The singlet–triplet splittings of NCN

The photoelectron spectrum of the cyanonitrene anion, NCN−, has been measured at 416 and 266 nm. The 266 nm spectrum reveals the ã 1Δg and the b̃ 1Σ+g states together with the X̃ 3Σ−g ground state for the first time. These low-lying singlet states are separated from the triplet ground state by 1.010±0.010 and 1.629±0.010 eV, respectively. We find a vibrational frequency of 1120±50 cm−1 for the υ1 mode of the b̃ 1Σ+g state. The ions were produced in a new source particularly suitable for anion precursors with low vapor pressure.