bluuebunny/crossref_metadata_2025_split huggingface dataset:
Triplet excited states of nitronaphthalenes. IV. 1,2‐ and 1,8‐dinitronaphthalenes
Authors: Capellos C. , Suryanarayanan K. 
Published: January 2005

AbstractNanosecond flash photolysis of 1,2‐ and 1,8‐dinitronaphthalenes (1,2‐DNO2N; 1,8‐DNO2N) in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n‐hexane the absorption maxima and lifetimes (1/K) are 490 nm and 1.0 μsec for 1,2‐DNO2N and 550 nm and 2.5 μsec for 1,8‐DNO2N. In deaerated ethanol the corresponding values are 550 nm and 4.3 μsec for 1,2‐DNO2N and 590 nm and 5.3 μsec for 1,8‐DNO2N. The transient absorptions are attributed to the lowest triplet excited states T1 of the 1,2‐ and 1,8‐DNO2N. The observed red shifts in the absorption maxima of the T1 states are indicative of the extent to which electronic charge is transferred intramolecularly during the T1 → Tn transitions. Furthermore, the increased lifetime of the T1 states with increasing solvent polarity indicates the intramolecular charge transfer character of the T1 states. Changes of dipole moments accompanying the T1 → Tn transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the T1 states of 1,2‐ and 1,8‐DNO2N and tributyl tin hydride (Bu3SnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the case of 1,2‐DNO2N. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2‐ and 1,8‐DNO2N behave like n → π* states in nonpolar media while in polar solvents the n → π* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.
High‐temperature pyrolysis of dimethyl ether
Authors: Aronowitz D. , Naegeli D. 
Published: January 2005

AbstractThe kinetics of pyrolysis of dimethyl ether wexre studied in an adiabatic flow reactor at temperatures between 790 and 950°C. The unimolecular rate constant for the initiating step CH3OCH3 = CH3O + CH3 was found to be k1 = 2.16 × 1015e−76,600/RTsec−1. Aspects of the kinetic mechanism are discussed and a system postulated to account for the high‐temperature products.
Vacuum ultraviolet (147 nm) photolysis of 1,2‐fluorochloroethane
Authors: Ichimura T. , Kirk A. W. , Tschuikow‐Roux E. 
Published: January 2005

Abstract1,2‐Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8–20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm−1 · cm−1.The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10−10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbonhalogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.
The oxidation of cerous ions by bromate ions comparison of experimental data with computer calculations
Authors: Barkin S. , Bixon M. , Noyes R. M. , Bar‐Eli K. 
Published: January 2005

AbstractThe oxidation of cerous ions by bromate ions in sulfuric acid medium was followed spectrophotometrically under various experimental conditions. The results were compared to the calculated predictions on the basis of a mechanism suggested by R. M. Noyes and collaborators. The computations were done by solving the complete set of the kinetic differential equations. The results of the computations show that the proposed mechanism explains adequately most of our and previous experimental data. In particular, the mechanism predicts the main features of the reaction, namely, the induction and the fast and slow reaction periods which occur during the oxidation.
On the mechanism of interaction between copper (I) and O2
Authors: Gorbunova N. V. , Purmal A. P. , Skurlatov Yu. I. , Travin S. O. 
Published: January 2005

AbstractThe mechanism of the interaction of Cu+‐α,α‐dipyridyl complex (Cu+L2) with O2 in both neutral and acid media was studied by the stopped‐flow method. The dependence of the mechanism on the acidity of the medium was established. In an acid medium H+ participated in a direct O2 reduction to HO2 by interaction with an oxygen adduct L2Cu+O2 formed without displacement of ligand molecules. In a neutral medium the reaction rate was limited by inner sphere charge transfer from Cu+ to O2 to form an oxygen “charge transfer” complex L2CuO+2. The latter interacted either with the second ion Cu+L2 or with the free ligand, or else it dissociated, reversibly or irreversibly, to form a radical anion O−2. The bimolecular rate constants of the oxygen “adduct” and “charge transfer” complex formation appeared to be kbi = (1.0 ± 0.1) × 105 and (1.5 ± 0.2) × 104M−1ċsec−1, respectively. The effective termolecular rate constants of O2 reduction to HO2 in an acid medium (with contribution from H+) and to O−2 in a neutral medium (with contribution from α,α‐dipyridyl) were kter = 2.7 × 108 and 107M−2ċsec−1. The rate constants of the elementary steps were estimated. The auto‐oxidation mechanism of the aquoion and complexes of Cu+ is discussed in terms of the results obtained.
Very low‐pressure pyrolysis (VLPP) of cyclopentene
Authors: King Keith D. 
Published: January 2005

AbstractThe unimolecularity of the thermal dehydrogenation of cyclopentene has been confirmed using the technique of very low‐pressure pyrolysis (VLPP). Application of RRKM theory shows that the experimental unimolecular rate constants obtained over the temperature range of 942°–1152°K are consistent with the high‐pressure Arrhenius parameters given by

where θ = 2.303 RT kcal/mol. These parameters are in good agreement with static and shock tube studies. No firm evidence could be found for any side reactions or reversibility under the experimental conditions used.
Ene reactions of olefins. I. The addition of ethylene to 2‐butene and the decomposition of 3‐methylpentene‐1
Authors: Richard C. , Scacchi G. , Back M. H. 
Published: January 2005

AbstractThe pyrolysis of ethylene–butene‐2 mixtures has been studied in a static system over the temperature range of 689°‐754°k and for initial pressures of each olefin of 20–200 torr. The two main addition products were cyclopentene and 3‐methylpentene‐1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3‐methylpentene‐1 was formed by the molecular “ene¨︂” addition of ethylene to butene‐2 through a six‐center transition state. The following rate constants were obtained:
equation image
The pyrolysis of 3‐methylpentene‐1 has been studied over the same temperature range and for initial pressures of 20–100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k−1t and k−1c were, however, in reasonable agreement with the measurements of k1t and k1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.
Fre‐radical addition to olefins, Part 22. Arrhenius parameters for the addition of trifluoromethyl radicals to vinyl monomers (CH2CHX)
Authors: Low H. C. , Tedder J. M. , Walton J. C. 
Published: January 2005

AbstractRelative Arrhenius parameters have been determined for the addition of trifluoromethyl radicals to vinyl chloride (XCl), vinyl bromide (XBr), acrylonitrile (XCN), methyl vinyl ketone (XCOCH3), 2‐methylbut‐2‐ene, and to iso‐butene, taking the rate of addition to ethylene as standard. Addition occurred virtually exclusively at the unsubstituted end of all the olefins. The relative rates of addition at 164°C show very little variation. The preexponential terms for addition to the CH2 ends are constant within experimental error, and the small variations in rate are due principally to the activation energy term. The present results are put on an absolute scale using the previously determined Arrhenius parameters for addition to ethylene and are compared with data for other similar monomers determined previously.
The evaluation of rate constants in rate laws containing two terms
Authors: Toby Brian H. , Toby Frina S. , Toby Sidney 
Published: January 2005

AbstractA simple computerized method using APL is described which gives the rate constants for systems obeying the rate law –d[A]/dt = k1[A][B] + k2[A] m [B]l from sets of concentrations and times. Applications are discussed.
HCO radical kinetics: Conjunction of laser photolysis and intracavity dye laser spectroscopy
Authors: Clark J. H. , Moore C. B. , Reilly J. P. 
Published: January 2005

AbstractHCO radical at a concentration of about 1014 cm−3 is produced by monochromatic laser photolysis of H2CO with a 0.6 mJ frequency‐doubled, flashlamp‐pumped dye laser pulse. Intracavity dye laser spectroscopy quantitatively monitors HCO absorbance near 614 nm as a function of delay time between photolysis and probing pulses. Rate constants for HCO + O2 and HCO + NO are found to be 4.0 ± 0.8 × 10−12 and 1.45 ± 0.2 × 10−11 cm3 molecule−1 sec−1.
On the oxidation of malonic acid by ceric ions
Authors: Barkin S. , Bixon M. , Noyes R. M. , Bar‐eli K. 
Published: January 2005

AbstractThe oxidation of malonic acid by ceric ions has been investigated in sulfuric acid solution under a variety of conditions. The initial rate at low ceric ion concentrations is first order in each of the two reactants and has an activation energy of 11.6 kcal/mol; the instantaneous rate constant increases somewhat with time during a single run. At higher concentrations of ceric ion, semilogarithmic plots are sigmoid with a reduced rate constant at long times. The rate decreases slightly with increasing sulfuric acid concentration. Rates of carbon dioxide evolution may be much less than rates of ceric ion reduction because of supersaturation effects. The observations can be explained if dissolved oxygen reacts with organic radicals to catalyze the rate of initial attack on malonic acid, but oxygen must also be consumed irreversibly during these reactions. Computations with plausible rate constants have simulated the experimental observations. These oxygen effects can rationalize peculiar almost discontinuous changes in rate when bromomalonic acid is oxidized by ceric ion. These effects may also explain the previously puzzling observation that some Belousov–Zhabotinsky solutions are oscillatory in bulk but become quiescent but excitable when spread in a thin film in contact with air.
On the decarboxylation of oxalic acid in solutions
Authors: Adams Linda J. , Franzus Boris , Huang Thomas T.‐S. 
Published: January 2005

AbstractThe first‐order kinetics and hydrogen kinetic isotope effect of the decarboxylation of oxalic acid in acetophenone were studied in the temperature range of 109.6°–150.0°C. The rate constants, activation parameters, and hydrogen kinetic isotope effect were calculated. Detailed comparison and discussion of the results were made with the data reported in the literature. Kinetic isotope effects and solvent effects on rates should be considered similar in mechanistic and/or theoretical studies in the sense that kinetic isotope effects result from a small perturbation of the reaction coordinate, while the solvent effect causes a general overall variation on the potential energy surface (thereby resulting in a change in the reaction coordinate).
On the reactivity of diethyl hydroxyl amine toward free radicals
Authors: Abuin E. , Encina M. V. , Diaz S. , Lissi E. A. 
Published: January 2005

AbstractDiethyl hydroxyl amine is an efficient trap for alkyl, alkoxy, and peroxy radicals. The specific rate constant for the reaction of ethyl radicals (gas phase, 25°C), tert‐butoxy radicals (benzene solution, 115°C), and poly (peroxystyryl) peroxy radicals (styrene solution, 50°C) were evaluated as 7.2 × 105, 7.7 × 107, and 2.9 × 105 M−1·sec−1, respectively. Several possible secondary reactions of the nitroxide radicals are discussed.
Kinetics and mechanism of hydrogen–oxygen difluoride reaction in magnesium
Authors: Houser Thomas J. 
Published: January 2005

AbstractThe kinetics of the H2‐OF2 reaction was studied in the temperature range of 160°–310°C at 1 atm total pressure in a magnesium stirred‐flow reactor. Initial concentration ranges were 1/2–1/2 mol·% OF2, 3/16–5 mol·% H2, and 1/4–5.0 mol·% O2; helium was used as the diluent. When the reactants were in a mole ratio of 3/2 (H2/OF2), the rate of disappearance of H2 was 1.5 times that of OF2, consistent with the previously reported stoichiometry. The rate of disappearance of OF2 was strongly influenced by OF2 concentration, weakly influenced by H2 concentration, and inhibited by the oxygen formed in the reaction. An increase in the surface area did not produce a significant change in the rate of reaction. These concentration dependencies led to a proposed ten‐step mechanism from which was derived the following rate equation:

where k0 is a complex combination of elementary rate constants and α and β are elementary rate constants. An Arrhenius treatment of k0 gave

These experimental Arrhenius parameters are lower than those predicted from reported and estimated elementary rate constants. The possibility of heterogeneous contributions is discussed.
A kinetics study of the reactions of OH with several aromatic and olefinic compounds
Authors: Ravishankara A. R. , Wagner S. , Fischer S. , Smith G. , Schiff R. , Watson R. T. , Tesi G. , Davis D. D. 
Published: January 2005

AbstractThe reactions of hydroxyl radicals with eight substituted aromatic hydrocarbons and four olefins were studied utilizing the flash photolysis–resonance fluorescence technique. The rate constants were measured at 298°K using either Ar or He as the diluent gas. The values of the rate constants (k× 1012) in the units of cm3/molec. sec are(a) OH +o‐xylene → products: (12.9±3.8), 20 torr He; (13.0±0.3), 20 torr Ar; (12.4±0.1), 200 torr He;(b) OH +m‐xylene → products: (15.6±1.4), 3 torr Ar; (19.4±0.8), 20 torr Ar; (21.4±0.2), 20 torr He; (20.3±1.9), 200 torr Ar; (20.6±1.3), 200 Torr He;(c) OH +p‐xylene → products: (8.8±1.2), 3 torr Ar; (10.1±1.0), 20 torr He; (10.5±0.6), 200 torr He;(d) OH + ethyl benzene → products: (7.50±0.38), 3 torr He; (7.06±0.26), 20 torr He; (7.95±0.28), 200 torr He;(e) OH +n‐propylbenzene → products: (6.40±0.36), 20 torr He; (5.86±0.16), 200 torr He;(f) OH + isopropylbenzene → products: (7.79±0.40), 200 torr He;(g) OH + hexafluorobenzene → products: (0.221±0.020), 20 torr He; (0.219±0.016) 200 torr He;(h) OH +n‐propyl pentafluorobenzene → products: (2.52±0.54), 3 torr He; (3.01±0.76), 20 torr He; (3.06±0.24), 200 torr He;(i) OH + propylene → products: (25.6±1.2), 20 torr He; (26.3±1.2), 200 torr He;(j) OH + 1‐butene → products: (29.6±1.9), 3 torr He; (29.4±1.4), 20 torr He;(k) OH +cis‐2‐butene → products: (43.2±4.1), 3 torr He; (42.6±2.5), 20 torr He;(l) OH + tetramethylethylene → products: (56.9±1.3), 20 torr He.
Wavelength dependence of the quantum efficiencies of the primary processes in formaldehyde photolysis at 25°C
Authors: Horowitz Abraham , Calvert Jack G. 
Published: January 2005

AbstractThe quantum efficiencies of the primary processes in formaldehyde photolysis (ϕ1 and ϕ2) were determined as a function of wavelength in the range from 2890 to 3380 Å and at 25°C: CH2O + hν → H + HCO (1); CH2O + hν → H2 + CO (2). The estimates of ϕ2 were derived from ΦH2 values obtained in photolyses of CH2O‐isobutene mixtures at high isobutene concentrations where H‐atom scavenging was essentially complete. Values of ϕ1 + ϕ2, obtained from the ΦH2 values from the pure CH2O photolyses, were very near unity at all but the longest wavelengths employed: ΦH2 = ϕ1 + ϕ2 = 1.02 (2930 Å); 1.12 (3130 Å); 1.06 (3150 Å); 1.01 (3250 Å); 1.0 (3335 Å); 0.75 (3380 Å). Our results showed that the onset of photodissociation of CH2O by process (1) was at 3370 ± 10 Å; this corresponds to D(H‐CHO) = 84.8 plusmn; 0.3 kcal/mol. The values of ϕ1 increased regularly with decreasing wavelength from 0 at 3370 Å to ∼0.7 at 3175 Å. Little further variation in ϕ1 occurred from 3175 to 2890 Å. For experiments at λ = 3300 Å, the addition of CO2 (∼300 torr) reduced ϕ2, while the effect on ϕ1 appeared to be small. The present results coupled with the solar irradiance estimates of Peterson [24] and the extinction data for CH2O from McQuigg and Calvert [7] were used to make new estimates of the apparent first‐order rate constants (min−;1 × 103) of process (1) in the lower atmosphere at various solar zenith angles (in parentheses): 2.31 (0°); 2.17 (20°); 1.71 (40°); 0.92 (60°); and 0.17 (78°). The corresponding first‐order rate constants (min−1 × 103) for solar light absorption by CH2O in the lower atmosphere are 7.74 (0°); 7.38 (20°); 6.18 (40°); 3.80 (60°); and 0.96 (78°).
A comparison of two single‐pulse shock‐tube techniques: The thermal decomposition of ethyl chloride and n‐propyl chloride
Authors: Evans P. J. , Ichimura T. , Tschuikow‐Roux E. 
Published: January 2005

AbstractThis investigation presents a detailed examination of the relative reliability of the comparative and absolute rate methods as they are applied to kinetic studies in the single‐pulse shock tube. For this purpose two previously studied reactions, the thermal elimination of HCl from ethyl chloride and n‐propyl chloride, were selected and mixtures of these compounds were shock heated to temperatures in the range of 960°‐1100°K. The experimental results were analyzed by both methods and the rate constants obtained from these analyses are compared with those of previous studies. The advantages and shortcomings of both methods are noted and it is concluded that reliable kinetic data can be obtained by the absolute rate (isolation technique) method with careful examination of the gas‐dynamic flow conditions and taking cognizance of the incident shock deceleration. The limitations of the comparative rate technique encountered in the present study were similar to those detailed in previous investigations.
Unusual H2‐forming chain reaction in the 3130‐Å photolysis of formaldehyde‐oxygen mixtures at 25°C
Authors: Horowitz Abraham , Su Fu , Calvert Jack G. 
Published: January 2005

AbstractA kinetic study has been made of the 3130‐Å photolysis of CH2O (8 torr) in O2‐containing mixtures (0.02–8 torr) and in the presence of added CO2(0–300 torr) at 25°C. Quantum yields of formation of H2, CO, and CO2and the loss of O2were measured. Φand ΦCOwere much above unity. In an explanation of these unexpected results, a new H‐atom‐forming chain mechanism was postulated involving HO2and HO addition to CH2O: CH2O +hν → H + HCO (1) H + CH2O → H2+ HCO (3) H + O2+ M → HO2+ M (6) HCO + O2→ HO2+ CO (8) HO2+ CH2O → (HO2CH2O) → HO + HCO2H (15) HO + CH2O → H2O + HCO† (16); HCO† → H + CO (19) HO + CH2O → H2O + HCO (17) and HO + CH2O → HCO2H + H (18). When the results are rationalized in terms of this mechanism, the data suggestk16≫k17andk16/k18≅ 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO2H formation was used as a monitor of the rate of reaction (7) HCO + O2+ M → HCOO2+ M (7). The present data from experiments atP= 8 torr andP= 1–4 torr givek7[M]/(k7[M] +k8) ≥ 0.049 ± 0.017. These data coupled with thek8estimates of Washida and coworkers givek7≥ (4.4 ± 1.6) × 1011l2/mol2·sec for M = CH2O. The reaction sequence proposed here is consistent with the observed deterimental effect of O2addition on the laser‐induced isotope enrichment in HDCO. In additional studies of CH2O‐O2‐isobutene mixtures it was found that Φwas equal to ϕ2as estimated in O2‐free CH2O‐isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O2addition in CH2O photolysis does not result from perturbations in the fragmentation pattern of the excited CH2O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O2→ HO2+ CO (ν = 1).
Mechanistic details of the Belousov–Zhabotinsky oscillations. II. The organic reaction subset
Authors: Edelson D. , Noyes R. M. , Field R. J. 
Published: January 2005

AbstractOur previous mechanistic model for the Belousov–Zhabotinsky reaction has been revised to include a more realistic set of reactions for the oxidation pathways of the organic intermediates. A few other rate constants have also been modified to include new information. The revised mechanism reproduces the essential experimental observations, although the periods of oscillation are somewhat too long and oscillations cease at malonic acid concentrations about ten times greater than the observed lower limit. However, the essential features of the mechanism are clearly understood.
A kinetics study of the temperature dependence of the reactions of OH(2Π) with CF3CHCl2, CF3CHClF, and CF2ClCH2Cl
Authors: Watson R. T. , Ravishankara A. R. , Machado G. , Wagner S. , Davis D. D. 
Published: January 2005

AbstractThe flash photolysis resonance fluorescence technique has been utilized to determine the rate constants for three reactions involving the hydroxyl radical [OH(2≅)] and three halogenated C2 alkanes. The nominal temperature range covered was 250–375 K. The compounds studied and the resulting Arrhenius expressions in units of cm3/molec·sec are
equation image
The error limits in these expressions are such that they include any possible systematic errors due to the presence of impurities in the halocarbon samples. Tropospheric lifetimes have been calculated for the above species by combining the above rate constant data with global seasonally and diurnally averaged hydroxyl radical concentrations.
Radical equilibrium studies. II. The thermodynamic parameters of s−butyl
Authors: Marshall Roger M. , Page Nicholas D. 
Published: January 2005

AbstractThe thermal decomposition of azomethane in the presence of propene has been investigated in the range of 568–638°K at reactant partial pressures of up to about 7 torr in the presence of at least 170 torr of argon. The elementary reactions taking place in such conditions are discussed in detail. It is shown that a situation approaching equilibrium is attained between the processes
equation image
Values are obtained for the equilibrium constant K2, which can be described by the equation

Using the best available thermodynamic parameters for methyl and propene, it is concluded that those for s−butyl are in need of adjustment. We recommend the values ΔHf0 (300°K) = 13.8 ± 1.0 kcal/mol and S3000 (1 atm standard state) = 75.6 ± 3.0 cal/mol°K together with group additivity values of the heat capacity. A comparison of measured values of K2 with values calculated from independent measurements of k2 and k−2 shows a discrepancy of about a factor of 3.5.
The kinetics and mechanism of n‐butyraldehyde photolysis in the vapor phase at 313 nm
Authors: Förgeteg S. , Bérces T. , Dóbé S. 
Published: January 2005

AbstractThe photolysis was investigated at 313 nm wavelength, 253–529 K temperatures, and 4 × 10−11‐2 × 10−9 mol·photon/cm2·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.