bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the gas‐phase reaction between iodine and monosilane and the bond dissociation energy D(H3SiH)
Authors: Doncaster Alan M. , Walsh Robin 
Published: January 2005

AbstractThe title reaction has been investigated in the temperature range of 494–545 K. During the early stages of reaction the only observed products were silyl iodide and hydrogen iodide. Initial rates were found to obey the rate law
equation image
over a wide range of initial iodine and monosilane pressures. Secondary reactions, most probably of SiH3I with I2, became more important as the reaction progressed. However, provided [SiH4]0/[I2]0 > 20, these secondary processes had a negligible effect on the kinetics, and an integrated rate expression could be used. These kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step
equation image
has been deduced. From this the bond dissociation energy D(SiH3H) = 378 ± 5 kJ/mol (90 kcal/mol) is obtained. The kinetic and thermochemical implications of this value, especially to the pyrolysis of monosilane, are discussed.
Photolysis of ethyl‐iodide in lithium chloride glassy aqueous solutions with light, λ = 254 nm at 77 K
Authors: Burbo E. M. , Gurman V. S. 
Published: January 2005

AbstractThe photolysis of C2H5I in a glassy salt matrix (5M, 7.5M, 10M) of aqueous LiCl at 77 K with light of λ = 254 nm has been conducted, product analysis being by ESR and UV spectroscopy. The electrolytic medium causes the ionization of product HI, and I− concentrations can be continuously determined. During photolysis [I−] is less than the amount of C2H5I decomposed. But after photolysis thaw‐freeze cycling is accompanied by progressive growth in [I−] until the yield matches the C2H5I loss, the quantum yields being 0.26, 0.20, and 0.17 for the three LiCl solutions, respectively. The quantum yield of unionized HI is unchanged, however, at around 0.36, the overall change being due to a fall in the extent to which the HI is ionized in the direct photolysis (ø = 0.22, 0.16, and 0.11). It is proposed that this is a consequence of the density increase of matrix packing as the LiCl concentration is increased so that fewer HI are in contact with the aqueous medium and cage recombination is favored.The results establish that the primary reaction is essentially exclusive:
equation image
and that substantial aggregates of C2H5I exist within which HI are caged and cannot be ionized. The direct reaction

occurs only to a trivial extent, ø; = 10−4, C2H5 arising virtually totally via
The estimation of a factors for atom fissions in polyatomics
Authors: Ghibaudi E. , Colussi A. J. 
Published: January 2005

AbstractIt is shown that A factors for atom fissions in polyatomics can be reliably estimated by an improved version of the restricted free rotor model (RFRM). No adjustable parameters are used in the evaluation of A factors for the dissociation of the ROF bond (R: NO2, SF5, CF3, FSO2), and the authors' predictions are compared with high‐pressure kinetic data for these reactions. In the case of O2NOF, for which full spectroscopic information is available, RFRM reproduces the observed value Am well within a factor of 2. Similar agreement is reached for F5SOF and FO2SOF, assigning reasonable limits to their OF torsional frequencies. For F3COF, Am and the calculated back reaction rate constant, which is independent of the model, are both much too small to be plausible, suggesting falloff effects rather than a failure of RFRM.
Infrared photochemistry of cyclobutyl chloride
Authors: Francisco J. S. , Steinfeld J. I. 
Published: January 2005

AbstractThe decomposition of cyclobutyl chloride following multiple infraredphoton excitation has been investigated. The primary photolysis products are butadiene, from elimination of HCl, and ethylene and vinyl chloride, fromring scission. The vinyl chloride undergoes secondary decomposition to acetylene and HCl. In addition to these products, known from thermal VLPP experiments, we also find 1‐butene, which may arise from a higher energy CCl homolysis channel. Collisions with either reactant molecules oradded buffer gas lead to cooling of the laser‐produced vibrational energy distributions. The average amount of energy removed per collision is 15–20 kcal/mol for self‐collisions and 2–4 kcal/mol with argon.
The kinetics and the mechanism of the thermal decomposition of bis(trifluoromethyl) trioxide. The influence of carbonmonoxide on its decomposition
Authors: Czarnowski J. , Schumacher H. J. 
Published: January 2005

AbstractThe kinetics of the thermal decomposition of CF3O3CF3 has been investigated in the pressure range of 15–599 torr at temperatures between 59.8 and 90.3°C and also in the presence of CO between 42 and 7°C. The reaction is homogeneous. In the absence of CO the only reaction products are CF3O2CF3 and O2. The rate of reaction is strictly proportional to the trioxide pressure, and is not affected by the total pressure, the presence of inert gases, and oxygen.

The following mechanism explains the experimental results:
equation image
In the presence of CO there appear CO2, (CF3OCO)2, and CF3O2C(O)OCF3 as products. With increasing temperature the amount of peroxicarbonate decreases, while the amounts of oxalate and CO2 increase. The rate of decomposition of the trioxide above a limiting pressure of about 10 torr CO is strictly first order and independent of CO pressure, total pressure, and the pressure of the products.

equation image
The addition of larger amounts of O2 to the CO containing system chaqnges the course of the reaction.
The temperature coefficient of the rates in the system Cl + CH4 ⇆ CH3 + HCl, thermochemistry of the methyl radical
Authors: Heneghan Shawn P. , Knoot Peter A. , Benson Sidney W. 
Published: January 2005

AbstractThe bimolecular rate constant for the title reaction has been measured by very‐low‐pressure reactor techniques at 233 < T K < 338. The equilibrium constant has also been measured between 253 and 338 K. Our rate constants are in excellent agreement with recent measurements using very different techniques and reaction conditions, and the general agreement probably makes this one of the most accurately measured rateconstants. Transition state models of the reaction rule out a bent TS in favor of a TS with colinear Cl···H···C bonds. The curvature at higher temperatures (>350 K) is quantitatively accounted for by transition state theory analysis. Tunneling is shown not to play a role. The measured values of K1 allow an experimental value of S° (CH3) to be fixed to only ±2.4 e.u. However, using known values of S° for all species gives ΔH°f298(CH3.) = 35.1 plusmn; 0.1 kcal/mol in excellent agreement with other measured values.
Comparison of the kinetics of cathodic H2 evolution from the unhydrated H3O+ ion and its hydrated form H9O: Frequency factor effects and modes of activation
Authors: Conway B. E. , Tessier D. F. 
Published: January 2005

AbstractExperiments are described in which the kinetics of cathodic hydrogen evolution from the unhydrated H3O+ ion in pure CF3SO H3O+ are compared with those from an aqueous solution of CF3SO3H where the proton is mainly in a fully hydrated state as H9O. From the acid hydrate, which exists mainly as the ionic compound CF3SOH3O+, rates of H2 evolution at Ni, Pt, and Hg electrodes, measured at a given overpotential or expressed as exchange current densities, are between about 3.5 and 20 times slower than those from the same electrolyte in dilute (1.0M) aqueous solution. Allowing for the concentration differences in these two types of system and double‐layer effects, the rate constants are between about 9.4 and 216 times smaller for the reaction from H3O+ than from H9O at the above electrodes.The evaluation of apparent heats of activation for H2 evolution from the two types of proton sources allows ratios of real frequency factors to be calculated for discharge from H3O+ and H9O. These data have a bearing on the theoretical conclusions regarding proton discharge mechanisms and show that frequency factor effects can be as important as activation energy differences in determining the rates of proton discharge from different proton sources.The results are discussed in terms of current ideas about electron and proton transfer in electrochemical reactions, the state of hydration of H+, and the role of discharge from paired CF3SO and H3O+ ions. In particular, the molecular mechanics of discharge of the proton from the molecular ion H3O+ can be different from that from the fully hydrated H+ ion where many more HO‐ vibrational and librational modes can be involved in the process of activation of the H9O entity.
Quasi‐classical trajectory calculations on the H + O2 reaction
Authors: Bottomley Margaret , Bradley John N. , Gilbert James R. 
Published: January 2005

AbstractQuasi‐classical trajectory calculations have been performed on the H + O2 system. Significant reaction probabilities are obtained when the initial energy is in rotation or vibration, or a combination of the two, but not when the initial energy is in translation. The opacity function shows a bimodal dependence on the impact parameter, with a small peak at 0.9 Å < b < 1.5 Å and a very prominent peak at 2.5 Å < b < 3.3 Å. The product scattering angles and product energy distributions also depend on b and to a limited extent on the initial energy distribution.The observations can be largely interpreted in terms of the nature of the motion on the potential energy surface, while the effects of rotational energy on the reaction follow qualitatively from statistical phase‐space theory.
Electron transfer between trans‐dihydroxotetraoxoosmate(VIII) and thiosulfate. A kinetic study in aqueous alkaline media
Authors: Panda Rama Krushna , Neogi Gautam , Ramaswamy D. 
Published: January 2005

AbstractThe kinetics of oxidation of thiosulfate to tetrathionate by trans‐dihydroxotetraoxoosmate(VIII) in aqueous alkaline media have been studied. The oxidation follows a rate expression

where KOs is the formation constant of trans‐dihydroxotetraoxoosmate (VIII), and K2 and k3, respectively, represent the formation constants of the intermediate complex involving Os(VIII) and S2O and its decomposition constant. The KOs, K2, and k3 values have been computed to be (19.5 ± 3) dm3/mol, (6.12 ± 0.5) and (3.32 ± 0.3) × 10−1 dm3/mol s at 303 K, and I = 0.32 mol/dm3, respectively. The rate law is consistent with a mechanism envisaging the equilibrium formation of an intermediate complex involving Os(VIII) and S2O, followed by a rate‐determining decomposition of the complex with concomitant electron transfer.
Unimolecular activation–deactivation: Impulsive collision theory
Authors: Schranz Harold W. , Nordholm Sture 
Published: January 2005

AbstractA theory of collisional energy transfer based on microcanonical relaxation in the limit of infinitesimal collision lifetimes is developed. In distinction to the recently formulated ergodic collision theory the potential energy is now frozen due to the short time scale, and only kinetic energy is available for redistribution. As a consequence, the rate of energy transfer is decreased, and agreement with experimentally based estimates generally improved.
Enhancement of the bimolecular reaction of hydrogen iodide by vibrational excitation
Authors: Horiguchi Hiroyuki , Tsuchiya Soji 
Published: January 2005

AbstractThe bimolecular reaction of HI in CO2, which was excited vibrationally by irradiation of a continuous‐wave CO2 laser light, was investigated in the temperature range of 721–980 K. An enhancement of the reaction rate by a factor of about 2.5 was observed in the 1:1 HICO2 mixture in comparison with the rate in pure HI when both sample gases were irradiated by a CO2 laser (50 W) at 1 torr. However, in the HI‐SF6 mixtures the decomposition rate of HI was not accelerated by irradiation of the CO2 laser. Thus the enhancement is attributed to vibrational excitation of HI through collisional energy transfers from laser‐excited CO2 (00°1). At lower total pressures or at lower partial pressures of HI in HI‐CO2 mixtures the enhancement was more significant because of inefficient vibrational deactivation of excited HI. A model calculation gave the result in agreement with the experimental one if the effective activation energy is assumed as Ea† = Ea ‐ αEvib, where Ea is the activation energy for the thermal reaction, Evib is the vibrational energy of two colliding HI molecules, and α is estimated to be about 0.7. This means that a part of the vibrational energy of reacting HI is employed to reduce the activation energy for the translational or rotational degree of freedom.
O(3P) + HOONO2 → products: Temperature‐dependent rate constant
Authors: Chang Jenq‐sian , Trevor Paula L. , Barker John R. 
Published: January 2005

AbstractThe title reaction was studied in a stirred‐flow reactor at six temperatures ranging from 228 to 297 K and for pressures near 2 torr. The experiments were performed under O‐atom‐rich conditions, and the HOONO2 concentration was monitored with a modulated molecular‐beam mass spectrometer. O‐atom concentrations were measured by titration with NO2 and by monitoring the portion of O2 dissociated in the microwave discharge. A weighted least‐squares analysis gives (k ± 1σ) = (7.0 ± 12.2) × 10−11 exp(‐3369 ± 489/T) cm3/s, where the uncertainties are 1 standard deviation (six temperatures) the covariance was σAB = 5.97 × 10−8. Due to the possible presence of systematic errors, the uncertainty in the rate constant could be as great as a factor of 2 over the entire temperature range.
Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato‐O)‐chromium(2+) ion
Authors: Hansen Peter J. , Birk James P. 
Published: January 2005

AbstractThe kinetics of the aquation of (H2O)5Cr(O2CCCl3)2+ have been examined at 35–55°C and 1.00M ionic strength with [H+] = 0.01−1.00M. The reaction follows the rate equation ‐d ln [Crtotal]/dt = (a[H+]−1 + b + c[H+])/(1 + d[H+]), where [Crtotal] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10−7M/s, b = (1.66 ± 0.02) × 10−5 s−1, c = (7.0 ± 0.8) × 10−5M−1·S−1 and d = 2.3 ± 0.3M−1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady‐state intermediates. Equilibrium and activation parameters were determined.
The kinetics of isotope exchange reactions: Use of initial rates to measure isotope effects on carbon acid ionization
Authors: Kresge A. J. , Powell M. F. 
Published: January 2005

AbstractMultistep hydrogen isotope exchange reactions, such as the íonization of a carbon acid via a carbanion intermediate in a protic solvent, when conducted using an isotopic tracer to monitor the exchange, have the unusual feature that their rate‐determining steps always refer to the transfer of the tracer isotope and never to the isotope present in macroscopic amounts. This property of these reactions is discussed and rationalized using a free energy versus reaction coordinate diagram. It is further shown that this property does not invalidate a commonly used method of measuring kinetic isotope effects on carbon acid ionization in which rates of incorporation of tritium tracers into RH and RD substrates are compared, despite the fact that tritium transfer is rate determining in both exchanges, but it is valid only if initial rate measurements are used. When the comparison is made in a protio solvent, e.g., H2O, the portion of the initial reaction which may be used depends strongly on the magnitude of the isotope effect. It ranges from less than 1% tritium incorporation for large isotope effects to 10% or more for isotope effects near unity. On the other hand, when a deuterated solvent, e.g., D2O, is used, the range of validity of the method for large isotope effects is extended dramatically.
Vibrational energy transfer from chemically activated 1,4‐cyclohexadiene
Authors: Orchard S. Walter , Ramsden Jennifer 
Published: January 2005

AbstractThe thermal isomerization ofcis,anti,cis‐tricyclo[3.1.0.02,4] hexane was used to produce highly vibrationally excited 1,4‐cyclohexadiene. The competition between unimolecular decomposition of the energized diene (to benzene and hydrogen) and collisional stabilization was studied using the parent compound, SF6, CO2, N2, and He as quenching gases. Quenching efficiencies decreased in the order given above. By applying RRKM theory to the isomerization and decomposition reactions, it was possible to calculate the step size in a stepladder model of the deactivation of cyclohexadiene. The step sizes 〈ΔE〉 deduced (at 528 K and in units of kJ/mol) were: parent compound and SF6, 7; CO2, 5; N2, 4; He, 2. The study confirmed the utility of this unimolecular chemical activation system for energy transfer studies.
Intramolecular isotopic effect in the pyrolysis of ethyl‐2d1 chloride
Authors: Papagiannakopoulos P. J. , Benson S. W. 
Published: January 2005

AbstractThe thermal decomposition of deuterated ethyl chloride CH2DCH2Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high‐pressure limit and in the temperature range of 670–1100 K was found to be

The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratio kH/kD was found to decrease with increasing pressure. The RRKM‐theory calculations describe the experimental data well.The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression

when kH and kD are the rate constants for the HCl and DCl channels of elimination.The Arrhenius A factors obtained at the high‐pressure limit together with the temperature‐dependent expression of the branching ratio provided additional experimental data for an assignment (fine‐tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH2DCH2Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the transition‐state model.
A novel wall reaction of OH
Authors: Glass G. P. , Chaturvedi B. K. 
Published: January 2005

AbstractA moderately fast second‐order reaction between OH and atomic hydrogen, which occurred on the halocarbon‐coated or acid‐washed walls of a standard discharge‐flow apparatus, has been investigated using epr spectroscopy. The reaction that occurred in a halocarbon‐coated flowtube was found to be unusual in that it produced a reactive product, namely, atomic oxygen.
Gas‐phase chlorine‐initiated photooxidation of methanol and isopropanol
Authors: Ohta Tomohiro , Bandow Hiroshi , Akimoto Hajime 
Published: January 2005

AbstractThe photolysis of CH3OH/Cl2/air, CH3OH/Cl2/NO2/air, and (CH3)2CHOH/Cl2/NO2/air at 28 ± 2°C was studied using the long‐path FTIR method. The primary reactions of methanol and isopropanol with Cl atoms were α‐hydrogen abstraction (100%), and α hydrogen (85%), and α‐hydrogen abstraction (15%), respectively. The failure to detect hydroxyalkyl‐peroxy nitrates suggested that the oxygen addition to α‐hydroxy radicals is not important. From the product distribution an upper limit of the ratio of oxygen addition to CH2OH and CH3CHOH was estimated to be about 6 and 7%, respectively. The oxygen addition ratio to (CH3)2COH was very low. The reaction mechanism is also discussed.
Nucleophilic character of the tert‐butyl radical. Absolute rate constants for the reactions with substituted toluenes
Authors: Dütsch H. R. , Fischer H. 
Published: January 2005

AbstractThe decay of photochemically generated tert‐butyl radicals is studied at 48°C in 11 m‐ and p‐substituted toluenes by time‐resolved electron spin resonance spectroscopy. It is governed by the second‐order self‐termination perturbed by a pseudo‐first‐order reaction of the radical with the toluenes. The first‐order lifetimes yield the rate constants kA for hydrogen transfer from toluenes to tert‐butyl. Substituent effects on the rate constants confirm the nucleophilic character of the radical.
Base‐catalyzed isomerization of phenylpropenes
Authors: Hassan M. , Nour A. R. O. Abdel , Satti A. M. , Kirollos K. S. 
Published: January 2005

AbstractThe prototropic rearrangement of 3‐phenyl‐1‐propenes to the corresponding 1‐phenyl‐1‐propenes was investigated in basic media utilizing 0.1M sodium ethoxide in absolute ethanol at 81°C. It was found that the effect of substituents on the rate of such isomerizations follows the order: p‐NO2 > o‐Cl > m‐Cl ≥ m‐F > p‐Br > o‐CH3 > m‐CH3 > m‐CH(CH3)2 > p‐CH(CH3)2 ≥ p‐C(CH3)3 > o‐OCH3. This is consistent with first‐order kinetics and “BS” mechanism. Quantitative treatment in terms of Hammett's equation showed a straight line, with a slope (p value) of +2.25. An increase in the strength of the base was also found to cause an increase in the rate of isomerization.
Small effect on the rate of complexation of some dialkyl‐2,2′‐bipyridyl‐5,5′‐dicarboxylates with the ion of Ni(II) in methanol
Authors: A. Dagoberto Pacheco , De O. Francesca Creazzola , B. Jesús A. Sequera , Medina José D. , De Santis De M Vienna 
Published: January 2005

AbstractThe kinetics of formation of the 1:1 complexes of some dialkyl‐2,2′‐bipyridyl‐5,5′‐dicarboxylates with the ion of Ni(II) have been determined by the stopped‐flow spectrophotometric method. Second‐order formation rate constants have been correlated with the Taft modification of the Hammett equation. A linear regression has been found (P = 0.95 confidence) with the following characteristics: slope = ‐0.6 ± 0.1; intercept = 1.32 ± 0.02 (log k0). An inductive effect of the alkyl groups upon the reaction of the complexation is proposed.
The liquid‐phase reaction of CCl3 radicals with primary alcohols
Authors: Feldman Liviu , Alfassi Zeev B. 
Published: January 2005

AbstractThe kinetics of gamma‐radiation‐induced free‐radical reactions in carbon tetrachloride solutions of ethanol and n‐pentanol were studied in the range of 0.05–0.80M and 25–170°C. The rate constant for the reaction

was found as

The activation energy is larger by 0.8 kcal/mol than for secondary alcohols, while the A1 factors are about the same.
High‐temperature kinetics of the reactions of SO2 and SO3 with atomic oxygen
Authors: Smith Owen I. , Tseregounis Spyros , Wang Shie‐Ning 
Published: January 2005

AbstractA nozzle‐beam‐skimmer sampling system is used to measure species concentration profiles for a lean one‐dimensional premixed COO2Ar flame, into which small amounts of sulfur dioxide are introduced. The net formation rate for sulfur trioxide is obtained from the flux fraction profile for this species. The kinetic scheme
equation image

equation image

is then utilized, along with the measured temperature profiles, to evaluate the rate coefficients k1 and k2 over the temperature range of 1435–1850 K. The most satisfactory agreement between the measured net formation rate for SO3 and that calculated on the basis of reactions (1) and (2) is obtained with the rate coefficients

Reactions (1) and (2) are found to be nearly balanced in a substantial region of the flame. Here the data are more sensitive to the difference in activation energies, as opposed to a particular value for either. Implications of this observation on the uncertainty of the deduced temperature dependence for each reaction are discussed, as are some of the procedures used in the data analysis.
The oxidation of diethylhydroxylamine by nitrogen dioxide
Authors: Gleim Jeffrey , Heicklen Julian 
Published: January 2005

AbstractDiethylhydroxylamine, (C2H5)2NOH, was oxidized by NO2 at 25°C in a long‐path‐length infrared gas cell. The measured products of the reaction were HONO and CH3CHO. The reaction scheme which explains the reaction is magnified image was oxidized by NO2, and the reaction was found to be very rapid with k1 > 10−16 cm3/s. The products of the reaction were verified by both infrared absorption (CH3CHO, C2H5NO) and gas chromatography (CH3CHO, NO).