Please note that this entry deals with the symmetric isotopomer with one ¹³C. The transition frequencies were largely taken from
(1) M. Bogey, C. Demuynck, J. L. Destombes, and H. Dubus, 1987, J. Mol. Spectrosc. 122, 313.
Additional lines were published by
(2) S. Spezzano, F. Tamassia, S. Thorwirth, P. Thaddeus, C. A. Gottlieb, and M. C. McCarthy, 2012, Astrophys. J. Suppl. Ser. 200, Art. No. 1.
The uncertainties in (1) are overall somewhat conservative. Nevertheless, one line with large residuals in recent fits has been omitted from the final fit. Some higher order parameters were taken from the main spcies and were kept fixed after scaling.
Predictions with uncertainties larger than 0.5 MHz should be viewed with caution.
The ¹³C hyperfine splitting has been resolved to a large degree in (2). The hyperfine splitting may be be resolvable in astronomical observations of cold sources. Therefore, a separate hyperfine calculation is provided up to J = 2 and up to 150 GHz. The partition function values include the spin-multiplicity of the ¹³C nucleus.
At lower temperatures, it may be useful to distinguish between ortho-c-C₃H₂ and para-c-C₃H₂. The ortho and para levels are described by K_a + K_c = odd and even, respectively, with a spin-weight ratio of 3 : 1. The J_KaKc = 1₀₁ level is the lowest ortho state. However, it is only 1.619243 cm^–1 above ground.
Separate para and ortho predictions are available up to about 200 GHz along with separate para and ortho partition function values. Note: the spin-weight of 3 for the separate ortho predictions has not been eliminated. Please note also that there are matrix-elements which mix ortho and para levels. However, these matrix-elements are small. Nevertheless, larger effects may occur in cases of accidental near-degeneracies of certain levels.
The dipole moment was assumed to agree with that of the main species, see e038506.cat.