The ground state fundamental rotational transition was published in
(1) M. Krüger, W. Stahl, and H. Dreizler, 1993, J. Mol. Spectrosc. 158, 298.
One additional lower J transition frequencies was taken from astronomical observations by
(2) J. Cernicharo, B. Tercero, C. Cabezas, M. Agúndez, E. Roueff, R. Fuentetaja, N. Marcelino, and P. de Vicente, 2024, Astron. Astrophys. 682, L13.
The initial J = 5 – 4 transition frequency published in (2) was deemed to be too high in frequency. A reanalysis by
(3) J. Cernicharo, 2024, private communication;
indicates the feature may be caused by two lines, of which the lower frequency value was employed in the present fit.
The D value was kept fixed to the value of the main isopolog scaled by the square of the ratio of the B values.
The calculation may be accurate enough throughout, but some caution is advised.
The experimental dipole moment of HCCNC was published by
(4) M. Krüger, H. Dreizler, D. Preugschat, and D. Lentz, 1991, Angew. Chem. 103, 1674.