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Gottlieb, C.A., E.W. Gottlieb, and P. Thaddeus, 1983: Laboratory and astronomical measurement of the millimeter wave spectrum of the ethynyl radical CCH. Astrophys. J., 264, 740-745, doi:10.1086/160647.
The N = 0 → 1 and 1 → 2 rotational transitions of CCH at 87 and 174 GHz, respectively, have been detected in a laboratory glow discharge in a mixture of He and C2H2. The spectroscopic constants of CCH derived from measurements of the hfs of the transitions agree well with those derived from astronomical observations, confirming the astronomical detection of CCH (Tucker, Kutner, and Thaddeus). As the CCH lines in the Orion Nebula are narrower than the laboratory lines but less certain in rest frequency owing to uncertainty in the radial velocity, the most accurate values for the spectroscopic constants of CCH are obtained from a simultaneous fit of both the laboratory and astronomical data: for the rotation, centrifugal distortion, spin-rotation, and hyperfine constants, respectively, we find B0 = 43674.534±0.006 MHz, D0 = 0.1071±0.0008 MHz, γ = -62.606±0.004 MHz, b = 40.426±0.019 MHz, and c = 12.254±0.026 MHz.
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