A new search for interstellar C3

A new, very sensitive search for interstellar triatomic carbon has resulted in upper limits for a few diffuse clouds of order 10 to the 10th/sq cm, or about 10 to the -11th with respect to hydrogen. These limits are consistent with recent cold diffuse cloud chemistry models, but may be in conflict with shocked cloud models such as those invoked to explain CH(+) abundances. The results mmay also argue against linear carbon-chain molecules as carriers of the diffuse interstellar bands. 30 references.