10024-97-2Relevant articles and documents
Kinetics and mechanism of the iron phthalocyanine catalyzed reduction of nitrite by dithionite and sulfoxylate in aqueous solution
Kudrik, Evgeny V.,Makarov, Sergei V.,Zahl, Achim,Van Eldik, Rudi
, p. 6470 - 6475 (2005)
The reactions of sodium nitrite with sodium dithionite and sulfoxylate ion were studied in the presence of iron(III) tetrasulfophthalocyanine, Fe III(TSPc)3-, in aqueous alkaline solution. Kinetic parameters for the different reaction steps in the catalytic reduction by dithionite were determined. The final product of the reaction was found to be nitrous oxide. Contrary to this, the product of the catalytic reduction of nitrite by sulfoxylate was found to be ammonia. The striking difference in the reaction products is accounted for in terms of different structures of the intermediate complexes formed during the reduction by dithionite and sulfoxylate, in which nitrite is suggested to coordinate to the iron complex via nitrogen and oxygen, respectively. Sulfoxylate is shown to be a convenient reductant for the synthesis of the highly reduced iron phthalocyanine species FeI(TSPc?)6- in aqueous solution. The kinetics of the reduction of FeI(TSPc)5- to Fe I(TSPc?)6-, as well as the oxidation of the latter species by nitrite, was studied in detail.
Investigation of N2O production from 266 and 532 nm laser flash photolysis of O3/N2/O2 mixtures
Estupinan,Nicovich,Li,Cunnold,Wine
, p. 5880 - 5890 (2002)
Tunable diode laser absorption spectroscopy has been employed to measure the amount of N2O produced from laser flash photolysis of O3/N2/O2 mixtures at 266 and 532 nm. In the 532 nm photolysis experiments very little N2O is observed, thus allowing an upper limit yield of 7 × 10-8 to be established for the process O3? + N2 → N2O + O2, where O3? is nascent O3 that is newly formed via O(3PJ) + O2 recombination (with vibrational excitation near the dissociation energy of O3). The measured upper limit yield is a factor of ~600 smaller than a previous literature value and is approximately a factor of 10 below the threshold for atmospheric importance. In the 266 nm photolysis experiments, significant N2O production is observed and the N2O quantum yield is found to increase linearly with pressure over the range 100-900 Torr in air bath gas. The source of N2O in the 266 nm photolysis experiments is believed to be the addition reaction O(1D2) + N2 + M k6 → N2O + M, although reaction of (very short-lived) electronically excited O3 with N2 cannot be ruled out by the available data. Assuming that all observed N2O comes from the O(1D2) + N2 + M reaction, the following expression describes the temperature dependence of k6 (in its third-order low-pressure limit) that is consistent with the N2O yield data: k6 = (2.8 ± 0.1) × 10-36(T/300)-(0.88±0.36) cm6 molecule-2s-1, where the uncertainties are 2σ and represent precision only. The accuracy of the reported rate coefficients at the 95% confidence level is estimated to be 30-40% depending on the temperature. Model calculations suggest that gas phase processes initiated by ozone absorption of a UV photon represent about 1.4% of the currently estimated global source strength of atmospheric N2O. However, these processes could account for a significant fraction of the oxygen mass-independent enrichment observed in atmospheric N2O, and they appear to be the first suggested photochemical mechanism that is capable of explaining the altitude dependence of the observed mass-independent isotopic signature.
Reactivity of Rh+(CO)2 during the NO-CO and CO-O2 Reactions over Rh/Al2O3
Almusaiteer, Khalid A.,Chuang, Steven S. C.,Tan, Cher-Dip
, p. 247 - 247 (2000)
Exposure of Rh+(CO)2 on Rh/Al2O3 to NO causes CO desorption and adsorption of NO as Rh-NO+; exposure of Rh+(CO)2 to NO/H2 produced N2O at 573 K. The presenc
Pd/NaY-zeolite and Pd-W/NaY-zeolite catalysts: Preparation, characterization and NO decomposition activity
Pergher, Sibele B.C.,Dallago, Rogerio M.,Veses, Renato Cataluna,Gigola, Carlos E.,Baibich, Ione M.
, p. 107 - 115 (2004)
Pd/NaY-zeolite and Pd-W/NaY-zeolite catalysts were prepared from the compounds Pd(NO3)2 and [W(CO)6]. Tungsten was added by photochemical activation of [W(CO)6] to obtain a Pd-W interaction. The prepared catalysts were active for NO decomposition at 573 K leading mainly to N2 and N2O. NO conversion and the selectivity to N2O were studied as a function of time and the reduction temperature. The Pd/NaY-zeolite and the Pd-W/NaY-zeolite samples showed an initial period of high and constant activity followed by deactivation. Tungsten prevented the sintering of small Pd particles. Bimetallic sample deactivated faster, indicating that the Pd-W interaction decreased the fraction of exposed Pd atoms. The onset of N2O formation was in accord with the initiation of the deactivation.
Rate constants for formation of NO in vibrational levels v=2 through 7 from the reaction N(4S) + O2 -> NO* + O
Rahbee, A.,Gibson, J. J.
, p. 5143 - 5148 (1981)
Vibration-rotation spectra of the Δv=2 sequence of the nitric oxide formed by the chemiluminescent reaction N(4S) + O2 -> NO(X2Π) + O have been obtained with a spectral resolution of 15 cm-1.Emission bands due to N2O were observed to occur in the same spectral region as the first overtone of NO.These were experimentally eliminated and the resulting NO spectra were used to derive rate constants for formation of NO in vibrational levels v=2 through v=7.In units of 10-19 cm3/sec, these room temperature rate constants are, respectively, 55 +/- 14, 57 +/- 9, 33 +/- 3, 24 +/- 4, 7 +/- 2, and 5 +/- 2.Of all the nitric oxide molecules formed in the reaction, only 18percent are formed in levels v > 2.In terms of energy, of the 1.39 eV exothermicity of the reaction, about 10 percent goes into vibrational energy in levels v > 2.
Stabilization of ammonium dinitramide in the liquid phase
Andreev,Anikin,Ivanov,Krylov,Pak
, p. 1974 - 1976 (2000)
The kinetics of accumulation of the main products of thermal decomposition of ammonium dinitramide in the melt was investigated. The isotope composition of nitrogen-containing gases evolved by the decomposition of 15NH4N(NO2/su
The catalytic chemistry of HCN + NO2 over Na- and Ba-Y,FAU: An in situ FTIR and TPD/TPR study
Szanyi, János,Kwak, Ja Hun,Peden, Charles H. F.
, p. 1481 - 1490 (2005)
The adsorption of HCN and the reaction of HCN with NO2 over Na-, and Ba-Y,FAU zeolite catalysts were investigated using in situ FTIR and TPD/ TPR spectroscopies. Both catalysts adsorb HCN molecularly at room temperature, and the strength of ads
Baiker, A.,Dollenmaier, P.,Reller, A.
, p. 394 - 398 (1987)
Wilkins, C. J.,Soper, F. G.
, (1939)
Efficient conversion of NO2 into N2 and O2 in N2 or into N2O5 in Air by 172-nm Xe 2 excimer lamp at atmospheric pressure
Tsuji, Masaharu,Kawahara, Masashi,Senda, Makoto,Noda, Kenji
, p. 376 - 377 (2007)
Decomposition of NO2 (200 ppm) in N2 or air by 172-nm Xe2 excimer lamp was studied at 1 atm. The NO2 conversion in N2 was 99%, and the formation ratios of N2, O 2, NO, and N2O were 47, 98, 0, and 2%, respectively, after 30 min irradiation. The NO2 in air (5-20% O2) could be completely converted to N2O5 and HNO3 due to reactions by O3 and H2O after only 1.0-1.5 min irradiation. The present results give a new simple photochemical aftertreatment technique of NO2 in air without using any catalysts. Copyright
Mesostructured CeO2 and Pd/CeO2 nanophases: Templated synthesis, crystalline structure and catalytic properties
Zhang,Yang,Shen,Wang
, p. 182 - 190 (2005)
This work reports a ceria solid and Pd/ceria catalyst prepared through a surfactant-templated synthesis route used for simultaneous abasement of NO and CO emissions. The surface features, textural properties and crystalline structure of ceria and Pd/ceria catalyst were studied by means of thermogravimetric analysis (TGA), N2 physisorption isotherms and in situ Fourier transform infrared (FT-IR) spectroscopy, high resolution electron transmission microscopy (TEM) and X-ray diffraction (XRD) techniques. In the calcination procedure, part of the adsorbed water on the surface of the solid was derived into unidentate and bidentate hydroxyls associated with surface cationic ions of ceria. The surfactant cations were strongly interacted with the solid during the preparation, which induces defects formation in the crystalline structure of the annealed ceria. The retained surfactant in the solid could be combusted to yield CO2, water and organic molecules with a small amount of coke-like deposits. The resultant ceria showed mesoporous texture and cubic phase containing lattice defects in the crystalline structure. The Pd/CeO2 catalyst was very active for NO reduction via CO with a high selectivity to N2. A 100% NO conversion with a selectivity to 100% N2 was achieved over the Pd/ceria catalyst at a reaction temperature of 300 °C. The catalytic activity and selectivity of this catalyst are much superior to the catalysts of Pt or Rh supported on TiO2, Al2O3, TiO 2-Al2O3 and ZrO2-Al 2O3 prepared by a sol-gel method. A possible reaction mechanism of NO reduction by CO over the Pd/CeO2 catalyst was discussed.
Effects of O2 on the reduction of NO over prereduced CaO surfaces: A mechanistic understanding
Acke, Filip,Panas, Itai
, p. 2195 - 2201 (1999)
The effect of O2 on the reduction of NO over prereduced CaO surfaces is investigated. The experimental results suggest the existence of at least three different reaction channels, of which two are related to the high-temperature reduction of the CaO surfaces and involve the use of extra electrons in breaking the NO bond. The third reaction channel does not employ extra electrons for bond breaking, but the activity is affected by the amount of adsorbed surface oxygens. The difference between the former two reaction channels is found in the temperature needed for an observable activity. The reaction channel which is already active at low temperatures is described by a model based on F-centers, whereas the one which needs elevated temperatures involves a hole transport through the bulk. The activation energy for this transport is determined experimentally using a temperature-programmed reaction technique as well as theoretically by means of ab initio quantum chemistry calculations. Room-temperature exposure to O2 is suggested to result in a poisoning of the F-centers, but has only a minor effect on the reaction channel proposed for high temperatures. Effects on the reduction of NO of time as well as temperature for the O2 exposure step are also investigated and found to be consistent with an understanding based on the coexistence of different reaction channels. ? 1999 American Chemical Society.
Modified Electronic Structure and Enhanched Catalytic Activity of Cobalt Tetraphenylporphirin Supported by Titanium Dioxide
Mochida, Isao,Tsuji, Kazuhiko,Suetsugu, Katsuya,Fujitsu, Hiroshi,Takeshita, Kenjiro
, p. 3159 - 3162 (1980)
The electronic structure and the catalytic activity of cobalt tetraphenylporphirin supported on titanium dioxide (CoTPP/TiO2) were studied in order to reveal the electronic interaction between the oxide and the planar complex, which can modify the nature of the latter substance.CoTPP/TiO2 showed a sharp isotropic ESR signal at a g value of 2.003 and a UV band around 590 nm, values which were completely different from those of the unsupported CoTTP.The formation of an anionic radical, which has an odd electron in the porphyrin ring, is suggested.CoTTP?TiO2 showed remarkable catalytic activity for the reduction of nitric oxide to nitrous oxide and molecular nitrogen even at 50 deg C with hydrogen, which was found to be adsorbed on CoTTP/TiO2.The activity was much accelerated at 150 deg C, where a successive reduction of nitric oxide in the sequence NO --> N2O --> N2 was clearly indicated.
Catalytic activity of Ir for NO-CO reaction in the presence of SO2 and excess oxygen
Ogura, Masaru,Kawamura, Aya,Matsukata, Masahiko,Kikuchi, Eiichi
, p. 146 - 147 (2000)
Catalytic performance of Ir catalysts for reduction of nitric oxide with carbon monoxide in the presence of SO2 and excess oxygen was investigated. NO was selectively reduced with CO on Ir/silicalite in an oxidizing atmosphere containing 1% to
Selective Reduction of NO by NH3 over Chromia on Titania Catalyst: Investigation and Modeling of the Kinetic Behavior
Willi,Maciejewski,Goebel,Koeppel,Baiker
, p. 356 - 367 (1997)
The kinetics and the parametric sensitivity of the selective catalytic reduction (SCR) of NO by NH3 were investigated over a chromia on titania catalyst. The chromium oxide phase was made up predominantly of X-ray amorphous Cr2O3. High SCR activity and selectivity to N2 was attained at low temperatures. The high selectivity is attributed to the absence of significant amounts of CrO2 and crystalline α-Cr2O3 which favor N2O formation. The selectivity to N2O increased with higher temperature. Addition of up to 6% H2O to the dry feed reduced the rate of NO conversion and decreased the undesired formation of N2O. The effect of water on the catalytic behavior was reversible. In the absence of oxygen, the reaction between NO and NH3 became marginal independently whether H2O was present or not. Small amounts of oxygen were sufficient to restore SCR activity. Admission of SO2 to the SCR feed resulted in a severe loss of activity. The poisoning of the catalyst by SO2 was already notable for low SO2 concentrations (30 ppm) and for temperatures up to 573 K. X-ray photoelectron and FTIR spectroscopy revealed the presence of sulfate species on the catalyst surface. Analysis of the kinetic data indicated that the SCR reaction is first order in NO and zeroth order in NH3 for temperatures in the range 400-520 K. The estimated activation energies for dry and wet feed amounted to 60.0 ± 1.6 kJ/mol (95% confidence limits). For temperatures in the range 400-520 K, and for a SO2 free feed, the steady-state kinetic data could be well described with a model based on an Eley-Rideal type reaction between activated ammonia surface species and gaseous or weakly adsorbed NO.
Reaction of trans-[RuNO(NH3)4(OH)]Cl2 with nitric acid and synthesis of ammine(nitrato)nitrosoruthenium complexes
Kabin,Emel'yanov,Vorob'yev,Alferova,Tkachev,Baidina
, p. 1146 - 1153 (2012)
The reaction of trans-[RuNO(NH3)4(OH)]Cl2 with nitric acid has been studied. Reaction prod- ucts have been identified by IR spectroscopy, NMR, mass spectrometry, powder and single-crystal X-ray dif- fraction, and chemical
TG-FTIR, DSC and ESCA characterization of histamine complexes with transition metal ions
Materazzi,Curini,Gentili,D'Ascenzo
, p. 45 - 50 (1997)
The thermoanalytical study of some MeHmx complexes (Hm = histamine; x = 1, 2) and MeHmx(NO3)2 (x = 2, 4) with Co(II), Ni(II) and Cu(II) is reported. By TG-FTIR coupled analysis,
On the surface steps of a heterogeneous catalytic reaction
Matyshak
, p. 812 - 817 (2007)
Based on a study of the properties of intermediate complexes in the reactions of low-temperature ammonia oxidation and nitrogen oxide reduction in the presence and absence of oxygen on various catalysts, it was hypothesized that the sequence of steps in the formation of reaction products on chemically different catalysts can be the same if the initial adsorption forms of reactants are identical. In this case, variations in catalysts or reaction conditions affect the ratio between reaction rates.
A novel mechanism for poisoning of metal oxide SCR catalysts: Base-acid explanation correlated with redox properties
Chang, Huazhen,Li, Junhua,Su, Wenkang,Shao, Yuankai,Hao, Jiming
, p. 10031 - 10034 (2014)
A novel mechanism is proposed for the poisoning effect of acid gases and N2O formation on SCR catalysts involving base-acid properties correlated with redox ability of M-O or M-OH (M = Ce or V) of metal oxides and the strength of their basicity responsible for resistance to HCl and SO 2 at medium and low temperatures. This journal is the Partner Organisations 2014.
Monitoring of the evolved gases in apatite-ammonium sulfate thermal reactions
Tonsuaadu, Kaia,Pelt,Borissova, Maria
, p. 655 - 658 (2005)
Thermal reactions in natural fluorapatite or fluorcarbonate apatite and ammonium sulfate mixtures with mole ratio 1:4 at calcination up to 500°C were studied by simultaneous thermogravimetry and FTIR analysis of the evolved gases. The composition of natur
Evidence for Homolytic Decomposition of Ammonium Nitrate at High Temperature
Brower, K. R.,Oxley, Jimmie C.,Tewari, Mohan
, p. 4029 - 4033 (1989)
Rates of decomposition of ammonium nitrate in the liquid and vapor state have been measured at temperatures up to 400 deg C.The evidence indicates that an ionic mechanism operating at temperatures below 290 deg C is overtaken by a homolytic mechanism at higher temperatures.The activation energy increases to 193 kJ/mol, which is nearly equal to the N-O bond energy in HNO3.Water and NH3 strogly inhibit the ionic reaction at low temperature, but the effect fades away at high temperature.There is no primary H/D kinetic isotope effect.The reaction rates of liquid and vapor are nearly the same at high temperature.The rate at high temperature is given by (kT/h)e4.06e-23300/T.
Carbon-Nitrogen and Nitrogen-Nitrogen Bond Formation from Nucleophilic Attack at Coordinated Nitrosyls in Fe and Ru Heme Models
Abucayon, Erwin G.,Powell, Douglas R.,Richter-Addo, George B.
, p. 9495 - 9498 (2017)
The conversion of inorganic NOx species to organo-N compounds is an important component of the global N-cycle. Reaction of a C-based nucleophile, namely the phenyl anion, with the ferric heme nitrosyl [(OEP)Fe(NO)(5-MeIm)]+ generates a mixture of the C-nitroso derivative (OEP)Fe(PhNO)(5-MeIm) and (OEP)Fe(Ph). The related reaction with [(OEP)Ru(NO)(5-MeIm)]+ generates the (OEP)Ru(PhNO)(5-MeIm) product. Reactions with the N-based nucleophile diethylamide results in the formation of free diethylnitrosamine, whereas the reaction with azide results in N2O formation; these products derive from attack of the nucleophiles on the bound NO groups. These results provide the first demonstrations of C-N and N-N bond formation from attack of C-based and N-based nucleophiles on synthetic ferric-NO hemes.
Thermal behaviour of ammonium nitrate prills coated with limestone and dolomite powder
Rudjak,Kaljuvee,Trikkel,Mikli
, p. 749 - 754 (2010)
The thermal behaviour of ammonium nitrate (AN) and its prills coated with limestone and dolomite powder was studied on the basis of commercial fertilizer-grade AN and six Estonian limestone and dolomite samples. Coating of AN prills was carried out on a plate granulator and a saturated solution of AN was used as a binding agent. The mass of AN prills and coating material was calculated based on the mole ratio of AN/(CaO + MgO) = 2:1. Thermal behaviour of AN and its coated prills was studied using combined TG-DTA-FTIR equipment. The experiments were carried out under dynamic heating conditions up to 900 °C at the heating rate of 10 °C min-1 and for calculation of kinetic parameters, additionally, at 2, 5 and 20 °C min-1 in a stream of dry air. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The results of TG-DTA-FTIR analyses and the variation of the value of activation energy E along the reaction progress α indicate the complex character of the decomposition of neat AN as well as of the interactions occurring at thermal treatment of AN prills coated with limestone and dolomite powder.
Characterization and catalytic activity for the NO decomposition and reduction by CO of nanosized Co3O4
Zhang, Zhaoliang,Geng, Haoran,Zheng, Lisheng,Du, Bin
, p. 317 - 321 (2005)
Nanosized Co3O4 prepared by a precipitation method was characterized by TEM, XRD, BET and TPD techniques, and studied for NO decomposition and reduction by CO. It is found that Co3O4 thus obtained has a specific surface area of 23.4 m2/g and an average particle size of 26 nm. Catalytic tests showed that full NO conversion to N2 was obtained above 300 °C. A redox mechanism between Co 3+ and Co2+ ions based on NO decomposition is proposed.
SURFACE STATES OF MoO3 ON ZrO2 AND CATALYTIC PROPERTIES FOR THE REACTION OF NO WITH H2
Iizuka, Tokio,Itoh, Masahumi,Hattori, Hideshi,Tanabe, Kozo
, p. 501 - 508 (1982)
The adsorption and reaction of nitric oxide on reduced molybdena-zirconia were studied by means of e.s.r., i.r. and u.v. spectroscopies.On the surface, at least two types of nitrosyl complex exist.At an early stage of reduction, a diamagnetic dinitrosyl complex with i.r. bands at ca. 1790 and 1690 cm-1 formed on NO adsorption and was ascribed to Mo(4+)(NO)2.After reduction at a higher temperature, a paramagnetic dinitrosyl species appeared upon NO adsorption and was tentatively assigned to Mo(5+)(NO)2.Nitric oxide can adsorb on Mo(5+) in tetrahedral coordination, but not on Mo(5+) in octahedral coordination.This can be explained by the coordination being limited.For the reaction of NO with H2, the species of Mo(5+)(NO)2 was concluded to be a main active complex in the catalytic cycle.
Solid-gas reactions for nitroxyl (HNO) generation in the gas phase
Carrone, Guillermo,Mazzeo, Agostina,Marceca, Ernesto,Pellegrino, Juan,Suárez, Sebastián,Zarenkiewicz, Jessica,Toscano, John P.,Doctorovich, Fabio
, (2021/07/25)
We present a novel nitroxyl (HNO) generation method, which avoids the need of using a liquid system or extreme experimental conditions. This method consists of the reaction between a gaseous base and an HNO donor (Piloty's acid) in the solid phase, allowi
The Effects of Platinum Dispersion and Pt State on Catalytic Properties of Pt/Al2O3 in NH3 Oxidation
Slavinskaya, Elena M.,Kibis, Lidiya S.,Stonkus, Olga A.,Svintsitskiy, Dmitry A.,Stadnichenko, Andrei I.,Fedorova, Elizaveta A.,Romanenko, Anatolii V.,Marchuk, Vasyl,Doronkin, Dmitry E.,Boronin, Andrei I.
, p. 313 - 327 (2020/10/30)
Dependence of NH3 oxidation on the state and dispersion of Pt species in Pt/γ-Al2O3 catalysts was investigated. Prereduced Pt/γ-Al2O3 catalysts containing Pt0 nanoparticles exhibited significantly higher activity than preoxidized ones with the same Pt dispersion. The most significant improvement of the catalytic activity (TOF increased by 30 times) was observed when the size of Pt0 particles increased from ~1 to ~8 nm. N2 selectivity was found to be mainly determined by the reaction temperature, with a minor influence of Pt particle size. Preoxidized catalysts containing ionic Pt were activated by the reaction medium, while partial deactivation was observed for the prereduced ones. The activity improvement was associated with the presence of Pt4+/Pt2+ species on the surface of preoxidized catalysts. The activity decrease of the prereduced catalysts was due to the partial oxidation and subsequent redispersion of Pt particles. Introduction of H2O and CO2 to the reaction mixture only moderately influenced NH3 oxidation activity shifting NH3 conversion curves by about +15 °C.
Short-lived intermediate in N2O generation by P450 NO reductase captured by time-resolved IR spectroscopy and XFEL crystallography
Nomura, Takashi,Kimura, Tetsunari,Kanematsu, Yusuke,Yamada, Daichi,Yamashita, Keitaro,Hirata, Kunio,Ueno, Go,Murakami, Hironori,Hisano, Tamao,Yamagiwa, Raika,Takeda, Hanae,Gopalasingam, Chai,Kousaka, Ryota,Yanagisawa, Sachiko,Shoji, Osami,Kumasaka, Takashi,Yamamoto, Masaki,Takano, Yu,Sugimoto, Hiroshi,Tosha, Takehiko,Kubo, Minoru,Shiro, Yoshitsugu
, (2021/05/28)
Nitric oxide (NO) reductase from the fungus Fusarium oxysporum is a P450-type enzyme (P450nor) that catalyzes the reduction of NO to nitrous oxide (N2O) in the global nitrogen cycle. In this enzymatic reaction, the heme-bound NO is activated by the direct hydride transfer from NADH to generate a short-lived intermediate (I), a key state to promote N–N bond formation and N–O bond cleavage. This study applied time-resolved (TR) techniques in conjunction with photolabile-caged NO to gain direct experimental results for the characterization of the coordination and electronic structures of I. TR freeze-trap crystallography using an X-ray free electron laser (XFEL) reveals highly bent Fe–NO coordination in I, with an elongated Fe–NO bond length (Fe–NO = 1.91 ?, Fe–N–O = 138°) in the absence of NAD+. TR-infrared (IR) spectroscopy detects the formation of I with an N–O stretching frequency of 1,290 cm?1 upon hydride transfer from NADH to the Fe3+–NO enzyme via the dissociation of NAD+ from a transient state, with an N–O stretching of 1,330 cm?1 and a lifetime of ca. 16 ms. Quantum mechanics/ molecular mechanics calculations, based on these crystallographic and IR spectroscopic results, demonstrate that the electronic structure of I is characterized by a singly protonated Fe3+–NHO?? radical. The current findings provide conclusive evidence for the N2O generation mechanism via a radical–radical coupling of the heme nitroxyl complex with the second NO molecule.