Knowledge Bank

When a very dilute mixture of NCCN in neon is codeposited at 4.3 K with a beam of neon atoms that have been excited in a microwave discharge, prominent infrared absorptions of the uncharged isomers CNCN and CNNC appear in the resulting solid. The $\nu 3$ absorption of NCCN$+$ is also very prominent, and the ground-state $\nu 1$ + $\nu 3$ absorption of that product is observed for the first time. Photoisomerization to CNCN$+$, for which the two CN-stretching fundamentals are identified, occurs in the red spectral region, and photodestruction of both NCCN$+$ and CNCN$+$ occurs in the near ultraviolet. The photochemistry of these two cations is correlated with recently published results of experimental and quantum chemical studies of their electronic energy levels.