Fourier transform emission spectroscopy and ab initio calculations on the visible spectrum of AlD[formula omitted

Abstract

The spectrum of the AlD+ isotopologue has been investigated at high resolution in the 27,000−29,000 cm−1 region using a Fourier transform emission spectroscopy technique. The AlD+ molecules were produced within a water-cooled aluminum hollow-cathode lamp in the presence of 1.5 Torr of Ne and 0.8 Torr of ND3. The (0, 0) and (1, 1) bands belonging to the A2Π−X2Σ+system were recorded with an instrumental resolution of 0.03 cm−1. In total, almost 500 rotational frequencies were measured with an absolute accuracy of about 0.005 cm−1. It improved the experimental accuracy of the determined frequencies by the factor 10 compared to the previous work [J Phys B: Mol Phys 1984;17:L861-L866]. The rotational analysis has shown irregularities in the Λ− doubling splitting of the A2Π v=0,1. Consequently, the A2Π state has been represented by the rotational term values, while the regular X2Σ+ state by the molecular constants. The causes of the irregularities were identified in the interaction between the A2Π and the B2Σ+ states, which lies about 3720 cm−1 above. Supporting ab initio quantum chemical calculations, including spin-orbit effects, reproduce the observed spectroscopic constants including the small energy splittings due to spin-rotation interactions (for 2Σ+ states) and Λ−doubling.