Computational confirmation of C5N2 observed in rare-gas matrices

The structures and vibrations of several linear centrosymmetrical isomers of C5N2 were investigated by DFT. Triplet (3Σ−g) and open-shell singlet (1Σ−g) states of NCCCCCN were found to have the lowest energies. The calculated frequencies and isotope shifts are in excellent agreement with the experimental results of prominent vibrational bands observed in rare-gas matrices [Chem. Phys. 184 (1994) 233], thus confirming the conclusion that linear centrosymmetrical NCCCCCN was generated in rare-gas matrices. However, the calculated results are not in reasonable agreement with the observed frequencies of weaker bands, suggesting these weaker bands originate from something else.