@article{1538-4357-483-2-L135, author={M. J. Travers and M. C. McCarthy and C. A. Gottlieb and P. Thaddeus}, title={Laboratory Detection of the Ring-Chain Molecule C5H2}, journal={The Astrophysical Journal Letters}, volume={483}, number={2}, pages={L135}, url={http://stacks.iop.org/1538-4357/483/i=2/a=L135}, year={1997}, abstract={The highly polar ring-chain C 5 H 2 , a carbene with a singlet electronic ground state, has been detected with a Fourier transform molecular beam microwave spectrometer in the same diacetylene-neon discharge in which a carbene with the same elemental formula but a linear backbone was recently found. Thirteen a - and b -type rotational transitions between 6 and 27 GHz were measured to 1-2 kHz, and precise values of the three rotational constants and two centrifugal distortion constants were determined. With these, the entire microwave and millimeter-wave spectrum of C 5 H 2 can be calculated to an accuracy of 0.2 km s -1 or better. The identity of the new molecule as C 5 H 2 , which is fairly certain because of the close agreement between the measured rotational constants and those calculated ab initio, is conclusively confirmed by detection of the totally deuterated and two partially deuterated isotopic species at exactly the expected isotope shifts.} }