Ab initio study of the HO2+NO reaction: Prediction of the total rate constant and product branching ratios for the forward and reverse processes

Abstract

The mechanisms for HO2+NO and its reverse reactions have been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies refined by single-point calculations with the highest scheme of the modified Gaussian-2 method. Ab initio results show that formation of HO+NO2 from HO2+NO by the direct fragmentation of the peroxynitrous acid, HOONO intermediate, is predominant; the alternative path occurring by the isomerization of HOONO to HONO2 is 5.2 kcal/mol less favorable. The stepwise formation of HNO+O2 from HOONO is energetically unfavorable; the barriers for the direct H abstract reactions via singlet and triplet paths are found to be rather high also. Rate constant calculations show that the forward reaction is pressure independent below 10 atm; the reverse OH+NO2 reactions producing HONO2 and HOONO appear to be strongly pressure dependent; below 1 atm, the yield of HOONO from HO+NO2 is <2.5% at 300–400 K, it reaches 12.2% and 9.1%, respectively, at 300 and 400 K at 3.8×104 Torr pressure. The low- and high-pressure rate constants with He as a third-body for the formation of HOONO and HONO2 from the HO+NO2 reaction can be expressed by k0 (HOONO)=3.15×102 T−12.3 exp(−585/T), k0 (HONO2)=3.32×10−6 T−8.8 exp(−1569/T)cm6 molecule−2 s−1 and k∞ (HOONO)=1.71×10−10 T−0.24 exp(100/T) and k∞ (HONO2)=4.74×10−9 T−0.82 exp(21/T) cm3 molecule−1 s−1, respectively, in the temperature range of 200–2000 K. The unimolecular decomposition rate constant (in Ar) of HNO3 can be expressed as kd∞ (HNO3)=2.30×1023 T−2.27 exp(−26317/T) s−1 and kd0 (HNO3)=1.27×1015 T−6.55exp(−26038/T) cm3 molecule−1 s−1, respectively. The predicted values are all in close agreement with experimental data for both forward and reverse processes.

Atmospheric pressure dielectric barrier discharges interacting with liquid covered tissue

“…Atkinson et al [52] suggested that the production of HOONO in the gas phase cannot be ignored, and Nizkorodov and Wennberg [53] made spectroscopic observations of gas-phase HOONO. Both HNO 3 and HOONO are likely produced in the gas phase by reactions of NO 2 with OH, and NO with HO 2 as discussed above [54][55][56]. When OH reacts with the O atom in ONO (the same as NO 2 but representing the molecular structure), the linear molecule HOONO is produced.…”

“…In experiments [53,54], HOONO was determined by a ratio of HOONO/HNO 3 , which ranges from 5% to 30%. Rate coefficients for the reaction of OH and NO 2 , 1.57 × 10 −11 cm −3 s −1 ; and for the reaction of HO 2 and NO, 2.31 × 10 −13 cm −3 s −1 [55,56], produce a ratio of HOONO/HNO 3 of ≈40% in the gas phase. The production of HOONO and HNO 3 consumes a small portion of the NO and NO 2 .…”

Kinetics of the reactions of ONOO− with small molecules

“…In addition, the protonated form HOONO However, it was five years later when it was realized that this has been found to be important in atmospheric chemistry [8]. was a peroxide isomer and not the more stable D3h isomer with a These applications have resulted in a number of theoretical central N [2].…”

Influence of H2O and NH3 on the reaction of HO2 with NO in troposphere: Theoretical investigation of HNO3 formation pathways

“…Given the importance of the HO 2 + NO reaction in the atmosphere, several publications have been investigated, and as a result, the kinetics of this reaction has been studied experimentally [8][9][10][11][12][13] and theoretically [14][15][16][17][18][19][20][21] for a range of temperature. Meanwhile, as the significant enhancement [22][23][24] of H 2 O in the HO self-reaction is explained by the formation of the H 2 OÁÁÁHO 2 complex, a similar mechanism may occur in other HO 2 radical reactions, particularly in Equation (2).…”

“…HNO 3 ) and indirect [47,54] The B3LYP functional [55,56] has proven to be a reliable DFT method for describing the geometries, zero-point energies (ZPEs), and frequencies for the HO 2 + NO reaction in previous studies. [7,21] As a result, the geometries of all the stationary points, including reactants, complexes, transition states (TSs), and products for the HO 2 + NO reaction without and with medium X (X = H 2 O, (H 2 O) 2 , NH 3 , and H 3 NÁÁÁH 2 O), are optimized at the B3LYP/6-311 + G(2df,2p) level, carried out using the Gaussian 09 program package. [57] Harmonic vibrational frequencies have been calculated at the same level to determine the minimum energy equilibrium structures, which possess all real frequencies, while the TS has a single imaginary frequency.…”