2010ApJ...713..520H

The J = 2 ⟵ 1 and 3 ⟵ 2 rotational transitions of AlD (X ¹Σ⁺) near 393 and 590 GHz have been measured using submillimeter direct absorption spectroscopy. AlD was created in an AC discharge of Al(CH₃)₃ and D₂ in the presence of argon. This work is the first direct measurement of the J = 3 ⟵ 2 transition of AlD. Each transition was found to be split into multiple hyperfine components due to the ²⁷Al nuclear spin of I = 5/2, some of which are blended together. The data for AlD were fit with an effective Hamiltonian and rotational, electric quadrupole, and nuclear spin-rotation constants were determined for the molecule. The accuracy of these constants has been improved by a factor of 2-3, compared to previous studies. From these data, predictions for the J = 1 -> 0 and 4 -> 3 transitions of AlD have also been made. Photospheric AlH has been observed via its A ¹Π-X ¹Σ⁺ electronic transition, suggesting that this species may be present in circumstellar gas surrounding late-type stars, where four aluminum-bearing molecules have already been detected. High deuterium enrichment has been observed in hydride species in molecular clouds, making AlD a feasible candidate for searches in these objects as well.