C₅N₂ revisited: Mass-selective matrix isolation and DFT studies

Experiments employing mass-selected ion deposition in neon matrices confirm that a spectrum with origin near 440 nm, which we have previously reported, indeed corresponds to the C₅N₂ mass, as tentatively assigned. The spectrum consistently appears when mass 88 is deposited, but is absent when other C_mN_n species are selected. We discuss the observed spectra in light of the recently reported theoretical density functional calculations, as well as new calculations which we have carried out. Taking into consideration computed band frequencies, observed isotopic shifts, and spectroscopic selection rules, consistent assignments for all the nine observed vibrational frequencies of the carrier can be proposed.