Theoretical Study on Mechanism of Reaction of OH with HO2NO2

The reaction of HO2NO2 (peroxynitric acid, PNA) with OH was studied by the hybrid density functional B3LYP and CBS-QB3 methods. Based on the calculated potential energy surface, five reaction channels, H2O+NO2+O2, HOOH+NO3, NO2+HO3H, HO2+HONO2 and HO2+HOONO, were examined in detail. The major reaction channel is PNA+OH→M1→TS1→H2O+NO2+O2. Taking a pre-equilibrium approximation and using the CBS-QB3 energies, the theoretical rate constant of this channel was calculated as 1.13×10-12 cm3/(molecule s) at 300 K, in agreement with the experimental result. Comparison between reactions of HOONO2+OH and HONO2+OH was carried out. For HOR+OH reactions, the total rate constants increase from R=NO2 to R=ONO2, which is consistent with experimental measurements.     

Atmospheric reaction of the HOSO radical with NO2: a theoretical study

The gas-phase reaction between HOSO and NO(2) was examined using density functional theory. Geometry optimizations and frequency computations were performed at the B3LYP/6-311++G(2df,2pd) level of theory for all minimum species and transition states. The ground-state potential energy surface, including activation energies and enthalpies, were calculated using the ab initio CBS-QB3 composite method. The results suggest that the addition of HOSO and NO(2) leads to two possible intermediates, HOS(O)NO(2) and HOS(O)ONO, without any energy barrier. The HOS(O)NO(2) easily decomposes into HONO + SO(2) through the low energy product complex HONO···SO(2), whereas the HOS(O)ONO dissociates to HOSO(2) + NO products. This latter dissociation is preferred from the isomerization of the HOS(O)ONO to HOS(NO)O(2). Also, HOS(O)NO(2) isomerization to HOS(O)ONO is hindered due to the presence of a large energy barrier. From the thermodynamic aspect, the main products in the title reaction are HONO + SO(2), whereas HOSO(2) + NO are expected as a minor products.     

In situ attenuated total reflection infrared (ATR-IR) study of the adsorption of NO2-, NH2OH, and NH4+ on Pd/Al2O3 and Pt/Al2O3

In relation to the heterogeneous hydrogenation of nitrite, adsorption of NO2-, NH4+, and NH2OH from the aqueous phase was examined on Pt/Al2O3, Pd/Al2O3, and Al2O3. None of the investigated inorganic nitrogen compounds adsorb on alumina at conditions presented in this study. NO2-(aq) and NH4+(aq) on the other hand show similar adsorption characteristics on both Pd/Al2O3 and Pt/Al2O3. The vibrational spectrum of the NO2- ion changed substantially upon adsorption, clearly indicating that NO2- chemisorbs onto the supported metal catalysts. On the contrary, adsorption of NH4+ does not lead to significant change in the vibrational spectrum of the ion, indicating that the NH4+ ion does not chemisorb on the noble metal but is stabilized via an electrostatic interaction. When comparing the adsorption of hydroxylamine (NH2OH(aq)) on Pd/Al2O3 and Pt/Al2O3, significant differences were observed. On Pd/Al2O3, hydroxylamine is converted into a stable NH2(ads) fragment, whereas on Pt/Al2O3 hydroxylamine is converted into NO, possibly via HNO(ads) as an intermediate.     

Potential role of the nitroacidium ion on HONO emissions from the snowpack

The effects of photolysis on frozen, thin films of water-ice containing nitrogen dioxide (as its dimer dinitrogen tetroxide) have been investigated using a combination of Fourier transform reflection-absorption infrared (FT-RAIR) spectroscopy and mass spectrometry. The release of HONO is ascribed to a mechanism in which nitrosonium nitrate (NO+NO3-) is formed. Subsequent solvation of the cation leads to the nitroacidium ion, H2ONO+, i.e., protonated nitrous acid. The pathway proposed explains why the field measurement of HONO at different polar sites is often contradictory.     

A theoretical ab initio study on the H(2)NO + O(3) reaction

The deviation of the NH(2) pseudo-first-order decay Arrhenius plots of the NH(2) + O(3) reaction at high ozone pressures measured by experimentalists, has been attributed to the regeneration of NH(2) radicals due to the subsequent reactions of the products of this reaction with ozone. Although these products have not yet been characterized experimentally, the radical H(2)NO has been postulated, because it can regenerate NH(2) radicals through the reactions: H(2)NO + O(3) --> NH(2) + O(2) and H(2)NO + O(3) --> HNO + OH + O(2). With the purpose of providing a reasonable explanation from a theoretical point of view to the kinetic observed behaviour of the NH(2) + O(3) system, we have carried ab initio electronic structure calculations on both H(2)NO + O(3) possible reactions. The results obtained in this article, however, predict that of both reactions proposed, only the H(2)NO + O(3) --> NH(2) + O(2) reaction would regenerate indeed NH(2) radicals, explaining thus the deviation of the NH(2) pseudo-first-order decay observed experimentally.     

Pressure dependence of pentyl nitrate formation from the OH Radical-initiated reaction of n-pentane in the presence of NO

The formation yields of 2- and 3-pentyl nitrate from the reactions of 2- and 3-pentyl peroxy radicals with NO have been measured at room temperature over the pressure range 51-744 Torr of N2 + O2, using the OH radical-initiated reaction of n-pentane to generate the pentyl peroxy radicals. The influence of 2- and 3-pentyl nitrate formation from the reaction of 2- and 3-pentoxy radicals with NO2 was investigated by conducting experiments with the initial CH3ONO (the OH radical precursor) and NO concentrations being varied by a factor of 5-10. From experiments carried out with low initial CH3ONO and NO concentrations, the measured yields of 2-pentyl nitrate and 3-pentyl nitrate, defined as ([pentyl nitrate] formed)/([n-pentane] reacted), each increase with increasing total pressure, from 1.10 +/- 0.09% and 1.11 +/- 0.10%, respectively, at 51 +/- 1 Torr of O2 to 5.48 +/- 0.51% and 4.07 +/- 0.31%, respectively, at 737 +/- 4 Torr of N2 + O2.     

Formation of nitrous acid and nitric oxide in the heterogeneous dark reaction of nitrogen dioxide and water vapor in a smog chamber

The dark reaction of NO_x and H₂O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO₂ and H₂O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO₂ and H₂O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO₂ and H₂¹⁸O gave H¹⁸ONO exclusively. Taking into consideration the heterogeneous reaction of NO₂ and H₂O, the upper limit of the rate constant of the third-order reaction NO + NO₂ + H₂O → 2HONO was deduced to be (3.0 ± 1.4) × 10^?10 ppm^?2-min^?1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO₂ and H₂O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.     

Theoretical mechanistic study on the radical-molecule reaction of CH2OH with NO2

The complex singlet potential energy surface for the reaction of CH2OH with NO2, including 14 minimum isomers and 28 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and Gaussian-3 (single-point) levels. The initial association between CH2OH and NO2 is found to be the carbon-to-nitrogen approach forming an adduct HOCH2NO2 (1) with no barrier, followed by C-N bond rupture along with a concerted H-shift leading to product P1 (CH2O + trans-HONO), which is the most abundant. Much less competitively, 1 can undergo the C-O bond formation along with C-N bond rupture to isomer HOCH2ONO (2), which will take subsequent cis-trans conversion and dissociation to P2 (HOCHO + HNO), P3 (CH2O + HNO2), and P4 (CH2O + cis-HONO) with comparable yields. The obtained species CH2O in primary product P1 is in good agreement with kinetic detection in experiment. Because the intermediate and transition state involved in the most favorable pathway all lie blow the reactants, the CH2OH + NO2 reaction is expected to be rapid, as is confirmed by experiment. These calculations indicate that the title reaction proceeds mostly through singlet pathways; less go through triplet pathways. In addition, a mechanistic comparison is made with the reactions CH3 + NO2 and CH3O + NO2. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO2-combustion chemistry.     

Computational study on the kinetics and mechanism for the unimolecular decomposition of C6H5NO2 and the related C6H5 + NO2 and C6H5O + NO reactions

The kinetics and mechanisms for the unimolecular dissociation of nitrobenzene and related association reactions C(6)H(5) + NO(2) and C(6)H(5)O + NO have been studied computationally at the G2M(RCC, MP2) level of theory in conjunction with rate constant prediction with multichannel RRKM calculations. Formation of C(6)H(5) + NO(2) was found to be dominant above 850 K with its branching ratio > 0.78, whereas the formation of C(6)H(5)O + NO via the C(6)H(5)ONO intermediate was found to be competitive at lower temperatures, with its branching ratio increasing from 0.22 at 850 K to 0.97 at 500 K. The third energetically accessible channel producing C(6)H(4) + HONO was found to be uncompetitive throughout the temperature range investigated, 500-2000 K. The predicted rate constants for C(6)H(5)NO(2) --> C(6)H(5) + NO(2) and C(6)H(5)O + NO --> C(6)H(5)ONO under varying experimental conditions were found to be in good agreement with all existing experimental data. For C(6)H(5) + NO(2), the combination processes producing C(6)H(5)ONO and C(6)H(5)NO(2) are dominant at low temperature and high pressure, while the disproportionation process giving C(6)H(5)O + NO via C(6)H(5)ONO becomes competitive at low pressure and dominant at temperatures above 1000 K.     

Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. II. The multilayer regime in interstellar relevant ices

Hydroxylamine (NH(2)OH) is one of the potential precursors of complex pre-biotic species in space. Here, we present a detailed experimental study of hydroxylamine formation through nitric oxide (NO) surface hydrogenation for astronomically relevant conditions. The aim of this work is to investigate hydroxylamine formation efficiencies in polar (water-rich) and non-polar (carbon monoxide-rich) interstellar ice analogues. A complex reaction network involving both final (N(2)O, NH(2)OH) and intermediate (HNO, NH(2)O[middle dot], etc.) products is discussed. The main conclusion is that hydroxyl-amine formation takes place via a fast and barrierless mechanism and it is found to be even more abundantly formed in a water-rich environment at lower temperatures. In parallel, we experimentally verify the non-formation of hydroxylamine upon UV photolysis of NO ice at cryogenic temperatures as well as the non-detection of NC- and NCO-bond bearing species after UV processing of NO in carbon monoxide-rich ices. Our results are implemented into an astrochemical reaction model, which shows that NH(2)OH is abundant in the solid phase under dark molecular cloud conditions. Once NH(2)OH desorbs from the ice grains, it becomes available to form more complex species (e.g., glycine and β-alanine) in gas phase reaction schemes.     

Approach to the atmospheric chemistry of methyl nitrate and methylperoxy nitrite. Chemical mechanisms of their formation and decomposition reactions in the gas phase

Potential energy surfaces, minimum energy reaction paths, minima, transition states, reaction barriers, and conical intersections for the most important atmospheric reactions of methyl nitrate (CH(3)ONO(2)) and methylperoxy nitrite (C(3)HOONO) on the electronic ground state have been studied (i) with the second-order multiconfigurational perturbation theory (CASPT2) by computation of numerical energy gradients for stationary points and (ii) with the density functional theory (DFT). The proposed mechanism explains the conversion of unreactive alkyl peroxy radicals into alkoxy radicals: CH(3)O(2) + NO <=> CH(3)OONO <=> CH(3)O + NO(2) left arrow over right arrow CH(3)ONO(2). Additionally, several discrepancies found in the comparison of the results obtained from the two employed approaches are analyzed. CASPT2 predicts that all dissociation reactions into radicals occur without an extra exit energy barrier. In contrast, DFT finds transition states for the dissociations of cis- and trans-methylperoxy nitrite into CH(3)O + NO(2). Furthermore, multiconfigurational methods [CASPT2 and complete active space SCF (CAS-SCF)] predict the isomerization of CH3ONO2 to CH3OONO to occur in a two-step mechanism: (i) CH(3)ONO(2) --> CH(3)O + NO(2); and (ii) CH(3)O + NO(2) --> CH(3)OONO. The reason for this has to do with the coupling of the ground electronic state with the first excited state. Therefore, it is demonstrated that DFT methods based on single determinantal wave functions give an incorrect picture of the aforementioned reaction mechanisms.     

Computational study on the kinetics and mechanisms for the reactions of HCO with HONO and HNOH

The kinetics and mechanisms of the HCO reactions with HONO and HNOH have been studied at the G2M level of theory based on the geometric parameters optimized at BH&HLYP/6‐311G(d,p). The rate constants in the temperature range 200–3000 K at different pressures have been predicted by microcanonical RRKM and/or variational transition state theory calculations with Eckart tunneling corrections. For the HCO + HONO reaction, hydrogen abstraction from trans‐HONO and cis‐HONO by HCO produces H₂CO + NO₂, with the latter being dominant. Two other channels involving cis‐HONO by the association/decomposition mechanism via the HC(O)N(O)OH intermediate, which could fragment to give H₂O + CO + NO at high temperatures, were also found to be important. For the HCO + HNOH reaction, three reaction channels were identified: one association reaction giving a stable intermediate, HC(O)N(H)OH (LM2), and two hydrogen abstraction channels producing H₂CO and H₂NOH. The dominant products were predicted to be the formation of LM2 at low temperatures and H₂NOH + CO at middle and high temperatures. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 178–187 2004     

Quasiclassical trajectory calculations of the OH+NO2 association reaction on a global potential energy surface

We report a full-dimensional potential energy surface (PES) for the OH+NO(2) reaction based on fitting more than 55,000 energies obtained with density functional theory-B3LYP6-311G(d,p) calculations. The PES is invariant with respect to permutation of like nuclei and describes all isomers of HOONO, HONO(2), and the fragments OH+NO(2) and HO(2)+NO. Detailed comparison of the structures, energies, and harmonic frequencies of various stationary points on the PES are made with previous and present high-level ab initio calculations. Two hydrogen-bond complexes are found on the PES and confirmed by new ab initio CASPT2 calculations. Quasiclassical trajectory calculations of the cross sections for ground rovibrational OH+NO(2) association reactions to form HOONO and HONO(2) are done using this PES. The cross section to form HOONO is larger than the one to form HONO(2) at low collision energies but the reverse is found at higher energies. The enhancement of the HOONO complex at low collision energies is shown to be due, in large part, to the transient formation of a H-bond complex, which decays preferentially to HOONO. The association cross sections are used to obtain rate constants for formation of HOONO and HONO(2) for the ground rovibrational states in the high-pressure limit.     

铊(I)离子选择电极动力学分析法测定超痕量铁

Fe(II) induces the reaction between Tl3+ and H2O2. The rate of reaction is linearly proportional to the concentration of Fe2+ in the range 2.5 ?10-9-2.5 ?10-8 mol dm-3 (20? and 5 ?10-9-5 ?10-8 mol dm-3 (15?. The standard deviation is less than 0.071 ?10-8. A 1000-fold excess of Zn2+, Cd2+, Mg2+, Ni2+, Pb2+, Ba2+, Ca2+, Li+, Na+, Ag+, NO3-, SO42-, AcO-, HPO42-, 500-fold excess of Al3+, Fe3+, Co2+, Hg2+ and 100-fold excess of Ti4+, Cr3+, Cu2+, Br-, Cl- can be tolerated, but reducing agents such as (NH2)2SO4, NH2OH.HCl interfered. This kinetic method was applied to determine Fe(II) in standard zinc sample and fountain water, with satisfactory results.     

Rotational state-resolved reaction cross section in the reactions of state-selected CH with NO and with O2

A pure and highly intense state-selected pulsed supersonic CH(X (2)Pi) radical beam source was developed by use of the C((1)D)+H(2) reaction with the combination of the state selection and purification by an electrostatic hexapole field. Under the beam-cell condition, the elementary reactions of CH+NO and CH+O(2) were studied by using this state-selected CH beam. NH(A (3)Pi) [and NCO(A (2)Sigma(+))] formations and OH(A (2)Sigma(+)) formation were directly identified in the elementary reaction of CH+NO and CH+O(2), respectively. For the CH+NO reaction, the relative branching ratio sigma(NCO*)sigma(NH) of NCO(A (2)Sigma(+)) formation to NH(A (3)Pi) formation was determined to be 0.35+/-0.15. The state-selected reaction cross sections were determined for each rotational state of CH. In the CH+NO reaction, a remarkable rotational state dependence of the reactive cross section was revealed, while the CH+O(2) reaction showed little rotational state dependence.     

多反应离子的质子转移反应质谱

在无放射性辉光放电离子源内, 采用不同试剂气体进行放电, 为质子转移反应质谱(PTR-MS)新增了强度在10⁵ cps量级的3种反应离子NH₄⁺, NO⁺和O₂⁺, 纯度大于95%; 测试了这3种反应离子的离子-分子反应特征. 采用H₃O⁺, NH₄⁺, NO⁺和O₂⁺等4种反应离子对同分异构体丙醛/丙酮进行检测发现, H₃O⁺和NH₄⁺均不能区分的丙醛/丙酮可采用NO⁺或O₂⁺进行区分. 结果表明, 增加反应离子不仅使PTR-MS的可检测有机物范围不再局限于质子亲和势(PA)大于H₂O的有机物, 还提高了PTR-MS区分同分异构体的能力.     

Nitrosyl induces phosphorous-acid dissociation in ruthenium(II)

The trans-[Ru(NO)(NH(3))(4)(P(OH)(3))]Cl(3) complex was synthesized by reacting [Ru(H(2)O)(NH(3))(5)](2+) with H(3)PO(3) and characterized by spectroscopic ((31)P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol(-1) cm(-1); λ = 319 nm, ε = 773 L mol(-1) cm(-1); λ = 241 nm, ε = 1385 L mol(-1) cm(-1); ν(NO(+)) = 1879 cm(-1)). A pK(a) of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) + H(2)O ? trans-[Ru(NO)(NH(3))(4)(P(O(-))(OH)(2))](2+) + H(3)O(+). According to (31)P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) yields the O-bonded linkage isomer trans- [Ru(NO)(NH(3))(4)(OP(OH)(2))](2+), then the trans-[Ru(NO)(NH(3))(4)(OP(H)(OH)(2))](3+) decays to give the final products H(3)PO(3) and trans-[Ru(NO)(NH(3))(4)(H(2)O)](3+). The dissociation of phosphorous acid from the [Ru(NO)(NH(3))(4)](3+) moiety is pH dependent (k(obs) = 2.1 × 10(-4) s(-1) at pH 3.0, 25 °C).     

New insights in the atmospheric HONO formation: new pathways for N2O4 isomerization and NO2 dimerization in the presence of water

Isomerization of N(2)O(4) and dimerization of NO(2) in thin water films on surfaces are believed to be key steps in the hydrolysis of NO(2), which generates HONO, a significant precursor to the OH free radical in lower atmosphere and high-energy materials. Born-Oppenheimer molecular dynamics simulations using the density functional theory are carried out for NO(2)(H(2)O)(m), m ≤ 4, and N(2)O(4)(H(2)O)(n) clusters, n ≤ 7, used to mimic the surface reaction, to investigate the mechanism around room temperature. The results are (i) the NO(2) dimerization and N(2)O(4) isomerization reactions occur via two possible pathways, the non-water-assisted and water-assisted mechanisms; (ii) the NO(2) dimerization in the presence of water yields either ONONO(2)(H(2)O)(m) or NO(3)(-)NO(+)(H(2)O)(m) clusters, but it is also possible to form the HNO(3)(NO(2)(-))(H(3)O(+))(H(2)O)(m-2) transition state to form HONO and HNO(3), directly; (iii) the N(2)O(4) isomerization yields the NO(3)(-)NO(+)(H(2)O)(n) cluster, but it does not hydrolyze faster than the NO(2)(+)NO(2)(-)(H(2)O)(n) hydrolysis to directly form the HONO and HNO(3). New insights for hydrolysis of oxides of nitrogen in and on thin water films on surfaces in the atmosphere are discussed.     

潮湿空气微波放电离子形成动力学

利用微波放电电离质谱装置，通过水蒸气与空气混合气体（潮湿空气）的微波放电，同时获得了化学电离质谱探测技术中常用的三种重要母体离子H3O＋、NO＋和.结合潮湿空气中主要成分N2、O2以及水蒸气各自微波放电后的质谱探测结果，对潮湿空气微波放电后上述三种离子产生的动力学过程进行了分析，并给出了各种离子的形成机制.这些离子 分子反应过程在计算机模拟中得到了进一步的证实.     

Theoretical study on the reaction mechanism of NH2(-) with O2 (a1Δg)

A detailed theoretical study of the potential energy surface of poorly understood ion-molecule reaction of NH(2)(-) and O(2) (a(1)Δ(g)) is explored at the density functional theory B3LYP/6-311++G(d,p), ab initio of QCISD/6-311++G(d,p) and CCSD(T)/6-311++G(3df, 2pd) (single-point) theoretical levels for the first time. It is shown that there are six total possible products from P(1) to P(6) on the singlet potential energy surface. Among these, the charge-transfer product P(1) (NH(2) + O(2)(-)) is the most favorable product with predominant abundances, whereas P(4) (NO(-) + H(2)O) and P(2) (HNO + OH(-)) may be the second and third feasible products followed by the almost neglectable P(3) (NO(2)(-) + H(2)), while P(5) (c-NO(2)(-) + H(2)) and P(6) (ONO(-) + H(2)) will not be observed due to their either high barriers or being secondary products. The present theoretical study points out that besides P(1) (NH(2) + O(2)(-)) and P(2) (HNO + OH(-)), P(4) (NO(-) + H(2)O) should be also observed, which is different from the previous experiment study by Anthony Midey et al. in 2008. In addition, almost all of the reaction pathways to products are exothermic and the reaction rate should be very fast since the reaction barriers are very low except for P(5) (c-NO(2)(-) + H(2)) which is in agreement with the measured total reaction rate constant k = 9.0 × 10(-10) cm(3)s(-1) at 300 K in the experiment study. It is expected that the present theoretical study may be helpful for the understanding of the reaction mechanism related to NHX(-), NX(2)(-), PHX(-), and PX(2)(-) (X = H, F, and Cl).