AlCN is energetically higher than AlNC (e053501.cat) which has been detected already. The observed lines are from
(1) K. A. Walker and M. C. L. Gerry 1999, Chem. Phys. Lett. 301, 200.
The dipole moment is from an ab initio calculation by
(2) B. Ma, Y. Yamaguchi, and H. F. Schaefer, III 1995, Mol. Phys. 86, 1131.
According to (2), AlCN is higher in energy than AlNC by about 2000 cm^–1 or less.
It is conceivable that AlCN is, like its isomer AlNC, a rather floppy molecule. Because of this and because of the small number of rotational transitions studied so far, predictions of higher J transitions should be viewed with great caution !
Since the number of strong hyperfine components is 18 for each rotational transition with large J and since the splitting is < 1 MHz for J = 6 – 5 (at 71813 MHz) and higher, predictions are given without hyperfine splitting. For low J transitions, predictions with hyperfine splitting are also available. NOTE: the partition function takes into account hyperfine splitting in all instances !