Termolecular Reaction Research Articles

Reaction kinetics of carbon dioxide with 2-amino-2-hydroxymethyl-1,3-propanediol in aqueous solution obtained from the stopped flow method

Carbon dioxide (CO_2) capture has attracted great interest these days due to the role of CO_2 in global warming and its effects in industrial processes. Thus, higher energy efficient and affordable technologies are required for its removal so as to address these problems. In this work, the reaction kinetics of CO_2 with 2-amino-2-hyroxymethyl- 1,3-propanediol (AHPD), a sterically hindered amine (SHA), was studied by direct stopped flow method. The aim was to research CO_2 absorbent with better CO_2 absorption capacity and reaction kinetics than the commonly applied amine solvents. The study was carried out at 288, 298, and 303 K in a concentration range of 0.5-2.0 kmol/m^3 of AHPD. Based on the pseudo-first-order for the reaction of CO_2, it was found that the reaction can be modeled by a single termolecular reaction mechanism. The reaction rate between CO_2 and aqueous solution of AHPD was 9.99, 12.03, and 16.05 m^3/kmol.s at 288, 298, and 303 K, respectively, while its activation energy was 31.59 kJ/mol. The results obtained were compared with published reaction rate data of other amines. The present study shows that AHPD is a potential SHA as CO_2 absorbent if the reaction rate is enhanced by an additional amine.

Gold Makes the Termolecular Assembly Possible: Surface-Catalyzed Conversion of an Aldehyde to Its Cyclic Trimer

Propanal (C2H5CHO) trimerizes to 2,4,6-triethyl-1,3,5-trioxane ring on the (110) face of gold in vacuo. The three-component coupling is not only selective about which crystal plane to react upon but also metal-dependent. Low-coordinated sites, surface-specific morphology, and electronic properties of gold act in concert to construct the cyclic C–O–C linkages. Interplay between metal coordination and molecule–surface and molecule–molecule interactions help gather the reaction components and preorganize them on the surface, promoting an otherwise termolecular reaction to a unimolecular (intracomplex) one and making the cyclization possible.

Density Functional Theory Study on Carbon Dioxide Absorption into Aqueous Solutions of 2-Amino-2-methyl-1-propanol Using a Continuum Solvation Model

We used density functional theory (DFT) calculations with the latest continuum solvation model (SMD/IEF-PCM) to determine the mechanism of CO(2) absorption into aqueous solutions of 2-amino-2-methyl-1-propanol (AMP). Possible absorption process reactions were investigated by transition-state optimization and intrinsic reaction coordinate (IRC) calculations in the aqueous solution at the SMD/IEF-PCM/B3LYP/6-31G(d) and SMD/IEF-PCM/B3LYP/6-311++G(d,p) levels of theory to determine the absorption pathways. We show that the carbamate anion forms by a two-step reaction via a zwitterion intermediate, and this occurs faster than the formation of the bicarbonate anion. However, we also predict that the carbamate readily decomposes by a reverse reaction rather than by hydrolysis. As a result, the final product is dominated by the thermodynamically stable bicarbonate anion that forms from AMP, H(2)O, and CO(2) in a single-step termolecular reaction.

The kinetics of carbon dioxide capture by solutions of piperazine and N-methyl piperazine

In this paper, kinetics and mechanism of the reaction between CO 2 and piperazine (PZ) or n-methyl piperazine (NMP) in aqueous and alcoholic solutions were investigated using direct stopped-flow technique under a range of temperatures (278, 288 and 298 K). The results show that the reactions follow a single termolecular reaction mechanism and the reaction rate between CO 2 and aqueous PZ (2669(278K), 11335(288K), 18042(298K) m3/kmol⋅s) is significantly higher than that of commonly employed amines, such as monoethanolamine (MEA). Our results strongly suggest that PZ and PZ derivatives can be used as promoters for CO 2 capture by sterically hindered amine solutions.

Experimental Evidence for the Pressure Dependence of the Reaction Rate Constant between Acetic Acid and Hydroxyl Radicals

The reaction rate constant of acetic acid with the hydroxyl radical is measured at 93 Torr with our high-pressure flow system (HPFS) and found to display a negative temperature dependence that can be described by the Arrhenius expression, k(T) = (2.44 ± 0.22) × 10(-14) exp ((1027 ± 24)/T)) cm(3) molecule(-1) s(-1). Compared with our previously reported 7 Torr data, we find a noticeable pressure dependence. This dependence is observed to increase with decreasing temperature. This finding is consistent with a termolecular reaction mechanism. It is the first experimental evidence of the pressure dependence for this rate constant. A kinetics model is constructed, and the model results agree qualitatively with our experimental data. The extrapolated rate constant of the title reaction would be faster than previously believed at conditions of the upper troposphere/lower stratosphere, suggesting that the importance of acetic acid in its impact on HO(x) chemistry is currently underestimated.

Termolecular Kinetic Model for CO2‐Alkanolamine Reactions: An Overview

AbstractThe CO2 reaction with alkanolamines has received considerable attention by both academia and industry. Commonly, the formation of the carbamate during the CO2 reaction with primary, secondary, and sterically hindered amines is described by a two‐step zwitterion mechanism. Alternatively, a single‐step termolecular reaction mechanism can also be used to govern carbamate formation. The experimental kinetic data for several amine‐based solvents are consistent with this mechanism, and it can satisfactorily explain fractional‐order and higher‐order kinetics. However, up to now, the termolecular reaction mechanism has not been properly discussed. Here, this mechanism is described in detail, a simple procedure to estimate the kinetic parameters is outlined, and the termolecular reaction kinetics for various systems comprising individual and mixed amines is reviewed.

Formation and Decomposition of Chemically Activated and Stabilized Hydrazine

Recombination of two amidogen radicals, NH(2) (X(2)B1), is relevant to hydrazine formation, ammonia oxidation and pyrolysis, nitrogen reduction (fixation), and a variety of other N/H/X combustion, environmental, and interstellar processes. We have performed a comprehensive analysis of the N(2)H(4) potential energy surface, using a variety of theoretical methods, with thermochemical kinetic analysis and master equation simulations used to treat branching to different product sets in the chemically activated NH(2) + NH(2) process. For the first time, iminoammonium ylide (NH(3)NH), the less stable isomer of hydrazine, is involved in the kinetic modeling of N(2)H(4). A new, low-energy pathway is identified for the formation of NH(3) plus triplet NH, via initial production of NH(3)NH followed by singlet-triplet intersystem crossing. This new reaction channel results in the formation of dissociated products at a relatively rapid rate at even moderate temperatures and above. A further novel pathway is described for the decomposition of activated N(2)H(4), which eventually leads to the formation of the simple products N(2) + 2H(2), via H(2) elimination to cis-N(2)H(2). This process, termed as "dihydrogen catalysis", may have significant implications in the formation and decomposition chemistry of hydrazine and ammonia in diverse environments. In this mechanism, stereoselective attack of cis-N(2)H(2) by molecular hydrogen results in decomposition to N(2) with a fairly low barrier. The reverse termolecular reaction leading to the gas-phase formation of cis-N(2)H(2) + H(2) achieves non-heterogeneous catalytic nitrogen fixation with a relatively low activation barrier (77 kcal mol(-1)), much lower than the 125 kcal mol(-1) barrier recently reported for bimolecular addition of H(2) to N(2). This termolecular reaction is an entropically disfavored path, but it does describe a new means of activating the notoriously unreactive N(2). We design heterogeneous analogues of this reaction using the model compound (CH(3))(2)FeH(2) as a source of the H(2) catalyst and apply it to the decomposition of cis-diazene. The reaction is seen to proceed via a topologically similar transition state, suggesting that our newly described mechanism is general in nature.

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Three experimental techniques, laser flash photolysis, redox catalysis, and stopped-flow, were used to investigate the variation of the oxidation rate constant of phenol in neat water with the driving force offered by a series of electron acceptors. Taking into account a result previously obtained with a low-driving force electron acceptor thus allowed scanning more than half an electron-volt driving force range. Variation of the rate constant with pH showed the transition between a direct phenol oxidation reaction at low pH, where the rate constant does not vary with pH, and a stepwise reaction involving the prior deprotonation of phenol by OH(-), characterized by a unity-slope variation. Analyses of the direct oxidation kinetics, based on its variation with the driving force and on the determination of H/D isotope effects, ruled out a stepwise mechanism in which electron transfer is followed by the deprotonation of the initial cation radical at the benefit of a pathway in which proton and electron are transferred concertedly. Derivation of the characteristics of counterdiffusion in termolecular reactions allowed showing that the concerted process is under activation control. It is characterized by a remarkably small reorganization energy, in line with the electrochemical counterpart of the reaction, underpinning the very peculiar behavior of water as proton acceptor when it is used as the solvent.

Organic nitrate formation in the radical-initiated oxidation of model aerosol particles in the presence of NOx

Using a flow tube reactor coupled to a chemical ionization mass spectrometer, the Cl-initiated oxidation of solid and supercooled liquid brassidic acid (BA, trans-13-docosenoic acid) particles was investigated in the presence of NO and NO2. For the first time, organic nitrate formation from the heterogeneous oxidation of model organic aerosols in the presence of NO was observed, but none was formed by the addition of up to 600 ppb of NO2. Also, no nitrate formation was observed in liquid particles, but the nitrate yields in the solid particles were measured to be as large as 6% with a negative temperature dependence over the range 259-293 K. The corresponding effective activation energy of -7.5 (+/-4.4) kJ mol(-1) suggests that the mechanism of particulate organic nitrate formation is analogous to the termolecular gas-phase reaction of . The yields are smaller than those from analogous gas-phase reactions, but this may result from photodissociation of the nitrate by the UV (355 nm) laser for which there is indirect evidence. Additionally, enhanced rates of the RO2+RO2 reactions in the condensed phase could lead to smaller nitrate yields. The results suggest that slower diffusion of the RO2 radicals in the solid particles compared to the liquid particles makes the RO2+NO reaction competitive with the RO2+RO2 reactions and results in nitrate formation near the surface of the particle. The organic nitrates formed in these experiments are observed intact after the reacted particles have been vaporized at temperatures up to 380 degrees C suggesting that they are thermally stable in the troposphere and may enable long-range transport of NOx if they photodissociate on the timescale of days. The findings from these experiments are not specific to unsaturated carboxylic acids but should apply to nearly all particulate hydrocarbons, and they indicate that the particle phase could be important in determining how organic aerosols evolve chemically through radical-initiated oxidation in polluted atmospheres.

Autocatalytic degradation of white phosphorus with silylenes

White phosphorus (P(4)) is prone to undergo degradation by nucleophiles and is reluctant to do so with electrophiles. Silylenes possess a strong singlet character but at the same time bear a largely inert lone pair orbital at the silicon atom. Thus they predominantly react in a similar way to electrophilic carbenes. Due to the poor pi-character of the P-P bonds in white phosphorus, the overlap with the empty orbital for the electrophilic silylene is less facile and results in a relatively large barrier for the addition reaction. The electrophilic approach of the silylene to white phosphorus is catalyzed by addition of a second P(4), forming a trigonal bipyramidal transition state geometry. Its stability towards fragmentation is essentially lower than that of the silyl cation. The entropy contributions for bimolecular versus termolecular reactions are discussed.

Computational chemistry study of reactions, equilibrium and kinetics of chemical CO 2 absorption

The chemical reactions involved in CO 2 absorption in amine systems are studied. For each mechanism, available experimental data are considered and quantum mechanical calculations carried out. Base-catalyzed bicarbonate formation is found to be a likely mechanism for all amine bases, not only tertiary amines. Direct formation of bicarbonate species from carbamate species is found to be unlikely. The carbamate formation has been proposed to take place through a single-step termolecular reaction, or through a two step mechanism with a zwitterionic intermediate. Quantum mechanical calculations suggest that if there is such a zwitterionic intermediate, it is likely to be short-lived. Quantum mechanical calculations together with solvation models are shown to predict the base strength and carbamate stability of different amine solvents with a useful degree of accuracy. Solvent effects and electron donation and withdrawal through bonds are identified as important factors in determining the overall reactivity of different amine solvents. Results suggest a strong correlation between the carbamate stability and base strength of amine solvents and their reaction kinetics.

Determination of the Rate Coefficients for the Reactions IO + NO2 + M (Air) → IONO2 + M and O(3P) + NO2 → O2 + NO Using Laser-Induced Fluorescence Spectroscopy

Laser-induced fluorescence spectroscopy via excitation of the A2pi(3/2) <-- X2pi(3/2) (2,0) band at 445 nm was used to monitor IO in the presence of NO2 following its generation in the reactions O(3P) + CF3I and O(3P) + I2. Both photolysis of O3 (248 nm) and NO2 (351 nm) were used to initiate the production of IO. The rate coefficients for the thermolecular reaction IO + NO2 + M --> IONO2 + M were measured in air, N2, and O2 over the range P = 18-760 Torr, covering typical tropospheric conditions, and were found to be in the falloff region. No dependence of k1 upon bath gas identity was observed, and in general, the results are in good agreement with recent determinations. Using a Troe broadening factor of F(B) = 0.4, the falloff parameters k0(1) = (9.5 +/- 1.6) x 10(-31) cm6 molecule(-2) s(-1) and k(infinity)(1) = (1.7 +/- 0.3) x 10(-11) cm3 molecule(-1) s(-1) were determined at 294 K. The temporal profile of IO at elevated temperatures was used to investigate the thermal stability of the product, IONO2, but no evidence was observed for the regeneration of IO, consistent with recent calculations for the IO-NO2 bond strength being approximately 100 kJ mol(-1). Previous modeling studies of iodine chemistry in the marine boundary layer that utilize values of k1 measured in N2 are hence validated by these results conducted in air. The rate coefficient for the reaction O(3P) + NO2 --> O2 + NO at 294 K and in 100 Torr of air was determined to be k2 = (9.3 +/- 0.9) x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recommended values. All uncertainties are quoted at the 95% confidence limit.

An ICR Study of Ion-Molecules Reactions Relevant to Titan’s Atmosphere: An Investigation of Binary Hydrocarbon Mixtures up to 1 Micron

Results are reported for studies of binary mixtures of hydrocarbons exposed to low-energy electron impact ionization. A variety of experimental methods are used: conventional ICR mass spectrometry, the standard double resonance in an ICR for determination of the precursor ions, and the modulated double resonance ejection in an ICR for the determination of the daughter ions. A flowing afterglow-selected ion flow tube experiment (FA-SIFT) was used for validation and examination of termolecular reactions. An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and the identification of missing reactions and reaction channels. An effort was made to extend the study to the highest pressures possible to determine if any important termolecular reaction channels were present that were not recognized in earlier investigations. A new approach was used here. In the binary mixtures of hydrocarbon gases, mass spectra were obtained as a function of independent pressure changes of both gases. All the mass peaks in the spectra were fitted using existing kinetic data as a starting point. A model of the ion abundances was then produced from the solution of the partial differential equations derived from the kinetics in terms of reaction rate coefficients and initial abundances. The model was fitted to the data for all of the pressures by a least-squares fit to the reaction rate coefficients and initial abundances. The kinetic parameters were then adjusted if required.

Nitric Oxide as an Electron Donor, an Atom Donor, an Atom Acceptor, and a Ligand in Reactions with Atomic Transition-Metal and Main-Group Cations in the Gas Phase

The room-temperature reactions of nitric oxide with 46 atomic cations have been surveyed systematically across and down the periodic table using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Rate coefficients and product distributions were measured for the reactions of first-row cations from K+ to Se+, of second-row cations from Rb+ to Te+ (excluding Tc+), and of third-row cations from Cs+ to Bi+. Reactions both first and second order in NO were identified. The observed bimolecular reactions were thermodynamically controlled. Efficient exothermic electron transfer was observed with Zn+, As+, Se+, Au+, and Hg+. Bimolecular O-atom transfer was observed with Sc+, Ti+, Y+, Zr+, Nb+, La+, Hf+, Ta+, and W+. Of the remaining 32 atomic ions, all but 8 react in novel termolecular reactions second order in NO to produce NO+ and the metal-nitrosyl molecule, the metal-monoxide cation and nitrous oxide, and/or the metal-nitrosyl cation. K+, Rb+, Cs+, Ga+, In+, Tl+, Pb+, and Bi+ are totally unreactive. Further reactions with NO produce the dioxide cations CaO2+, TiO2+, VO2+, CrO2+, SrO2+, ZrO2+, NbO2+, RuO2+, BaO2+, HfO2+, TaO2+, WO2+, ReO2+, and OsO2+ and the still higher order oxides WO3+, ReO3+, and ReO4+. NO ligation was observed in the formation of CaO+(NO), ScO+(NO), TiO+(NO), VO+(NO)(1-3), VO2+(NO)(1-3), SrO+(NO), SrO2+(NO)1,2, RuO+(NO)(1-3), RuO2+(NO)1,2, OsO+(NO)(1-3), and IrO+(NO). The reported reactivities for bare atomic ions provide a benchmark for reactivities of ligated atomic ions and point to possible second-order NO chemistry in biometallic and metal-surface environments leading to the conversion of NO to N2O and the production of metal-nitrosyl molecules.

A Kinetic and Product Study of the Cl + HO2 Reaction

Absolute rate data and product branching ratios for the reactions Cl + HO2 --> HCl + O2 (k1a) and Cl + HO2 --> OH + ClO (k1b) have been measured from 226 to 336 K at a total pressure of 1 Torr of helium using the discharge flow resonance fluorescence technique coupled with infrared diode laser spectroscopy. For kinetic measurements, pseudo-first-order conditions were used with both reagents in excess in separate experiments. HO2 was produced by two methods: through the termolecular reaction of H atoms with O2 and also by the reaction of F atoms with H2O2. Cl atoms were produced by a microwave discharge of Cl2 in He. HO2 radicals were converted to OH radicals prior to detection by resonance fluorescence at 308 nm. Cl atoms were detected directly at 138 nm also by resonance fluorescence. Measurement of the consumption of HO2 in excess Cl yielded k1a and measurement of the consumption of Cl in excess HO2 yielded the total rate coefficient, k1. Values of k1a and k1 derived from kinetic experiments expressed in Arrhenius form are (1.6 +/- 0.2) x 10(-11) exp[(249 +/- 34)/T] and (2.8 +/- 0.1) x 10(-11) exp[(123 +/- 15)/T] cm3 molecule(-1) s(-1), respectively. As the expression for k1 is only weakly temperature dependent, we report a temperature-independent value of k1 = (4.5 +/- 0.4) x 10(-11) cm3 molecule(-1) s(-1). Additionally, an Arrhenius expression for k1b can also be derived: k1b = (7.7 +/- 0.8) x 10(-11) exp[-(708 +/- 29)/T] cm3 molecule(-1) s(-1). These expressions for k1a and k1b are valid for 226 K < or = T < or = 336 and 256 K < or = T < or = 296 K, respectively. The cited errors are at the level of a single standard deviation. For the product measurements, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. HCl product concentrations were determined by IR absorption yielding the ratio k1a/k1 over the temperature range 236 K < or = T < or = 296 K. OH product concentrations were determined by resonance fluorescence giving rise to the ratio k1b/k1 over the temperature range 226 K < or = T < or = 336 K. Both of these ratios were subsequently converted to absolute numbers. Values of k1a and k1b from the product experiments expressed in Arrhenius form are (1.5 +/- 0.1) x 10(-11) exp[(222 +/- 17)/T] and (10.6 +/- 1.5) x 10(-11) exp[-(733 +/- 41)/T] cm3 molecule(-1) s(-1), respectively. These expressions for k1a and k1b are valid for 256 K < or = T < or = 296 and 226 K < or = T < or = 336 K, respectively. A combination of the kinetic and product data results in the following Arrhenius expressions for k1a and k1b of (1.4 +/- 0.3) x 10(-11) exp[(269 +/- 58)/T] and (12.7 +/- 4.1) x 10(-11) exp[-(801 +/- 94)/T] cm3 molecule(-1) s(-1), respectively. Numerical simulations were used to check for interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2 --> OH for detection purposes.

A laser photolysis–resonance fluorescence study of the reactions: I + O3→ IO + O2, O + I2→ IO + I, and I + NO2+ M → INO2+ M at 298 K

Laser flash photolysis coupled to resonance-fluorescence detection of I atoms was used to measure the rate coefficients for the reactions: I + O3 --> IO + O2 (R1), O + I2 --> IO + I (R6) and I + NO2 + M --> INO2 + M (R7). All experiments were conducted under pseudo first-order conditions, and the accuracy of the results was enhanced by online determination of reagent concentrations by optical absorption. Bimolecular rate coefficients for reactions (R1) and (R6) were determined to be k1 = (1.28 +/- 0.06) x 10(-12) and k6 = (1.2 +/- 0.1) x 10(-10) cm3 molecule(-1) s(-1) at 298 +/- 2 K, independent of pressure. Rate coefficients for the termolecular reaction (R7), also at 298 +/- 2 K, were found to be in the falloff region between 3rd and 2nd order behaviour and, when combined with other datasets obtained at higher and lower pressures, were adequately described by a simplified Troe function with the parameters: k7,0 (He, 330 K) = 1.48 x 10(-31) cm6 molecule(-2) s(-1), F(C) (He) = 0.43, and k7, infinity = 1.1 x 10(-10) cm3 molecule(-1) s(-1) for He as bath gas. In N2 (or air) the following parameters were obtained k7,0 (N2, 300 K) = 3.2 x 10(-31) cm6 molecule(-2) s(-1), F(C) ( N2) = 0.48, with k7, infinity set to 1.1 x 10(-10) cm3 molecule(-1) s(-1) as obtained from analysis of the falloff curve obtained in He.

Termolecular one-pot synthesis of symmetrical azines of 4-acetyl-3-arylsydnones. Hydrazone and azine derivatives of 4-acetyl-3-arylsydnones, their spectral characterization and biological properties

Hydrazones of 4-acetyl-3-arylsydnones (2a-o) were prepared by heating 4-acetyl-3-arylsydnones (1α-o) with excess of hydrazine hydrate and the corresponding symmetrical azines (3a-o) were obtained by a termolecular reaction of 4-acetyl-3-arylsydnones with hydrazine hydrate (2: 1 ratio). Hydrazones and azines were screened for their antimicrobial activity and few of these compounds exhibit inhibitory action more than the reference drugs used.

Products of meteoric metal ion chemistry within planetary atmospheres. 1. Mg + at Titan

We report results of quantum chemical calculations of Mg +/ligand bond dissociation energies involving ligands identified as major constituents of Titan's upper atmosphere. Trends identified in these results allow elucidation of the important bimolecular and termolecular reactions of Mg +, and of simple molecular ions containing Mg +, arising from meteoric infall into Titan's atmosphere. Our study highlights, and includes calculated rate coefficients for, crucial ligand-switching and ligand-stripping reactions which ensure that a dynamic equilibrium exists between atomic and molecular ions of Mg +. Neutralization of ionized meteoric Mg is expected to produce the radical MgNC in high yield. The highly polar MgNC radical should provide an excellent nucleation site for condensation of polar (e.g., HCN, CH 3CN, and HC 3N) and highly unsaturated (e.g., C 2H 2, C 4H 2, and C 2N 2) neutrals at comparatively high altitude, leading to precipitation of Mg-doped tholin-like material. The implications for Titan's prebiotic chemical evolution, of the surface deposition of such material (which may feasibly contain magnesium porphyrins, or other bioactive Mg-containing complexes) remain to be assessed.

Activation of C-H / H-H bonds by rhodium(II) porphyrin bimetalloradicals.

Reactivity, kinetic, and thermodynamic studies are reported for reactions of a rhodium(II) bimetalloradical with H(2), and with the methyl C-H bonds for a series of substrates CH(3)R (R = H, CH(3), OH, C(6)H(5)) using a m-xylyl diether tethered diporphyrin ligand. Bimolecular substrate reactions involving the intramolecular use of two metalloradical centers and preorganization of the four-centered transition state (M*...X...Y*...M) result in large rate enhancements as compared to termolecular reactions of monometalloradicals. Activation parameters and deuterium kinetic isotope effects for the substrate reactions are reported. The C-H bond reactions become less thermodynamically favorable as the substrate steric requirements increase, and the activation free energy (DeltaG++) decreases regularly as DeltaG degrees becomes more favorable. An absolute Rh-H bond dissociation enthalpy of 61.1 +/- 0.4 kcal mol(-1) is directly determined, and the derived Rh-CH(2)R BDE values increase regularly with the increase in the C-H BDE.

Quantum-mechanical calculations on pressure and temperature dependence of three-body recombination reactions: application to ozone formation rates.

A quantum-mechanical model is designed for the calculation of termolecular association reaction rate coefficients in the low-pressure fall-off regime. The dynamics is set up within the energy transfer mechanism and the kinetic scheme is the steady-state approximation. We applied this model to the formation of ozone O + O2 + M --> O3 + M for M = Ar, making use of semiquantitative potential energy surfaces. The stabilization process is treated by means of the vibrational close-coupling infinite order sudden scattering theory. Major approximations include the neglect of the O3 vibrational bending mode and rovibrational couplings. We calculated individual isotope-specific rate constants and rate constant ratios over the temperature range 10-1000 K and the pressure fall-off region 10(-7)-10(2) bar. The present results show a qualitative and semiquantitative agreement with available experiments, particularly in the temperature region of atmospheric interest.