Mass Spectrometric Study of Photoionization. VII. Nitrogen Dioxide and Nitrous Oxide

Photoionization efficiency curves are obtained for the molecule and fragment ions of NO₂ and N₂O from ionization threshold to 600 Å. Features of the molecule ion curves are ascribed to autoionization and the Rydberg levels are correlated with reported spectroscopic observations. The minimum onset of ionization for NO₂ occurs at 1272 Å (9.75 eV). The threshold value of 12.34 eV for the NO⁺ fragment results in D(NO-O) of 3.09 eV in good agreement with that calculated from thermochemical heats of formation. The 0⁺ ion is apparently formed with 0.1 eV excess energy. The minimum threshold energy for the N₂O⁺ ion is 962 Å (12.89 eV). The $$ fragment ion curve has a threshold at 17.29 eV corresponding to the thermochemical bond energy, D(N₂ - 0)= 1.67 eV. However a lower-energy threshold at 15.57 eV is ascribed to ionization of molecular nitrogen from an unknown source. There is no evidence for an ion-pair process. The ground state transition for NO⁺ is forbidden by spin conservation rules. The observed threshold is 0.8 eV in excess of the calculated value and suggests a vibrationally excited state of the ion. The N⁺ ion is also formed with excess energy.