Isomers of cyanodiacetylene: Theoretical structures and IR spectra

An extensive DFT study on possible HC5N isomers yielded seven lowest energy species, of direct interest to the photochemistry of cyanodiacetylene, an astrophysically-relevant molecule. Coupled-clusters CCSD(T) geometries and relative energies are given for these isomers together with B3LYP-predicted IR spectra. Attention is drawn to the importance of branched structures.