SiC₂ is a cyclic molecule with a fairly low barrier to linearity which is probably responsible for the large centrifugal distortion effects. Version 2 substantially revises versions 1 from Aug. 2007 and Jan. 2008. Initial starting parameters were derived from the main isotopolog by scaling with appropriate ratios of the lowest order parameters. The ²⁸SiC₂ parameters were taken from
(1) H. S. P. Müller, J. Cernicharo, M. Agúndez, L. Decin, P. Encrenaz, J. C. Pearson, D. Teyssier, and L. B. F. M. Waters, 2012, J. Mol. Spectrosc., 271, 50.
The J = 1 – 0 transition was measured in the laboratory by
(2) R. D. Suenram, F. J. Lovas, and K. Matsumura, 1989, Astrophys. J., 342, L103.
Additional laboratory data were reported by
(3) D. L. Kokkin, S. Brünken, K. H. Young, N. A. Patel, C. A. Gottlieb, P. Thaddeus, and M. C. McCarthy, 2011, Astrophys. J. Suppl. Ser., 196, Art. No. 17.
The set of parameters varied in the fit is quite similar to that in (3), albeit smaller by three. One line from (3) was omitted from the final fit because of a large residual. Predictions with uncertainties larger than 0.5 MHz should be viewed with caution.
The dipole moment was assumed to agree with that of the main isotopic species, see e052527.cat.