Laboratory Detection of a Bent-Chain Carbene Isomer of C[TINF]6[/TINF]H[TINF]2[/TINF

Abstract

The rotational spectrum of a bent singlet isomer of the C6H2 carbene, a carbon chain that has been observed in the laboratory and in space, was detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. The three rotational constants and the leading centrifugal distortion constants were determined to high accuracy, allowing the entire rotational spectrum of this molecule below 120 GHz to be calculated to a fraction of 1 km s-1 in equivalent radio velocity. The spectroscopic constants agree well with those recently calculated from high-level ab initio methods by Sattelmeyer & Stanton. Although bent C6H2 is calculated to lie 54 kcal mol-1 above the ground-state isomer triacetylene, it is comparable in polarity and stability to the previously observed cumulene carbene with a linear carbon backbone. Rotational lines of bent C6H2 can be detected in the laboratory with a signal-to-noise ratio of better than 20 in 1 minute of integration, implying that several six-membered ring isomers of C6H2 lying about 40 kcal mol-1 above ground may also be found in the laboratory and in space.