The transition frequencies have been reported by
(1) M. Sun, D. T. Halfen, J. Min, D. J. Clouthier, and L. M. Ziurys, 2012, Chem. Phys. Lett. 553, 11.
The lowest two transitions were also reported by
(2) C. Cabezas, S. Mata, A. M. Daly, A. Martín, J. L. Alonso, and J. Cernicharo 2012, J. Mol. Spectrosc. 278, 31.
The sextic distortion parameter H was not determined in (1), as its uncertainty was not much smaller than the value. Nevertheless, its value appears to be fairly reasonable, and it was retained here. As a consequence, predictions are probably reliable only up to about 400 GHz or slighly higher.
A separate prediction with ²⁷Al hyperfine splitting is available for J' ≤ 12. Note: The partition function does not include the spin-multiplicities of ²⁷Al ! Therefore, partition function values have to be multiplied by 6 when considering ²⁷Al hyperfine splitting !
The dipole moment from an ab initio calculation was mentioned in (2).