https://backend.orbit.dtu.dk/ws/files/145750384/Nreview_revised.pdf

Modeling nitrogen chemistry in combustion

Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first‐order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a...

Reactions of N( 4 S) atoms with NO and H 2

A tandem hybrid gas cleanup system, consisting of a BaTiO/sub 3/ packed-bed plasma reactor and a CaCO/sub 3/ adsorbent filter, was used to study the removal of NF/sub 3/ from semiconductor-process flue gases. Plasma-chemical kinetics of N/sub 2/-NF/sub 3/-O/sub 2/-H/sub 2/ gas mixtures suggested byproducts observed in the experiments. The laboratory-scale system showed NF/sub 3/ removal at atmospheric pressure. Typically, 100% NF/sub 3/ abatement was achieved with an inlet concentration of 5000 ppm and a gas residence time in the reactor less than 10 s.

Removal of NF/sub 3/ from semiconductor-process flue gases by tandem packed-bed plasma and adsorbent hybrid systems

Experiments on the thermal decomposition of N2O have been carried out in reflected shock waves using the atomic resonance absorption spectrometric (ARAS) technique for monitoring the product O atoms. The results provide a calibration for the ARAS system as well as values for the decomposition rate constant, k1, between 1540 and 2500 K. The present results can be represented as k1=5.25×10−10 exp(−27 921 K/T) cm3 molecule−1 s−1. Additionally, rate constants for the reaction, (2) N+NO→N2+O, have been measured by the laser photolysis‐shock tube (LP‐ST) technique between 1251 and 3152 K. NO serves as both the photolytic source of N(4S) atoms and the reactant molecule. N atoms are monitored by the ARAS method. The results do not show significant temperature dependence and can be represented by k2=(3.7±0.8)×10−11 cm3 molecule−1 s−1 over the experimental temperature range. Values for the reaction, (−2) O+N2→NO+N, can be derived from these results. The results are compared with earlier studies and are then theoret...

Rate constants for the N2O reaction system: Thermal decomposition of N2O; N+NO→N2+O; and implications for O+N2→NO+N

The discharge flow technique has been used with resonance fluorescence detection of N atoms to study the fast radical-radical reaction of ground state nitrogen atoms (^4S_(3/2)) with NO and NO_2. The rate constants obtained are (in units of cm^3 molecule^(−1) s^(−1)) k_1 = (2.2±0.2) × 10^(−11) exp[(160±50)/T] in the temperature range 213 K ≤ T ≤ 369 K for N + NO → N_2 + O and k_2 = (5.8±0.5) × 10^(−12) exp [(220±50)/T] in the temperature range 223 K ≤ T ≤ 366 K for N + NO_2 → N_2O + O. The reported error limits are at the 95% confidence level. The reaction kinetics are consistent with other radical-radical reactions, essentially no enthalpic barrier is observed. Substitution of the measured rate of R_1 for the value recommended hi the latest Jet Propulsion Laboratory compendium [DeMore et al., 1992] results in a small change in the concentration of ozone predicted in a two-dimensional photochemical model. Modeled ozone concentrations are higher (approximately 1%) in the high-latitude upper stratosphere as a result of a 3–10% reduction in the calculated concentrations of NO_y.

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Kinetics of reactions of ground state nitrogen atoms (4S3/2) with NO and NO2

The kinetics of reactions (at 298 K) involving ground-state N 4S and excited-state N 2D, 2P atoms have been studied using resonance-fluorescence detection in a discharge-flow system. The N 4S+ NO reaction has been studied as a reference reaction: N 4S+ NO [graphic omitted] N2+ O; k1=(3.4 ± 0.3)× 10–11 cm3 molecule–1 s–1(1σ). Also, the rate constant k2 for the N 4S+ NF2 reaction has been determined: N 4S+ NF2 [graphic omitted] 2 NF; k2=(4.6 ± 0.3)× 10–12 cm3 molecule–1 s–1(1σ). The reaction H 2S+ NF2 gives NF radicals in the a1Δ state with a branching ratio 0.9: H 2S+ NF2→ NF a1Δ+ HF X1∑+. This conclusion is drawn from a study of concentration profiles of N 4S and N 2D atoms in the state-selective reactions (4a), (4b): H 2S+ NF a1Δ→ N 2D+ HF X1∑+(4a), H 2S+ NF X3∑–→ N 4S+ HF X1∑+.(4b)., Although N 2D atoms are an initial product of the H + NF reaction. N 4S atoms are formed only at longer reaction times when [N 2D] has mostly decayed. Thus, it is inferred that NF X3∑– is not a major initial product of the H + NF2 reaction.Chemiluminescence is emitted in the H + NF2 reaction from excited NF a1Δ, b1∑+ and from excited N2B3Πg and N2a1Πg in the First Positive (B–A) and Lyman–Birge–Hopfield (a–X) band systems. The precursor of NH chemiluminescence in the H + NF2 system is thought to be ground-state NH X3∑– formed in the reaction N 2D+ H2→ NH X3∑–+ H.

Reactions forming electronically-excited free radicals. Part 2.—Formation of N4S, N 2D and N 2P atoms in the H + NF2 reaction, and N atom reactions

Atomic resonance absorption in the far vacuum ultraviolet and atomic resonance fluorescence have been used to investigate the kinetics of primary and secondary processes in the overall reaction of H 2S atoms with NF2 radicals from 298 to 550 K. Rate constants for the following elementary reactions have been determined directly [k298/cm3 molecule–1 s–1(1 σ)]: H + NF2 [graphic omitted] HF + NF; k1=(1.5 ± 0.2)× 10–11; O + NF2 [graphic omitted] NF + FO; k5=(1.8 ± 0.9)× 10–12; N + NF2 [graphic omitted] NF + NF; k8=(3.0 ± 1.2)× 10–12.The overall H + NF2 reactive system, containing H2, is characterised as a self-propagating chain reaction, in which the chain carriers are H, NF and F. Ground-state N 4S atoms are formed by the reaction H + NF, although these atoms play only a minor role in propagating the overall H + NF2 chain reaction. Computer modelling of the H and N atom profiles was used to obtain values for k4 and k2: H + NF [graphic omitted] HF + N; k4=(2.5 ± 0.5)× 10–13; NF + NF [graphic omitted] N2+ 2F; k2=(7.0 ± 3.5)× 10–11. Thus, the predominant decay channel for NF radicals is through rapid bimolecular disproportionation to give N2+ 2F.

Reactions forming electronically-excited free radicals. Part 1.—Ground-state reactions involving NF2 and NF radicals

Reactions forming electronically excited free radicals III: Formation of excited molecular states in the H + NF2 reaction

Metastable singlet NCl radicals are generated in a discharge—flow system efficiently (25 %) by the reaction of Cl atoms and N3 radicals: Cl(2P)+ N3(X2Πg)→ NCl(b1∑+, a1Δ, X3∑–)+ N2(X1∑g+). (1), Singlet NCl reacts with Cl2 to form NCl2 radicals, NCl*+ Cl2→ NCl2+ Cl. NCl2 radicals were detected using mass spectrometry. The NCl(a1Δ) state is the dominant precursor to NCl2. Electronic energy transfer between NCl* and O2 is shown to occur, generating singlet O2.

Chew Toong Cheah

Papers

Reactions forming electronically-excited free radicals. Part 2.—Formation of N4S, N 2D and N 2P atoms in the H + NF2 reaction, and N atom reactions

Reactions forming electronically-excited free radicals. Part 1.—Ground-state reactions involving NF2 and NF radicals

Reactions forming electronically excited free radicals III: Formation of excited molecular states in the H + NF2 reaction

Kinetics of metastable singlet NCl radicals