Two new isomers of the C5H2 molecule have been detected in the laboratory, and their microwave spectra
have been characterized to high accuracy. Both are good candidates for radio astronomical detection. Like the
two isomers previously detected in the laboratory, both are closed-shell carbenes, and both are extremely polar
and fairly stable. The first, calculated to lie 0.73 eV above isomer 1, the C5H2 ring-chain ground state, has a
bent carbon chain backbone with single, double, and triple bonds; the second, calculated to lie only 0.19 eV
higher in energy, is a new type of ring chain formed by adding a pair of doubly bonded carbon atoms to the
top of the C3H2 ring, which is one of the most abundant interstellar molecules.