Rotational detection of the silicon-carbon chains H2C3Si and HSiCCH

The rotational spectra of two new silicon -bearing carbon chains, H2C3Si and HSiCCH have been detected by means of Fourier -transform microwave spectroscopy in a supersonic jet source equipped with an electrical discharge. On the basis of measurements between 10 and 42 GHz, precise spectroscopic constants have been determined for both molecules. Along with H29SiCCH and H30SiCCH, which were detected in natural abundance, several other rare isotopic species of HSiCCH were observed using samples enriched in carbon -13 and D. From this isotopic data, a precise semi -experimental equilibrium structure was derived and compared with a re-evaluated semi -experimental equilibrium structure of the parent silylene SiH2; the deuterium isotopic measurements also provide important clues as to the formation pathway of HSiCCH in our discharge. Because other small Si -bearing chains have been detected in the circumstellar envelope of the evolved carbon star IRC+10216, both chains may be of astronomical interest.