NOO peroxy isomer exposed with velocity-map imaging

The chemistry of NO2, a key atmospheric trace gas, has historically been interpreted in terms of the C2v isomer ONO, with the peroxy isomer NOO only postulated to be stable. In this work, a velocity-map-imaged photoelectron spectrum of the nitrite anion, NO2–, reveals energetic-electron structure that may only occur by photodetachment from the NOO–(X1A′) isomer. This measurement defines NOO(X2A′) bond frequencies and an electron affinity of only 335(30) cm–1, which, supported by ab initio calculations, confirm the first observation of this important reactive species.