bands of the 3 Φ 3 → 3 Δ 2 and 3 Φ 2 → 3 Δ 1 subsystems. Rotational structures which are well developed in these experimental conditions were analyzed. The data were treated using a polynomial expression for the upper levels term-values, directly at equilibrium for 3 Φ 4 , whereas a previous Hamiltonian matrix representation of the (1) 3 Δ state was assumed. A Hund's case (a) representation of the [20.4] 3 Φ state at v =0 was also considered. Perturbations affecting 3 Φ 2 levels at v =0 were observed; the energy and rotational constant of the perturbing state and the interaction parameter were estimated.