Kinetics and mechanism of the C2H5O2 + NO reaction: A temperature and pressure dependence study using chemical ionization mass spectrometry

The overall rate coefficient (k₁) for the reaction of C₂H₅O₂ + NO has been measured using the turbulent flow CIMS technique. The temperature dependence of the rate coefficient was investigated between 203 and 298 K. Across the temperature range, the experimentally determined rate coefficients showed good agreement with previous studies and were fitted using an Arrhenius type analysis to yield the expression k₁ = (1.75) × 10^?12 exp[(462 ± 19)/T] cm³ molecule^?1 s^?1. Experiments were carried out in the pressure range of 100–200 Torr within the stated temperature range, where the rate coefficients were shown to be invariant with pressure. The branching ratio of the reaction was also assessed as a function of temperature and was found to proceed 100 ± 5% via the C₂H₅O + NO₂ reactive channel. This work represents the first temperature and pressure study over which the branching ratio has been studied. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 253–260, 2005     

Kinetics and branching ratio studies of the reaction of C2H5O2 + HO2 using chemical ionisation mass spectrometry

The overall rate coefficient for the reaction of C(2)H(5)O(2) with HO(2) was determined using a turbulent flow chemical ionization mass spectrometer (TF-CIMS) system over the pressure range of 75 to 200 Torr and temperatures between 195 and 298 K. The temperature dependence of the overall rate coefficient for the reaction between C(2)H(5)O(2) and HO(2) was fitted using the following Arrhenius expression: k(T) = (2.08) x 10(-13) exp [(864 +/- 79)/T] cm(-3) molecule(-1) s(-1). The upper limits for the branching ratios for reactive channels leading to O(3) and OH production were quantified for the first time. A tropospheric model has been used to assess the impact of the experimental error of the rate coefficients determined in this study on predicted concentrations of a number of key species, including O(3), OH, HO(2), NO and NO(2). In all cases it is found that the propagated error is very small and will not in itself be a major cause of uncertainty in modelled concentrations. However, at low temperatures, where there is a wide discrepancy between existing kinetic studies, modelling using the range of kinetic data in the literature shows a small but significant variation for [C(2)H(5)O(2)], [C(2)H(5)OOH], [NO(x)] and the HO(2) : OH ratio. Furthermore, a structure-activity relationship (SAR) was developed to rationalise the reactivity of the reaction between RO(2) and HO(2).     

Kinetics of the reaction C2H5 + HO2 by time-resolved mass spectrometry

The overall rate constant for the radical-radical reaction C2H5 + HO2 --> products has been determined at room temperature by means of time-resolved mass spectrometry using a laser photolysis/flow reactor combination. Excimer laser photolysis of gas mixtures containing ethane, hydrogen peroxide, and oxalyl chloride was employed to generate controlled concentrations of C2H5 and HO2 radicals by the fast H abstraction reactions of the primary radicals Cl and OH with C2H6 and H2O2, respectively. By careful adjustments of the radical precursor concentrations, the title reaction could be measured under almost pseudo-first-order conditions with the concentration of HO2 in large excess over that of C2H5. From detailed numerical simulations of the measured concentration-time profiles of C2H5 and HO2, the overall rate constant for the reaction was found to be k1(293 K) = (3.1 +/- 1.0) x 10(13) cm3 mol(-1) s(-1). C2H5O could be confirmed as a direct reaction product.     

Investigation of the rate coefficient for O(3p) + NO2 → O2 + NO

Measurements of the rate coefficient of the reaction (O³P) + NO₂ → O₂ + NO have been made at 296°K and 240°K, using the technique of NO₂* chemiluminescent decay. Values of 9.3 × 10^?12 cm³ molec^?1 sec^?1 at 296°K and 10.5 × 10^?12 cm³ molec^?1 sec^?1 at 240°K were obtained, in excellent agreement with the recent results of Davis, Herron, and Huie [1]. The earlier lower values may have resulted from loss of NO₂ on surfaces.     

Differentiation of isobaric compounds using chemical ionization reaction mass spectrometry

The technique of proton transfer reaction mass spectrometry (PTR-MS) couples a proton transfer reagent, usually H3O+, with a drift tube and mass spectrometer to determine concentrations of volatile organic compounds. Here we describe a first attempt to use chemical ionization (CI) reagents other than proton transfer species inside a PTR-MS instrument. The ability to switch to other types of CI reagents provides an extra dimension to the technique. This capability is demonstrated by focusing on the ability to distinguish several isobaric aldehydes and ketones, including the atmospherically important molecules methacrolein and methyl vinyl ketone. Two CI reagents were selected, H3O+ and NO+, both being cleanly generated in a low intensity radioactive source prior to injection into the drift tube. By recording spectra with both of these reagents, the contributions from different isobaric molecules can be separated by virtue of their unique spectrometric 'fingerprints'. The work demonstrates that this form of instrumentation is not restricted to proton transfer reagents and is the basis of a more general technique, chemical ionization reaction mass spectrometry (CIRMS).     

Kinetics of the CH3O2 + HO2 reaction: A temperature and pressure dependence study using chemical ionization mass spectrometry

A temperature and pressure kinetic study for the CH₃O₂ + HO₂ reaction has been performed using the turbulent flow technique with a chemical ionization mass spectrometry detection system. An Arrhenius expression was obtained for the overall rate coefficient of CH₃O₂ + HO₂ reaction: k(T) = (3.82^+2.79_?1.61) × 10^?13 exp[(?781 ± 127)/T] cm^?3 molecule^?1 s^?1. A direct quantification of the branching ratios for the O₃ and OH product channels, at pressures between 75 and 200 Torr and temperatures between 298 and 205 K, was also investigated. The atmospheric implications of considering the upper limit rate coefficients for the O₃ and OH branching channels are observed with a significant reduction of the concentration of CH₃OOH, which leads to a lower amount of methyl peroxy radical. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 571–579, 2007     

Characterization of cyclotrimethylenetrinitramine (RDX) by pyrolysis H2O/D2O atmospheric-pressure chemical ionization tandem mass spectrometry

The oxidative pyrolysis-atmospheric-pressure chemical ionization tandem mass Spectrometry (Py-APCI MS/MS) of Cyclotrimethylenetrinitramine (RDX) was investigated under various sample introduction conditions. Subambient (0.97 atm) as opposed to ambient (0.98 atm) pressure (1 atm = 101325 kPa) facilitated the appearance of new pyrolysis mass spectral ions, including m/z 44. Deuterated decomposition products from [²H]RDX contained amide groups and, depending on the ion source pressure, significant differences in the degree of proton-deuterium exchange occurred on the amide groups. The D₂O Py-APCI MS/MS method also confirmed and extended the analogous H₂O APCI information from RDX, [²H]RDX and pure standards. The m/z 44 decompositon species was identified as protonated dimethylimine, [H₃CN?CH₂]⁺ as opposed to its primary amine isomer, [H₃CC(H)?NH]H⁺, which contains an acidic proton. It was determined that m/z 60 is due to protonated N-methylformamide and acetaldoxime, [H₃CC(H)?NOH]H⁺.     

The importance of NO+ (H2O)4 in the conversion of NO+ (H2O)n to H3O+ (H2O)n: I. Kinetics measurements and statistical rate modeling

The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of NO(+)(H(2)O)(3), the present results show that NO(+)(H(2)O)(4) plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H(2)O to NO(+)(H(2)O)(1-3) and the reactions of NO(+)(H(2)O)(3,4) with H(2)O to form H(3)O(+)(H(2)O)(2,3), respectively. In addition, thermal dissociation of NO(+)(H(2)O)(4) to lose HNO(2) was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that NO(+)(H(2)O)(4) accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association.     

Computational study on the mechanism and rate constant for the C6H5 + C6H5NO reaction

The reaction mechanism of C6H5 + C6H5NO involving four product channels on the doublet-state potential energy surface has been studied at the B3LYP/6-31+G(d, p) level of theory. The first reaction channel occurs by barrierless association forming (C6H5)2NO (biphenyl nitroxide), which can undergo isomerization and decomposition. The second channel takes place by substitution reaction producing C12H10 (biphenyl) and NO. The third and fourth channels involve direct hydrogen abstraction reactions producing C6H4NO + C6H6 and C6H5NOH + C6H4, respectively. Bimolecular rate constants of the above four product channels have been calculated in the temperature range 300-2000 K by the microcanonical Rice-Ramsperger-Kassel-Marcus theory and/or variational transition-state theory. The result shows the dominant reactions are channel 1 at lower temperatures (T < 800 K) and channel 3 at higher temperatures (T > 800 K). The total rate constant at 7 Torr He is predicted to be k(t) = 3.94 x 10(21) T(-3.09) exp(-699/T) for 300-500 K, 2.09 x 10(20) T(-3.56) exp(2315/T) for 500-1000 K, and 1.51 x 10(2) T(3.30) exp(-3043/T) for 1000-2000 K (in units of cm3 mol(-1) s(-1)), agreeing reasonably with the experimental data within their reported errors. The heats of formation of key products including biphenyl nitroxide, hydroxyl phenyl amino radical, and N-hydroxyl carbazole have been estimated.     

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.     

Direct chemical ionization mass spectrometry of short-chain polysaccharides.

Underivatized short-chain polysaccharides such as two inulins from different plants containing up to 35-40 monosaccharide units with molecular weights of up to 6500 Da and dextran T 1.5 containing up to 16-20 monosaccharide units with molecular weights of up to 3200 Da have been investigated by direct chemical ionization. Under soft ionization conditions such as ammonia chemical ionization and reduced ion-source temperature, it was possible to obtain spectra of the native polysaccharides showing dominant ion series corresponding to ammonia adduct ions of oligosaccharides, and also ion series corresponding to ammonia adduct ions of anhydro-oligosaccharides.     

Kinetics of the reaction of C2H5O2 with NO at 295 K

The reaction of C₂H₅O₂ with NO in helium carrier gas at 295 K with [He] = 1.6 × 10¹⁷ cm^?3 has been studied using a gas flow reactor sampled by a mass spectrometer. Because no parent molecular ion or suitable fragment ion produced by C₂H₅O₂ could be detected, the reaction was followed by measuring the formation of NO₂. In so doing, account had to be taken of the small amount of HO₂ known to be present in the reaction mixture, which also leads to NO₂ on reaction with NO. The rate coefficient for the total reaction of C₂H₅O₂ with NO was found to be (8.9 ± 3.0) × 10^?12 cm³/s, and the path which produces NO₂ was found to account for at least 80% of all C₂H₅O₂.     

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.     

(C26H40N2O4)[Ln(NO3)5H2O]的合成及其铕缔合物的晶体结构

合成了4个新型的稀土化合物(C₂₆H₄₀N₂O₄)[Ln(NO₃)₅H₂O](Ln=Pr,Nd,Sm,Eu),采用元素分析和红外光谱表征,用四圆衍射仪测定了其中(C₂₆H₄₀N₂O₄)[Eu(NO₃)₅H₂O]的晶体结构,属三斜晶系,P1空间群,晶胞参数:α=0.9100(4)nm,b=1.3560(3)nm,c=1.6463(4)nm;α=68.62(2)°,β=74.84(3)°,γ=87.50(2)°;Z=2.中心铕离子由5个硝酸根的10个氧原子和1个水分子中的氧原子配位,配位数是11.1,7,10,16-四氧-4,13-二氮杂-N,N'-二苄基环十八烷(N,N'-二苄基穴醚(2,2))未参与配位.     

Direct ab initio dynamics calculations on the rate constants for the hydrogen-abstraction reaction of C2H5F with O (3P)

The hydrogen-abstraction reaction C₂H₅F+O → C₂H₄F+OH has been studied by a dual-level direct dynamics method. For the reaction, three reaction channels, one for α-abstraction and two for β-abstraction, have been identified. The potential-energy surface information is obtained at the MP2(full)/6-311G(d,p) and PMP2(full)/6-311G(3df,3pd) (single-point) levels. By canonical variational transition-state theory, rate constants for each reaction channel are calculated with a small-curvature tunneling correction. The total rate constant is calculated from the sum of the individual rate constants and the temperature dependence of the branching ratios is obtained over a wide range of temperatures from 300 to 5,000 K. The agreement of the rate constants with experiment is good in the experimental temperature range from 1,000 to 1,250 K. The calculated results indicate that at low temperatures α-abstraction is most likely to be the major reaction channel, while β-abstraction channels will significantly contribute to the whole reaction rate as the temperature increases. Received: 23 January 2002 / Accepted: 23 June 2002 / Published online: 20 September 2002     

Direct analysis of biological samples using extractive electrospray ionization mass spectrometry (EESI-MS)

Mass spectrometry (MS) is one of the most widely used techniques for the analysis of biological samples. In the past decade, a novel improvement in MS was the invention of ambient ionization which stands out owing to its unique capability of direct analysis of complex samples with no or minimal pretreatment. In this review, extractive electrospray ionization (EESI), a representative ambient ionization technique, is introduced focusing on its mechanism, instrumentation, and applications in biological analysis. EESI uses a traditional ESI channel to produce primary ions which subsequently ionize neutral chemicals from the sample introduction channel through an online extraction process. When analyzing biological samples, EESI has advantages of rapid analysis, high matrix tolerance, and the ability to perform in vivo analysis. According to previous studies, EESI is able to directly analyze various chemicals in complex biological specimens in liquid, gas, and solid states. EESI can provide a sensitive and selective measurement of biological samples for both qualitative and quantitative purposes. Therefore, it is anticipated that EESI will have promising applications, especially in fields which require the fast and/or in vivo analysis of biological samples with complicated matrixes.     

Theoretical reinvestigation of the O(3P) + C6H6 reaction: quantum chemical and statistical rate calculations

The lowest-lying triplet and singlet potential energy surfaces for the O(3P) + C6H6 reaction were theoretically characterized using the "complete basis set" CBS-QB3 model chemistry. The primary product distributions for the multistate multiwell reactions on the individual surfaces were then determined by RRKM statistical rate theory and weak-collision master equation analysis using the exact stochastic simulation method. It is newly found that electrophilic O-addition onto a carbon atom in benzene can occur in parallel on two triplet surfaces, 3A' and 3A' '; the results predict O-addition to be dominant up to combustion temperatures. Major expected end-products of the addition routes include phenoxy radical + H*, phenol and/or benzene oxide/oxepin, in agreement with the experimental evidence. While c-C6H5O* + H* are nearly exclusively formed via a spin-conservation mechanism on the lowest-lying triplet surface, phenol and/or benzene oxide/oxepin are mainly generated from the lowest-lying singlet surface after inter-system crossing from the initial triplet surface. CO + c-C5H6 are predicted to be minor products in flame conditions, with a yield < or = 5%. The O + C6H6 --> c-C5H5* + *CHO channel is found to be unimportant under all relevant combustion conditions, in contrast with previous theoretical conclusions (J. Phys. Chem. A 2001, 105, 4316). Efficient H-abstraction pathways are newly identified, occurring on two different electronic state surfaces, 3B1 and 3B2, resulting in hydroxyl plus phenyl radicals; they are predicted to play an important role at higher temperatures in hydrocarbon combustion, with estimated contributions of ca. 50% at 2000 K. The overall thermal rate coefficient k(O + C6H6) at 300-800 K was computed using multistate transition state theory: k(T) = 3.7 x 10-16 x T 1.66 x exp(-1830 K/T) cm(3) molecule(-1) s(-1), in good agreement with the experimental data available.     

Direct ab initio dynamics study on the rate constants and kinetics isotope effects of CH(3)O+H-->CH(2)O+H(2) reaction

We present a direct ab initio dynamics study of thermal rate constants of the hydrogen abstraction reaction of CH(3)O+H-->CH(2)O+H(2). The unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional with Dunning's correlation consistent polarized valence double-zeta basis set, the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set, and the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set methods were employed to optimize the structures and to calculate frequencies for all stationary points. Minimum energy paths were obtained by the unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional and the unrestricted quadratic configuration interaction calculation including single and double substitutions with the same Dunning's correlation consistent polarized valence double-zeta basis set levels of theory. No barrier is found at the unrestricted Becke's half-and-half hybrid functional using the Lee-Yang-Parr correlation functional with Dunning's correlation consistent polarized valence double-zeta basis set level of theory in contrast to a small barrier of 1.43 kcal mol(-1) at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set level of theory. In particular, the barrier vanishes as the energies along the minimum energy path MEP are refined at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set level of theory. Smaller barriers of 0.47 and 0.17 kcal mol(-1) were obtained at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set and the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set based on the geometries at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence triple-zeta basis set levels of theory, respectively. The forward rate constants are evaluated with the canonical variational transition state theory in the temperature range of 300-2500 K. The calculated forward rate constants at the unrestricted quadratic configuration interaction calculation including single and double substitutions with a triples contribution with Dunning's correlation consistent polarized valence triple-zeta basis set based on the geometries at the unrestricted quadratic configuration interaction calculation including single and double substitutions with Dunning's correlation consistent polarized valence double-zeta basis set level of theory are in good agreement with the available experimental data. The kinetic isotope effects are estimated.     

A study of the reaction NO3 + NO2 + M → N2O5 + M(M = N2, O2)

The gas-phase reaction of the NO₃ radical with NO₂ was investigated, using a flash photolysis-visible absorption technique, over the total pressure range 25–400 Torr of nitrogen or oxygen diluent at 298 ± 2 K. The absolute rate constants determined (in units of 10^?13 cm³ molecule^?1 s^?1) at 25, 100, and 400 Torr total pressure were, respectively, (4.0 ± 0.5), (7.0 ± 0.7), and (10 ± 2) for M = N₂ and (4.5 ± 0.5), (8.0 ± 0.4), and (8.8 ± 2.0) for M = O₂. These data show that the third-body efficiencies of N₂ and O₂ are identical, within the error limits, and that previous evaluations for M = N₂ are applicable to the atmosphere. In addition, upper limits were determined for the rate constants of the reactions of the NO₃ radical with methanol, ethanol, and propan-2-ol of ?6 × 10^?16, ?9 × 10^?16, and ?2.3 × 10^?15 cm³ molecule^?1 s^?1, respectively, at 298 ± 2 K.