Data of several vibrational states and isotopologs were fit together. Ground state rotational transition frequencies of the main isotopic species were reported by
(1) T. Törring and R. Herrmann, 1989, Mol. Phys. 68, 1379;
and by
(2) C. Yamada, E. A. Cohen, M. Fujitake, and E. Hirota, 1990, J. Chem. Phys. 92, 2146.
Data within the first two excited vibrational states were taken from
(3) M. Goto, S. Takano, S. Yamamoto, H. Ito, and S. Saito, 1994, Chem. Phys. Lett. 227, 287.
Ground state data of the ¹⁸O isotopolog were taken from
(4) A. A. Breier, B. Waßmuth, T. Büchling, G. W. Fuchs, J. Gauss, and T. F. Giesen, 2018, J. Mol. Spectrosc. 350, 43.
A small number of lines with large residuals were omitted. The spectroscopic parameters differ somewhat from earlier published values, including the combined fit in (4). The calculations are straight extrapolations from the data pertaining to the first three vibrational state. The main concern should be the electron-spin splitting. Data for v = 3 may be quite good, increased caution is advised for higher v. Additional caution is advised above 720 GHz or for HFS components with calculated uncertainties larger than 0.2 MHz. ²⁷Al hyperfine splitting may be resolvable, in particular at low J. Therefore, a separate hyperfine calculation is provided for frequencies below 500 GHz. Please note that a sequential coupling scheme was employed.
The first 30 vibrational states were included in the calculation of partition function values. The spin multiplicity of 6 for ²⁷Al was considered in the entry without HFS splitting.
The dipole moment from a quantum-chemical calculation was reported by
(5) A. T. Patrascu, S. N. Yurchenko, and J. Tennyson, 2015, Mon. Not. R. Astron. Soc. 449, 3613.