Formation of N3O3− anion in (NO)n−: photoelectron spectroscopy and ab initio calculations

Photoelectron spectra of (NO)n− (1≤n≤7) were recorded at a photon energy of 4.66 eV, and the vertical detachment energies (VDEs) were determined as a function of the cluster size. The VDE shows an abrupt increase from 2.93±0.05 eV for n=2 to 3.70±0.02 eV for n=3. This large VDE shift is attributed to the formation of the N3O3− molecular anion, which acts as a core in the larger clusters; hence, the (NO)n− clusters with n≥3 are well described as N3O3−·(NO)n−3. Ab initio calculations at the MP2/6-31+G* level predict that the N3O3− molecular anion occurs with isomeric forms having either normal or branched chain configuration.