The molecule may be the lowest energy isomer of SiC₃. With respect to the first entry from Jan. 2000, the majority of the experimental transition frequencies were taken from
(1) M. C. McCarthy, C. A. Gottlieb, and J. Cernicharo, 2019, J. Mol. Spectrosc. 356, 7.
As in the case of the initial entry, data were also taken from
(2) A. J. Apponi, M. C. McCarthy, C. A. Gottlieb, and P. Thaddeus, 1999, J. Chem. Phys. 111, 3911;
and from
(3) M. C. McCarthy, A. J. Apponi, and P. Thaddeus, 1999, J. Chem. Phys. 110, 10645;
Whereas in (1) only one transition frequency from (2) was used, we used almost all transitions of (1) and (2), employing uncertainties of 20 kHz, as in (1). Uncertainties of FTMW data in (1) were set to 1 kHz, as in (3). Only a small number of transitions of (1) and (2), which exhibited larger deviations between measured and calculated frequencies, were omitted. The current fit has one parameter less than that of (1), and two less than that of (2).
The entry should be sufficient for all astronomical observations. Transition frequencies with calculated uncertainties of more than 0.2 MHz should be viewed with caution.
The dipole moment is from an ab initio calculation by
(4) H. S. P. Müller and D. E. Woon, 2013, J. Phys. Chem. A 117, 13868.