LABORATORY DETECTION OF THE RING-CHAIN MOLECULE C_7H_2

摘要

Following the recent laboratory detection of the ring-chain carbene C_5H_2, we have now detected C_7H_2, the next longer member of the sequence formed by substituting a carbon chain for one of the hydrogen atoms of cyclic C_3H_2. The strongest lines, again obtained with a diacetylene-neon discharge, were roughly 15 times weaker than those of C_5H_2. Enough rotational lines were detected in both the normal and doubly deuterated isotopic species to be certain of the identification and to obtain the rotational and leading centrifugal distortion constants accurately enough for calculation of the entire rotational spectrum below 300 GHz to a fraction of 1 km s~(-1) in equivalent radial velocity. The ring chain here is calculated to be the most stable isomer of C_7H_2 and extremely polar, so it is of considerable astronomical interest. Several other isomers of C_7H_2 may be detectable in the laboratory and in space with present techniques.