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The J = 1 – 0 transition
frequencies were reported by
(1) D. T. Halfen and L. M. Ziurys,
2004, Astrophys. J. 607, L63.
Also used in the fit were extensive infrared
measurements from
(2) J. L. Deutsch, W. S. Neil, and D. A. Ramsay,
1987, J. Mol. Spectrosc. 125, 115;
and from
(3) F. Ito, T. Nakanaga, H. Takeo, and H. Jones,
1994, J. Mol. Spectrosc. 164, 379.
The predictions should be quite reliable throughout
because of the extensive IR data used in the fit.
The 27Al hyperfine splitting has been resolved
in the laboratory, but it probably does not matter for
astronomical observations.
Nevertheless, a separate prediction considering
27Al hyperfine splitting with J" ≤ 4
is available. 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 !
Vibrational contributions have been considered in
the calculation of the partition function. Values for
the ground state are given in parentheses.
Note:
D. T. Halfen and L. M. Ziurys,
2014, Astrophys. J. 791, Ar. No. 65
report an overlap of the two strongest HFS components
of the J = 2 – 1 around
755.200 GHz, about 10 MHz too low. Not only
are the transition frequencies incompatible with the
infrared data of AlH, the resulting distortion parameter
D is incompatible with infrared data of AlD or
with rotational data of AlD by Halfen and Ziurys even
under consideration of the breakdown of the Born-Oppenheimer
approximation.
The ground state dipole moment has been taken from an
ab initio calculation by
(4) W. Meyer and P. Rosmus,
1975, J. Chem. Phys. 63, 2356.
The predictions should be reliable up to about
1.0 THz.
Note: The dipole
moment of aluminum monohydride shows very pronounced
vibrational effects. Moreover, its calculated value
depends very strongly on the degree of electron
correlation. A different article by
(5) J. M. O. Matos, B. O. Roos, A. J. Sadlej,
and G. H. F. Diercksen,
1988, Chem. Phys. 119, 71,
quote as ground state value calculated at their
highest level 0.300 D. Therefore, intensity
predictions should be viewed with great care.
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