The Radio Spectra of S[CLC]i[/CLC]CCH, S[CLC]i[/CLC]CN, and S[CLC]i[/CLC]NC

Abstract

Three new silicon-bearing radicals of astrophysical interest, SiCCH and the two nearly isoenergetic isomers SiCN and SiNC, were detected in a laboratory discharge in their ground states by Fourier transform 2 X P microwave and millimeter-wave absorption spectroscopy. Hyperfine structure was observed in the low rotational transitions of the 2 P 1/2 ladder, and well-resolved L-doubling was observed in both fine-structure ladders. With the spectroscopic constants derived from the laboratory measurements, the spectra of all three can be calculated to an uncertainty of less than 0.1 km s Ϫ1 in equivalent radial velocity over the entire range of interest to radio astronomers. SiCN, with a dipole moment of 2.9 D, is probably the most promising of the three for astronomical discovery.