Chemiluminescent spectra of HNO and DNO in the reaction of O(3P)/O2 with NO and hydrocarbons of aldehydes

The chemiluminescent emission from the electronically excited state of HNO (¹A″) was observed in the reactions of O(³P)/O₂ with NO and one of acetylene, ethylene, propylene, formaldehyde and acetaldehyde. The identification of the emitting species was confirmed by observing the emission from DNO in the reactin of O/O₂ with NO and ethylene-d₄. The emission spectra were different from those observed in the reaction of H(D) + NO + M.     

Vibrational emission of NO2 from the reaction of NO with O3

Vibrational chemiluminescence in the Δν₁ = Δν₃ = ?1 band of NO₂ is observed both in the O + NO and O₃ + NO reactions and shown to be emitted by molecules with up to 11 000 cm^?1 of vibrational energy. Quenching rate constants of NO₂³ are estimated ranging from about 6 × 10^?14 for Ar to about 3 × 10^?12 cm³ s^?1 for NO₂. The ratio of vibrational to electronic emission is 0.06 ± 0.03 for O + NO and 5.3 ± 1.0 for O₃ + NO. It is suggested that vibrationally excited NO₂ is a major product of that channel of the O₃ + NO reaction which forms ground-state NO₂(²A₁) directly.     

Not Limited to Iron: A Cobalt Heme–NO Model Facilitates N–N Coupling with External NO in the Presence of a Lewis Acid to Generate N2O

Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N₂O. We previously reported that a heme Fe–NO model engages in this N?N bond‐forming reaction with NO. We now demonstrate that (OEP)Co^II(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX₃ (X=F, C₆F₅) to generate N₂O. DFT calculations support retention of the Co^II oxidation state for the experimentally observed adduct (OEP)Co^II(NO?BF₃), the presumed hyponitrite intermediate (P^.+)Co^II(ONNO?BF₃), and the porphyrin π‐radical cation by‐product of this reaction, and that the π‐radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous‐to‐ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO‐to‐N₂O conversion reaction.     

基于赤铁矿的生物质化学链燃烧过程中氮氧化物的释放特性

在单批次进料固定床上,基于赤铁矿载氧体,研究了还原反应阶段反应温度和水蒸气量对谷壳的氮氧化物释放特性的影响。研究表明,碳转化率随反应温度升高而增加,但随水蒸气量呈先增加后下降,并在水蒸气量为1.0 g/min时达到最大值。在实验条件下,还原阶段未检测到NO₂。随着反应温度由750 ℃升高到900 ℃,NO的生成率增加,而N₂O的生成率先增加后降低,在850 ℃时达到最大值。水蒸气量由0.5 g/min升高到2.0 g/min,N₂O和NO的生成率均增加,且NO增加速率高于N₂O。在反应后的载氧体中,检测到KAlSi₃O₈存在,表明载氧体与生物质中的K元素发生反应。     

The two-photon excitation spectrum of triphenylene in n-heptane single crystals: Chem. Phys. Letters 57 (1978) 496

Chemiluminescence spectra and photon yields resulting from reactions of copper atoms with N₂O, O₂, NO, NF₃, SF₆, F₂, Cl₂, Br₂, and I₂ have been obtained between 200 and 1100 nm. The most interesting feature of these spectra is the strong and peculiar emission from copper atoms observed in the Cu + NF₃ reaction; population inversion has been obtained between some of the Cu states and it is suggested that this is due to energy transfer from N₂(A) formed in the reaction to copper atoms.     

Experimental Study of C2Cl3+NO2 Reaction

The free radical reaction of C2Cl3 with NO2 was investigated by step-scan time-resolved FTIR (TR-FTIR) emission spectroscopy. Due to the vibrationally excited products of Cl2CO, NO, and CO, strong IR emission bands were observed with high resolution TR-FTIR spectra. Four reaction channels forming C2Cl3O+NO, CCl3CO+NO, CO+NO+CCl3, and ClCNO+Cl2CO were elucidated, respectively. Spectralˉtting showed that the product CO was highly vibrationally excited with the nascent average vibrational energy of 60.2 kJ/mol. Possible reaction mechanism via intermediates C2Cl3NO2 and C2Cl3ONO was proposed.     

Decomposition of nitrogen and dinitrogen oxides on copper and copper(I) oxide in elemental analysis by reaction gas chromatography

The decomposition of NO and N₂O on Cu and Cu₂O packings was studied in view of the simultaneous determination of N and S in organic compounds by the Pregl-Dumas method in a system of reaction gas chromatography, and the mass balance of the reactions taking place was carried out. The amounts of NO and N₂O that are decomposed on the reduction packing at temperatures within 883 and 1263 °K are quoted. The reduction activity of both packings toward NO decreases with increasing temperature, while both the reduction and sorption activity of Cu₂O is markedly lower than that of the Cu one. No significant sorption of NO was observed at temperatures within 883 and 923 °K and no sorption of gaseous N₂ and N₂O occurred on either packing.     

15N CIDNP investigations of the peroxynitric acid nitration of L-tyrosine and of related compounds

Peroxynitric acid (O2NOOH) nitrates L-tyrosine and related compounds at pH 2-5. During reaction with O2(15)NOOH in the probe of a 15N NMR spectrometer, the NMR signals of the nitration products of L-tyrosine, N-acetyl-L-tyrosine, 4-fluorophenol and 4-methoxyphenylacetic acid appear in emission indicating a nitration via free radicals. Nuclear polarizations are built up in radical pairs [15NO2* , PhO*]F or [15NO2* , ArH*+]F formed by diffusive encounters of 15NO2 with phenoxyl-type radicals PhO or with aromatic radical cations ArH*+. Quantitative 15N CIDNP investigations with N-acetyl-L-tyrosine and 4-fluorophenol show that the radical-dependent nitration is the only reaction pathway. During the nitration reaction, the 15N NMR signal of 15NO3- also appears in emission. This is explained by singlet-triplet transitions in radical pairs [15NO2* , 15NO3*]S generated by electron transfer between O2(15)NOOH and H15NO2 formed as a reaction intermediate. During reaction of peroxynitric acid with ascorbic acid, 15N CIDNP is again observed in the 15N NMR signal of 15NO3- showing that ascorbic acid is oxidized by free radicals. In contrast to this, O2(15)NOOH reacts with glutathione and cysteine without the appearance of 15N CIDNP, indicating a direct oxidation without participation of free radicals.     

Isotope exchange between NO and H2O on a platinum-containing catalyst based on fiberglass

The dynamics of ¹⁸O isotope exchange between NO or H₂O and a catalyst and the dynamics of ¹⁸O label transfer from NO to H₂O have been studied under conditions of sorption-desorption equilibrium. The occurrence of a reaction of oxygen exchange between NO and water sorbed in the bulk of the catalyst was detected. This reaction occurs at platinum sites with the participation of acid sites of the glass matrix. The rate constants of the reaction of NO with platinum sites and the diffusion coefficients of water in the bulk of the glass matrix are evaluated.     

Infrared multiphoton dissociation of methyl nitrite

Methyl nitrite undergoes dissociation when irradiated with the focused output of a pulsed CO₂ TEA laser. Time resolved infrared emission is observed and attributed to vibrationally excited formaldehyde and methanol. These species are produced via reactions of methoxy radicals formed in the primary dissociation. Other products formed are NO and N₂O.     

Theoretical study on the reaction mechanism of NO and CO catalyzed by Rh atom

The gas-phase reaction mechanism of NO and CO catalyzed by Rh atom has been systematically investigated on the ground and first excited states at CCSD(T)//B3LYP/6-311+G(2d), SDD level. This reaction is mainly divided into two reaction stages, NO deoxygenation to generate N₂O and then the deoxygenation of N₂O with CO to form N₂ and CO₂. The crucial reaction step deals with the NO deoxygenation to generate N₂O catalyzed by Rh atom, in which the self-deoxygenation of NO reaction pathway is kinetically more preferable than that in the presence of CO. The minimal energy reaction pathway includes the rate-determining step about N–N bond formation. Once the NO deoxygenation with CO catalyzed by rhodium atom takes place, the reaction results in the intermediate RhN. Then, the reaction of RhN with CO is kinetically more favorable than that with NO, while both of them are thermodynamically preferable. These results can qualitatively explain the experimental finding of N₂O, NCO, and CN species in the NO + CO reaction. For the N₂O deoxygenation with CO catalyzed by rhodium atom, the reaction goes facilely forward, which involves the rate-determining step concerning CO₂ formation. CO plays a dominating role in the RhO reduction to regenerate Rh atom. The complexes, OCRhNO, RhON₂, RhNNO, ORhN₂, RhCO₂, RhNCO, and ORhCN, are thermodynamically preferred. Rh atom possesses stronger capability for the N₂O deoxygenation than Rh⁺ cation.     

Elucidation of the Surprising Role of NO in N2O Decomposition over FeZSM-5

The decomposition of N₂O is strongly promoted by NO over steam-activated FeZSM-5. The promoting effect of NO is catalytic, and in addition to NO₂, ₂ is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N₂O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N₂O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N₂O. The latter sites seem to be remote from each other. Transient experiments using in situ FT-IR/MS and Multitrack over FeZSM-5 further elucidate the mechanism of NO promotion. The release of oxygen from the catalyst surface during direct N₂O decomposition is a rate-determining step due to the slow oxygen recombination, which is favored by high reaction temperatures. NO addition promotes this oxygen desorption, acting as an oxygen transfer agent, probably via NO₂ species. Adsorbed NO may facilitate the migration of atomic oxygen to enhance their recombination. Less than 0.9% of Fe seems to participate in this promotion. A model is proposed to explain the phenomena observed in NO-assisted N₂O decomposition, including NO₂ decomposition.     

Kinetic modeling of the reduction of nitric oxide in combustion products by isocyanic acid

The RAPRENO_x process for NO reduction in combustion products involves reaction of nitric oxide with isocyanic acid. We have developed a mechanism for the gas-phase reaction of isocyanic acid with nitric oxide in the presence of various amounts of O₂, H₂O, and CO. Kinetics calculations using the mechanism are compared with the experimental data of Siebers and Caton, and the model reproduces all trends of these data. Sensitivity and rate-of-production analyses show that the reactions of HNCO with OH, O, and H play a major role in the NO-removal process and that NO removal occurs primarily by reaction of NO with NCO to form N₂O, which subsequently reacts slowly to form N₂. The overall reaction is critically dependent on production of radicals. When O₂, H₂O, and CO are present, the radicals are supplied by the moist-CO chain branching sequence. When any of these species is absent, radicals must be supplied by other reactions, principally the N₂O decomposition reaction and the reaction of the NH₂ radical with NO.     

The heterogeneous formation of N2O in the presence of acidic solutions: Experiments and modeling

We investigated the heterogeneous processes that contribute towards the formation of N₂O in an environment that comes as closely as possible to exhaust conditions containing NO and SO₂ among other constituents. The simultaneous presence of NO, SO₂, O₂, and condensed phase water in the liquid state has been confirmed to be necessary for the production of significant levels of N₂O. The maximum rate of N₂O formation occurred at the beginning of the reaction and scales with the surface area of the condensed phase and is independent of its volume. The replacement of NO by either NO₂ or HONO significantly increases the rate constant for N₂O formation. The measured reaction orders in the rate law change depending upon the choice of the nitrogen reactant used and were fractional in some cases. The rate constants of N₂O formation for the three different nitrogen reactants reveal the following series of increasing reactivity: NO < NO₂ < HONO, indicating the probable sequential involvement of those species in the elementary reactions. Furthermore, we observed a complex dependence of the rate constant on the acidity of the liquid phase where both the initial rate as well as the yield of N₂O are largest at pH=0 of a H₂SO₄/H₂O solution. The results suggest that HONO is the major reacting N(III) species over a wide range of acidities studied. The N₂O formation in synthetic flue gas may be simulated using a relatively simple mechanism based on the model of Lyon and Cole. The first step of the complex overall reaction corresponds to NO oxidation by O₂ to NO₂ mainly in the gas phase, with the presence of both H₂O and active surfaces significantly accelerating NO₂ production. Subsequently, NO₂ reacts with excess NO to obtain HONO which reacts with S(IV) to result in N₂O and H₂SO₄ through a complex reaction sequence probably involving nitroxyl (HON) and its dimer, hyponitrous acid. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29 : 869–891, 1997.     

A Study on the Reaction of O(1D) and N2O by Trajectory Calculation and Time-Resolved FTIR Spectroscopy

O(¹D) atoms, generated via the laser photodissociation of N₂O at 193 nm, reacting with N₂O was studied by Time-Resolved Fourier Transform Infrared (TR-FTIR) Spectroscopy. The IR emission from NO(v? 1–11.) was collected at 30 μs after the laser was fired. Several instrumental corrections were made to obtain reliable experimental results. The vibrational temperature of the nearly-nascent NO product was estimated to be Tv ? 9,000 K. A Quasi-Classical Trajectory (QCT) calculation of the reaction was performed. The calculated results, corresponding to a head-on attack mechanism, agree with the experimental data. Additional reaction channel with side-on attack producing N₂ and O₂ was also studied by QCT, where vibrationally hot O₂(a ¹ Δ_g) and cold N₂(X¹∑_g⁺) products are predicted.     

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.     

Infrared emission following photolysis of methylisothiocyanate and methylthiocyanate

Methylisothiocyanate (CH(3)NCS) was photolyzed at 193 and 248 nm, and the resulting time-resolved infrared emission was observed. Similar experiments were performed on methylthiocyanate (CH(3)SCN) photolyzed at 193 nm. Previous work suggested that these isomers undergo excited-state isomerization prior to dissociation, but other experiments have contradicted this claim. In the infrared emission experiments, we observed the same products from both starting materials, supporting the theory of excited-state isomerization prior to dissociation. Methylisothiocyanate is the active ingredient in a widely used pesticide and has been observed to form highly toxic methyl isocyanate (CH(3)NCO) under environmental conditions. The mechanism for this formation has been unclear, but must involve some oxygen-containing species. At 248 nm, methylisothiocyanate was photolyzed alone and with three atmospheric oxidizers: O(2), NO, and NO(2). No chemical reaction was observed with O(2), whereas secondary reactions were observed with NO and NO(2). When methylisothiocyanate was photolyzed with NO(2), methyl isocyanate (CH(3)NCO) was observed, suggesting a likely environmental mechanism for methyl isocyanate formation.     

Nitric Oxide Disproportionation Mediated by a Rh Complex with an Asymmetric Pincer Ligand: Spectroscopic Detection of a Dinitrosyl Intermediate

The disproportionation of nitric oxide was studied by FTIR with two different Rh(I)PCN complexes as mediators (PCN 1-((diethylamino)methyl)-3-((di-tertbutylphosphino)methyl)-benzene). As had already been reported for a PCP analogue, reaction yielded a Rh(PCN)(NO)(NO₂) complex along with gaseous N₂O in both cases. However, when [Rh(PCN)(NO)]⋅ was used as a reactant, FTIR monitoring allowed for the detection of signals of a reaction intermediate, coherent with the expected but seldom reported dinitrosyl species Rh(PCN)(NO)(NO). DFT studies on this species revealed that pincer hemilability of the amino arm is involved in its stabilization, therefore accounting for the differences observed in reactivity between PCN and PCP.     

The vinyl + NO reaction: determining the products with time-resolved Fourier transform spectroscopy

We have studied the vinyl + NO reaction using time-resolved Fourier transform emission spectroscopy, complemented by electronic structure and microcanonical RRKM rate coefficient calculations. To unambiguously determine the reaction products, three precursors are used to produce the vinyl radical by laser photolysis: vinyl bromide, methyl vinyl ketone, and vinyl iodide. The emission spectra and theoretical calculations indicate that HCN + CH2O is the only significant product channel for the C2H3 + NO reaction near room temperature, in contradiction to several reports in the literature. Although CO emission is observed when vinyl bromide is used as the precursor, it arises from the reaction of NO with photofragments other than vinyl. This conclusion is supported by the absence of CO emission when vinyl iodide or methyl vinyl ketone is used. Prompt emission from vibrationally excited NO is evidence of the competition between back dissociation and isomerization of the initially formed nitrosoethylene adduct, consistent with previous work on the pressure dependence of this reaction. Our calculations indicate that production of products is dominated by the low energy portion of the energy distribution. The calculation also predicts an upper bound of 0.19% for the branching ratio of the H2CNH + CO channel, which is consistent with our experimental results.     

Study of the HNO + HNO and HNO + NO reactions by intracavity laser spectroscopy

Flash photolysis of CH₃CHO and H₂CO in the presence of NO has been investigated by the intracavity laser spectroscopy technique. The decay of HNO formed by the reaction HCO + NO → HNO + CO was studied at NO pressures of 6.8–380 torr. At low NO pressure HNO was found to decay by the reaction HNO + HNO → N₂O + H₂O. The rate constant of this reaction was determined to be k₁ = (1.5 ± 0.8) × 10^?15 cm³/s. At high NO pressure the reaction HNO + NO → products was more important, and its rate constant was measured to be k₂ = (5 ± 1.5) × 10^?19 cm³/s. NO₂ was detected as one of the products of this reaction. Alternative mechanisms for this reaction are discussed.