Mass Spectrometric and Computational Study of Gaseous Peroxynitric Acid and (HOONO2)H+ Protomers

The positive ion chemistry of peroxynitric acid (1) was investigated in the gas phase by mass-analyzed ion kinetic, collisionally activated dissociation, and Fourier transform-ion cyclotron resonance mass spectrometric techniques and theoretical methods up to the B3LYP/6-311++g(3df,2pd) and G2, i.e. QCISD(T)/6-311+g(3df,2pd), levels. The ion-neutral complex HOOH-NO2/+ (1a) is the only detectable protomer in CI experiments involving the protonation of 1 by H3O+, and can also be obtained from the reaction of NO2/+ with H2O2 1a behaves as a protonating and nitrating agent toward gaseous nucleophiles. The experimental proton affinity of 1 is estimated to be 176 ± 3 kcal mol-1, in excellent agreement with the 175 ± 2 kcal mol-1 G2 PA. The theoretical results show that 1a is more stable than the HOONO2H+ (1b) and the H2OONO2/+ (1c) protomers by 13 and 16 kcal mol-1, respectively, at the B3LYP level of theory, and account for the exclusive formation of 1a in the CI experiments. The experimental and B3LYP theoretical binding energy of NO2/+ to H2O2 amounts to 18 ± 2 kcal mol-1. (C) 2000 Elsevier Science B.V.