Theoretical studies of AlF, AlCl, and AlBr

Abstract

Accurate spectroscopic constants are presented for the lowest six singlet and lowest five triplet states of AlF and AlCl. We propose that the correct ordering of the triplet manifold in both molecules should be a ³Π, b ³Σ⁺, c ³Σ⁺, d ³Π, and e ³Δ. This supports the assignment of the triplet state observed at T_e=63 203 cm⁻¹ to a ³Δ state but changes the designation from d to e. Radiative lifetimes are computed for the excited states. In addition, we present a more detailed study of the A ¹Π–X ¹Σ⁺ transition in AlF, AlCl, and AlBr. For AlF and AlCl, potential curves for the X ¹Σ⁺ and A ¹Π states, and A–X transition moment functions, are presented, together with Einstein coefficients and A ¹Π vibrational lifetimes. The respective lifetimes for the v=0 level of the A ¹Π states are observed to increase from about 1.9 ns for AlF to 5.2 ns for AlCl to about 8.5 ns for AlBr. The value for AlCl agrees with a recent laser‐induced fluorescence study to within the experimental error bars.