Raman study of solid N2O4: Temperature induced autoionization

Raman spectra of solid N2O4 condensed from gaseous NO2/N2O4 were investigated. When deposited at 80 K the O2NNO2 dimer is formed. Deposition at 15 K produces additionally bands of the NO2 monomer and the O2NONO isomers. Warming to 180 K induces autoionization to NO+NO−3 which remains stable over the 15–180 K range. The transition is probably an intermolecular process invoked through the low energy lattice modes or ν4 twist vibration of the dimer.