bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quasi‐steady‐state approximations in air pollution modeling: Comparison of two numerical schemes for oxidant prediction
Authors: Hesstvedt Eigil , Hov Öystein , Isaksen Ivar S. A. 
Published: January 2005

AbstractA numerical method to solve the set of differential equations which describes the chemical development in polluted air is presented. The photochemical lifetimes, continuously monitored for all compounds, determine how the integrations are performed at all times. Components with lifetimes less than 10% of the time step, which is taken as 30 sec, are assumed to be in photochemical equilibrium, while compounds with photochemical lifetimes greater than 100 times the time step are computed according to Euler's method. All other components are calculated from the exponential solution of the continuity equation. The computational accuracy may be improved by iteration on components assumed to be determined by the instant values of other components. The convergence of the iteration is speeded up by ordering the short‐lived compounds in a hierarchical sequence. Since computational errors connected with QSSA methods are difficult to assess, comparison with an automatic scheme is necessary. Our method has been compared with Gear's method for a range of model mixtures of hydrocarbons, nitrogen oxides, and air, thought to cover most conceivable situations of atmospheric pollution. The agreement with Gear's method is within a few percent for all components all the time, in most cases even within 1%. No accumulation of deviations occur during long‐term integrations (e.g., 48 hr with day and night shiftings), and differences which appear during periods with strong concentration gradients (e.g., after sunrise) vanish when the activity has culminated. The method presented here is considerably more efficient than Gear's method, with respect to both computer time and storage.
Absolute rate constants for the reactions of O(3P) atoms and OH radicals with SiH4 over the temperature range of 297–438°K
Authors: Atkinson R. , Pitts J. N. 
Published: January 2005

AbstractAbsolute rate constants for the reaction of SiH4 with O(3P) atoms and OH radicals have been determined over the temperature range 297°–438°K using flash photolysis–NO2 chemiluminescence and flash photolysis–resonance fluorescence techniques, respectively. The Arrhenius expressions obtained are

where the error limits in the Arrhenius activation energies are the estimated overall error limits. Rate data for the reactions of SiH4, CH4, and H2S with O(3P), H, and F atoms and with OH, CH3, and CF3 radicals are compared, showing that H2S and SiH4, which have similar bond energies, have reasonably similar reactivities toward these atoms and radicals.
Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine‐T in aqueous solution
Authors: Mahadevappa D. S. , Jadhav M. B. , Naidu H. M. K. 
Published: January 2005

AbstractThe kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine‐T (CAT) is studied in HClO4 and NaOH media with OsO4 as a catalyst in the latter medium. In acid medium, the rate law is ‐d [CAT]/dt = k [CAT][DMSO][H+]. Alkali retards the reaction and the rate law takes the form ‐d [CAT]/dt = k [CAT][DMSO][OsO4]/[NaOH], but is reduced to ‐d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied.The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO4 which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine‐T and the substrate.
A new mechanism for the reaction of ozone with olefins
Authors: Dodge Marcia C. , Arnts Robert R. 
Published: January 2005

AbstractA mechanism for ozone–olefin reactions is developed that is consistent with the recent findings of several investigations. These findings suggest a reaction sequence leading to the production of fewer free radical species than has been assumed in the past. Computer simulations using the new mechanism reproduce experimental results obtained from the ozonolysis of propylene in air.
A simple preparation of stable, nonreactive surfaces for gas kinetic studies of reactions of hydrogen atoms
Authors: Sepehrad Abolghassem , Marshall Roger M. , Purnell Howard 
Published: January 2005

AbstractA quartz surface has been prepared for which γ, the mean collisional efficiency for removal of hydrogen atoms, is given by

over the temperature range from 315 to 818 K. The preparation “cleans” the surface by contact with 10M aqueous NaOH for ˜ 15 hr and then deactivates it by contact with 10M aqueous HNO3 for ˜15 hr. The surface is stable and long‐lived even after prolonged contact with air. Preliminary results show that a similar result can be obtained using Pyrex glass surfaces.
Kinetics of the reaction HO2 + NO2(+M) = HO2NO2 using molecular modulation spectrometry
Authors: Cox R. A. , Patrick K. 
Published: January 2005

AbstractRate constants for the reaction HO2 + NO2(+ M) = HO2NO2(+ M) have been obtained from direct observations of the HO2 radical using the technique of molecular modulation ultraviolet spectrometry. HO2 was generated by periodic photolysis of Cl2 in the presence of excess H2 and O2, and k1 was determined from the measured concentrations and lifetime of HO2 with NO2 present. k1 increased with pressure in the range of 40–600 Torr, and a simple energy transfer model gave the following limiting second‐ and third‐order rate constants at 283 K: k1∞ = 1.5 ± 0.5 × 10−12 cm3/molec·sec and k1III = 2.5 ± 0.5 × 10−31 cm6/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195–265 nm; it showed a broad feature with a maximum at 200 nm, σmax = 4.4 × 10−18 cm2.
Abstraction of chlorine atoms from chloroalkanes. V. The liquid‐phase reaction between Et3SiH radicals and CH2Cl2, CHCl3, CCl4, and CCl3CN
Authors: Aloni R. , Rajbenbach L. A. , Horowitz A. 
Published: January 2005

AbstractThe kinetics of chlorine transfer from CH2Cl2, CHCl3, CCl4, and CCl3CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1‐bromopentane was used as a reference. The following Arrhenius parameters were determined:magnified imagewhere the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et3Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.
The kinetics of the solvolysis of propylene and cyclopropane in concentrated aqueous sulfuric acid relative energies of the 2‐propyl cation and protonated cyclopropane
Authors: Viviani Donn , Levy Joseph B. 
Published: January 2005

AbstractThe rates of solvolysis of propylene and cyclopropane in 6.49M H2SO4 have been measured as a function of temperature. From the data, calculations of the relative heats of formation in solution of the 2‐propyl cation and protonated cyclopropane have been made. The heat of formation of protonated cyclopropane has been found to be 6.4 kcal/mol greater than that of the 2‐propyl cation. The implications of this result are discussed.
Very low‐pressure pyrolysis (VLPP) of hex‐1‐ene. Kinetics of the retro‐ene decomposition of a mono‐olefin
Authors: King Keith D. 
Published: January 2005

AbstractThe thermal unimolecular decomposition of hex‐1‐ene has been investigated over the temperature range of 915–1153 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C3−C4 fission and retro‐ene elimination, with the latter dominant at low temperatures and the former at high temperatures. This behavior results in an isokinetic temperature of 1035 K under VLPP conditions (both reactions in the unimolecular falloff regime). RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters given by log k1 (sec−1) = (12.6 ± 0.2) ‐(57.7 ± 1.5)/θ for retro‐ene reaction, and log k2 (sec−1) = (15.9 ± 0.2) ‐ (70.8 ± 1.0)/θ for C‐C fission, where θ = 2.303 RT kcal/mol. The A factors were assigned from the results of a recent shock‐tube study of the decomposition in the high‐pressure regime, and the activation energies were found by matching the RRKM calculations to the VLPP data. The parameters for C‐C fission are consistent with the known thermochemistry of n‐propyl and allyl radicals. A clear measure of the importance of the molecular pathway in the decomposition of a mono‐olefin has been obtained.
The kinetics of the gas‐phase thermal isomerization and decomposition of Trans‐ and Cis‐1,2‐Bis(trifluoromethyl)‐1,2,3,3‐tetrafluorocyclopropane
Authors: Ferrero Juan C. , Staricco Eduardo H. 
Published: January 2005

AbstractThe kinetics of the gas‐phase thermal isomerization between trans‐ and cis‐1,2‐bis(trifluoromethyl)‐1,2,3,3‐tetrafluorocyclopropane as well as their decomposition to trans‐ and cis‐perfluoro‐2‐butene, respectively, and CF2, was studied in the temperature range of 473–533°K, with an initial pressure of reactant of 1.5 to 7.0 Torr. Some runs were also made with the addition of SF6 as an inert gas up to a total pressure of 100 Torr. The reactions are first order and homogeneous. The rate constants for the geometrical isomerization fit the following Arrhenius relations:

and the corresponding equations for the decomposition of the trans and cis‐cyclopropane are

.
The reaction of CH3O2 radicals with NO2
Authors: Adachi Hiroyuki , Basco Norman 
Published: January 2005

AbstractThe rate constant for the reaction CH3O2 + NO2 → (products) has been measured directly by flash photolysis and kinetic spectroscopy. At room temperature and at total pressures between 53 and 580 Torr, k3 = (9.2 ± 0.4) × 108 liter/mole sec so that the rate of formation of the probable primary product peroxymethyl nitrate (CH3O2NO2) may be significant in urban atmospheres.
A reinvestigation of the temperature dependence of the rate constant for the reaction O + O2+ M → O3+ M (for M = O2, N2, and Ar) by the flash photolysis resonance fluorescence technique
Authors: Klais Odo , Anderson Philip C. , Kurylo Michael J. 
Published: January 2005

AbstractThe flash photolysis resonance fluorescence technique has been used to reinvestigate the kinetics of the oxygen atom–oxygen molecule combination reaction. Third‐order rate constants for O2, N2, and Ar as deactivant molecules were determined over the temperature range of 219–368 K. The results presented herein are the most extensive data sets available for atmospheric modeling and are used to formulate a recommendation for such purposes. The recommended rate expressions areorComparisons of these results with existing literature data are presented.
Kinetics of formation of HCN during pyridine pyrolysis
Authors: Houser Thomas J. , Hull Mitchell , Alway Robert M. , Biftu Tesfaye 
Published: January 2005

AbstractThe rate of HCN evolution during the inert pyrolysis of pyridine in the temperature range of 900–1000°C was determined in a flow system using a stirred‐flow reactor. The data indicated that HCN was formed through a sequence of reactions rather than during the initial step(s) involving the disappearance of pyridine. The Arrhenius parameters for the first‐order step yielding HCN were 39.5 kcal/mol and 6.8 for the activation energy and log frequency factor, respectively. The mechanistic implications of the rate data are discussed, and these are related to the overall pyridine pyrolysis mechanism.
A computational analysis of the alkane pyrolysis mechanism: Sensitivity analysis of individual reaction steps
Authors: Edelson D. , Allara D. L. 
Published: January 2005

AbstractThe previously reported extensive mechanism for the pyrolysis of propane and n‐butane around 800 K is reexamined in the light of a recent reevaluation of the rate constant data base, and the sensitivity of model simulations to variations in the rate parameters is studied. The pyrolysis rates of butane and the product distribution of propane remain in good agreement with the available experiments, while the rate of propane and the product distribution of butane now show significant differences. The linear sensitivity analysis of the reaction matrix demonstrates an intimate coupling between initiation, hydrogen abstraction, radical decomposition, and recombination reactions as primarily responsible for the overall behavior of the mechanism. The role of unsaturated radicals in the self‐inhibition of the pyrolysis process is quantitatively established. The study of the sensitivity coefficients for butane product formation has permitted pinpointing those specific reaction steps in the mechanism which are most likely responsible for the remaining discrepancies between model and experiment. This particular example demonstrates the usefulness of sensitivity calculations for the isolation of reactions for which improvements in rate parameter values are needed.
Kinetics of the reaction Cl + HO2 = HCl + O2, using molecular modulation spectrometry
Authors: Cox R. A. 
Published: January 2005

AbstractThe rate constant for the reaction (1), Cl + HO2 → HCl + O2, was measured using molecular modulation spectrometry to investigate HO2 radical kinetics in the modulated photolysis of Cl2;H2O2 mixtures at 760 torr pressure. HO2 was monitored directly in absorption at 220 nm, and k1 was determined from computer simulations of the observed kinetic behavior of HO2, using a simple chemical model. The results gave

where k4 is the rate constant for the reaction of Cl with H2. A consensus value of k4 gave k1 = 6.9 × 10−11 cm3/molecule sec, independent of temperature in the range of 274–338 K with an overall uncertainty of ±50%. The relative importance of reaction (1) for the conversion of Cl to HCl in the stratosphere is discussed briefly.
Kinetics and mechanism of the germane decomposition
Authors: Newman C. G. , Dzarnoski J. , Ring M. A. , O'Neal H. E. 
Published: January 2005

AbstractThe homogeneous gas‐phase thermal decomposition kinetics of germane have been measured in a single‐pulse shock tube between 950 and 1060 K at pressures around 4000 torr. The initial decomposition is GeH4 → GeH2 + H2 in its pressure‐dependent regime, with log k = 13.83 ± 0.78 – 50,750 ± 3570 cal/2.303RT. RRKM calculations suggest that the high‐pressure Arrhenius parameters are log k GeH4(M → ∞) = 15.5 – 54,300 cal/2.303RT. Extrapolations to static system pyrolysis conditions (T ∼ 600 K, P ∼ 200 torr) give homogeneous reaction rates which are much slower than those observed, hence the static system pyrolysis of germane must be predominantly heterogeneous. Shock‐initiated pyrolysis reaction stoichiometry is 2 mol H2 per mole GeH4, suggesting that the subsequent decomposition of germylene is essentially quantitative. Investigations of the hydrogen product yields for pyrolysis of GeD4 in øCH3 further indicate that the germylene decomposition reaction is mainly GeH2 → H2 + Ge, but that a small amount of reaction to H atoms may also occur.
Mutual interactions of the methyl and methylperoxy radicals studied by flash photolysis and kinetic spectroscopy
Authors: Adachi Hiroyuki , Basco N. , James D. G. L. 
Published: January 2005

AbstractThe decadic extinction coefficient of the methyl radical at 216.4 nm and the rate constant for mutual combination were redetermined as:

. The application of the Beer–Lambert law to these measurements was justified experimentally. The absorption spectrum of the methylperoxy radical was characterized as a weak, broad, structureless band, having a maximum at 240 nm with ϵ(240) = 1.55 × 103 l./mol cm. The mutual interaction of methylperoxy radicals leads to the generation of methoxy and hydroperoxy radicals as a consequence of the nonterminating interaction

. Each derivative radical may consume a significant fraction of the methylperoxy radicals, and either of these cross interactions may be made predominant by a suitable choice of oxygen pressure. The mutual interaction was studied under both conditions. The overall mechanism was analyzed by a precise computational method, and the rate constant of the total mutual interaction

was estimated as

.
The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media
Authors: Brusa M. A. , Colussi A. J. 
Published: January 2005

AbstractThe reaction between formic acid and bromine in strongly acid aqueous media at 298 K

was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = ‐d[Br2]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br2[(2.7–13.6) × 10−3M], H+ (0.03–2.0M), and Br− (up to 0.6M). The mechanism
equation image
with k1 = 20.2 ± 1.2 M−1 sec−1, pK2 = 3.76, pK3 = −1.20, accounts for all experimental observations. Br3− and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.
Effect of brownian diffusion on chemical kinetics
Authors: Sitarski M. 
Published: January 2005

AbstractA new method of theoretical prediction of the kinetic rate constants of fast chemical reactions in solutions is presented. It takes into account the effect of finite diffusive displacements of the reacting molecules. The approach is based on the solution of the steady‐state Fokker–Planck equation by the moments method of Grad developed in the theory of coagulation of aerosol particles. A comparison of the predicted rate constants with the experimental data provided by Schuh and Fischer for the self‐reaction of tert‐butyl radicals in n‐alkanes shows a good correspondence.
Kinetic studies of free radical reactions by mass spectrometry. II. The reactions of SO + ClO, SO + OClO and SO + BrO
Authors: Clyne Michael A. A. , Macrobert Alexander J. 
Published: January 2005

AbstractThe rates of several novel elementary reactions involving ClO, BrO and SO free radicals in their ground states were studied in a discharge‐flow system at 295 K, using mass spectrometry. The rate constant k2 was determined from the decay of SO radicals in the presence of excess ClO radicals:

The SO + OClO overall reaction has a complex mechanism, with the primary step having a rate constant k5 equal to (1.9 ± 0.7) × 10−12 cm3 sec−1:

A lower limit for the rate constant of the rapid reaction of SO radicals with BrO radicals was determined:
Effect of cyano group substitution on metathetical reactions. IV. Substituent effects on the rates of cyanomethyl radical reaction with haloalkanes
Authors: Gonen (Geliebter) Y. , Horowitz A. , Rajbenbach L. A. 
Published: January 2005

AbstractGamma radiation‐induced free radical chain reactions in liquid mixtures of BrCH2CN, eyelohexane (RH), and haloalkanes (XCCl3) were studied. The kinetics of hydrogen and chlorine atom abstraction from CHCl3, CH3CCl3, CH2ClCCl3, CHCl2CCl3, CF3CCl3, C2Cl6, CCl3CN, and CCl4 by CH2CN radicals were investigated by a competitive method. The reactions investigated were
equation image
Rate constant ratios k3/k2, k5/k6, k7/k2, and k3/k7 were determined at 180°C. In the CCl4RHBrCH2CN system k3/k2 was determined in the temperature range of 100–180°C, yielding log k2 k3 = −0.11 ± 0.2 −(3.34 ± 0.39/θ): where θ = 2.3RT in kcal/mol. The value E2E3 was combined with existing data on E3 to yield E2(CCl4) = 17.57 kcal/mol. The reactivity trend of CH2CN is compared with that of R radicals. It is shown that in spite of a difference of about four orders of magnitude in kCl values, the reactive cyclohexyl radical is somewhat more selective than CH2CN. It is proposed that the relative reactivities log[k2(XCCl3)/k2(CH3CCl3)] can be correlated in terms of a dual‐parameter Taft equation which takes into account both resonance and inductive substituent effects.
Very low‐pressure pyrolysis (VLPP) of pentynes. I. Kinetics of the retro‐ene decomposition of pent‐1‐yne
Authors: King Keith D. 
Published: January 2005

AbstractThe thermal unimolecular decomposition of pent‐1‐yne has been investigated over the temperature range of 923–1154 K using the technique of very low‐pressure pyrolysis (VLPP). Under the experimental conditions the reaction proceeds predominantly via a molecular retro‐ene pathway to yield allene and ethylene. There was some evidence for the occurrence of the higher energy C3C4 bond fission pathway at the high end of the temperature range. Interpretation of the data with the aid of RRKM theory and taking into account a decrease in gas‐wall collision efficiency with temperature yields the following high‐pressure rate constant expression for the retro‐ene pathway:

at 1100 K where θ = 2.303 RT kcal/mol and the A factor was assigned from the results of shock‐tube studies of similar molecules. These rate parameters are independent of the inclusion of the bond fission pathway in the RRKM calculations. The results are compared with previous data on the retro‐ene decomposition of alkynes.
An indirect measurement of the absolute rate constant of the self‐reaction of tert‐butoxy radicals
Authors: Wong S. King 
Published: January 2005

AbstractNo reliable rate constant is available for the self‐reaction of tert‐;butoxy radicals. We have set up a competition between hydrogen abstraction and self‐reaction of tert‐butoxy radicals in a flash photolysis electron spin resonance study to extract this information. Experimental values of hydrogen abstraction product radical concentrations under various hydrogen donor concentrations were then compared with theoretically calculated values with different values of 2k4 to obtain the best fit. Hydrogen donors such as cyclopentane, anisole, methyl tert‐butyl ether, and methanol were chosen for the study. A value of (1.3 ± 0.5) × 109M−1 sec−1 for the rate constant of the self‐reaction of tert‐butoxy radicals has been determined at 293°K.
Kinetics of acid catalyzed and Ag(I) catalyzed decomposition of peroxodisulfate in aqueous medium
Authors: Singh U. Chandra , Venkatarao K. 
Published: January 2005

AbstractThe mechanism of acid catalyzed decomposition of peroxodisulfate, (S2O) in aqueous perchlorate medium involves the hydrolysis of the species H2S2O8 and HS2O and the homolysis of the species H2S2O8, HS2O and S2O at the OO bond. The overall rate law when 1.4M > [HClO4] > 0.1M is

The constants k′ and k″ contain the hydrolysis and homolysis rate constants of HS2O8− and H2S2O8, respectively. With added Ag(I), the acid catalyzed and Ag(I) catalyzed reactions take place independently. Ag(I) catalyzed decomposition appears to involve the species AgS2O (aq).
The rate of reaction of methyl radicals with ozone
Authors: Ogryzlo E. A. , Paltenghi R. , Bayes Kyle D. 
Published: January 2005

AbstractThe absolute rate constant for the reaction of methyl radicals with ozone has been measured as a function of temperature. Small concentrations of CH3 were generated by flash photolyzing CH3NO2 at 193 nm with an ArF laser. A photoionization mass spectrometer was used to follow the rate of decay of CH3 at various ozone concentrations. The resulting rate constants could be fit by the expressions

over the temperature range of 243–384 K. These rate constants can be modeled by simple transition state theory using reasonable parameters for the activated complex. Use of this rate constant shows that less than 1% of the methyl radicals formed in the stratosphere react with ozone.