bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of HTO formation in gaseous tritium mixtures
Authors: Papagiannakopoulos P. J. , Easterly C. E. 
Published: January 2005

AbstractThe mechanisms for the conversion of molecular tritium gas to tritiated water are examined for tritium mixtures with (1) oxygen and nitrogen, (2) oxygen and argon, and (3) water and helium, for which previous experimental data exist. By analyzing results of these experiments in light of the radiation chemistry involved in a mixture of tritium and other gases, an understanding of the conversion mechanisms is reached. The formation of H and/or OH free radicals as intermediate species is of particular significance in the formation of HTO in that these radicals initiate a number of reactions which lead to the formation of water. These reactions are analyzed in terms of steady‐state kinetics to obtain predictive models which can be judged against the experimental observations. For the three experimentally observed mixtures, model agreement is found to be within a factor of 2–3.
Chemistry in mixtures of Kr with Ar and He illuminated with Kr resonance radiation
Authors: Young Robert A. 
Published: January 2005

AbstractThe formation and destruction of excited rare‐gas dimers have been studied using resonance optical excitation of high‐pressure gas mixtures containing Kr. From an analysis of the resulting emission, 19 reaction rate coefficients have been inferred. It is concluded that atom–atom interchange processes play a major role in rare‐gas eximer formation, and that stepwise relaxation down the eximer vibrational ladder is less important than multistep relaxation due to atom–atom exchange in the excited eximer.
Gas‐phase thermolysis of sulfur compounds. Part III: n‐butyl 2‐propenyl sulfide
Authors: Martin Gonzalo , Drayer Alberto , Ropero Marcos , Alonso Miguel E. 
Published: January 2005

AbstractThe pyrolysis of n‐butyl 2‐propenyl sulfide has been investigated in a static system in the initial pressure range of 50–350 torr. The reaction was found to be homogeneous and first order. The rate coefficients are given by the Arrhenius equation

between 262 and 293°C. The rate of the reaction remains unchanged in the presence of cyclohexene as radical inhibitor. The main reaction products were propene and a trimer of n‐butyl thioaldehyde. The results are interpreted in terms of a molecular mechanism involving a cyclic six‐centered transition state. This mechanism is supported by the pyrolysis of 1,1‐dideutero‐n‐butyl 2‐propenyl sulfide at 281°C. The kinetic deuterium isotope effect had a value of 2.7 ± 0.2. Nuclear magnetic resonance and mass spectroscopic analysis of the reaction products showed the deuterium to be distributed as expected from the proposed reaction mechanism.
Kinetics and energetics of the criegee intermediate in the gas phase. I. The criegee intermediate in ozone–alkene reactions
Authors: Herron John T. , Martinez Richard I. , Huie Robert E. 
Published: January 2005

AbstractThe chemistry and energetics of the Criegee intermediate, a primary product of the ozonolysis of alkenes, are discussed in terms of recent ab‐initio calculations and laboratory studies. The experimental observations in O3–alkene systems can be rationalized on the basis of a general mechanism: magnified image where the ‡ represents the range of internal excitation energies available to the planar dioxymethylenes (i.e., the Criegee intermediates) initially formed via exothermic O3‐alkene reactions. Estimates are given for the rate constants of these reactions, and a critique is provided of the possible role of the Criegee intermediate and its isomers in the formation of alkanoic acid anhydrides in O3–alkene systems and in the formation of H2SO4 aerosols in O3–alkene–SO2 systems.
The mechanism of O3‐aldehyde reactions
Authors: Martinez Richard I. 
Published: January 2005

AbstractA new mechanism is proposed for gas‐phase O3‐aldehyde reactions. Certain aspects of the new mechanism may be applicable also to O3‐aldehyde reactions in solution. The proposed mechanism involves initiation by addition of O3 across the aldehydic CO bond. The initiation process and the subsequent chemistry together represent an exact analogue of the Criegee mechanism for O3‐alkene reactions.
Shock‐initiated decomposition of tetramethylgermane and the reaction of methyl radicals with toluene
Authors: Dzarnoski J. , Ring M. A. , O'Neal H. E. 
Published: January 2005

AbstractThe shock‐initiated decomposition of tetramethylgermane (1078–1242 K) has been found to involve successive elimination of methyl radicals with the rate constant k1 for the first step given by

In the presence of excess toluene the products were CH4 (major), C2H4, and C2H6. Results relevant to the reaction of methyl radicals with toluene compared to methyl radical recombination are discussed.
Study of ethylene oligomerization
Authors: Ács G. , Péter A. , Huhn P. 
Published: January 2005

AbstractA study was made of the oligomerization of ethylene, initiated by the thermal decomposition of azoethane and azo‐isopropane at low temperatures, where the polymerization equilibria are shifted somewhat in the direction of the formation of products with longer carbon chains. The findings supported the picture acquired from a study of the propionaldehyde–ethylene system. Also under these conditions the oligomerization proceeds via addition between the ethylene and radicals, followed by isomerization and decomposition of the longer radicals, with a tendency to yield propylene and longer olefins. At the lower temperatures the decomposition of radicals with shorter carbon chain becomes less important in comparison with their addition reactions and, in spite of the otherwise identical mechanism, this leads to a different product distribution.
Reaction of hydrogen atoms and O2(1Δg)
Authors: Cupitt L. T. , Takacs G. A. , Glass G. P. 
Published: January 2005

AbstractThe reaction of atomic hydrogen with O2(1Δg) has been investigated as a function of temperature, using a fast discharge‐flow apparatus equipped for EPR detection of free radical species. The rate constant for the overall reaction was measured as (1.46 ± 0.49) × 10−11 exp(‐4000 ± 200 cal/mol/RT) cm3/s. Evidence is presented which suggests that the reaction occurs principally via abstraction, H + O2(1Δg) → OH + O, rather than via physical quenching, H + O2(1Δg) → H + O2(X3Σg−).
Rate constants for the reaction of OH radicals with a series of alkanes and alkenes at 299 ± 2 K
Authors: Atkinson Roger , Aschmann Sara M. , Winer Arthur M. , Pitts James N. 
Published: January 2005

AbstractUsing methyl nitrite photolysis in air as a source of hydroxyl radicals, relative rate constants for the reaction of OH radicals with a series of alkanes and alkenes have been determined at 299 ± 2 K. The rate constant ratios obtained are: relative to n‐hexane = 1.00, neopentane 0.135 ± 0.007, n‐butane 0.453 ± 0.007, cyclohexane 1.32 ± 0.04; relative to cyclohexane = 1.00, n‐butane 0.341 ± 0.002, cyclopentane 0.704 ± 0.007, 2,3‐dimethylbutane 0.827 ± 0.004, ethene 1.12 ± 0.05; relative to propene = 1.00, 2‐methyl‐2‐butene 3.43 ± 0.13, isoprene 3.81 ± 0.17, 2,3‐dimethyl‐2‐butene 4.28 ± 0.21. These relative rate constants are placed on an absolute basis using previous absolute rate constant data and are compared and discussed with literature data.
Differential method for the determination of the order of reaction and the rate constants
Authors: Ross S. D. 
Published: January 2005

AbstractA method is proposed whereby the orders and rate constants for processes obeying the rate law −dA/dt = kAn may be determined. The method is illustrated in two ways. First, simulated data for processes of various orders are treated, and the treatment is shown to be capable of reproducing orders and rate constants to a high degree of accuracy. The factors affecting the accuracy with which n and k can be determined are considered. These are inaccuracy in the determination of concentration values, irregularity of the time intevals between concentration determinations, and the length of those time intervals. It is shown that if concentrations are determined at times that are close together, the effect of the other two factors is small, but if the time intervals are made longer, the errors due to the other two factors affect the calculated values of n and k much more seriously. Second, the method was applied to two homogeneous reactions, of which one was first‐order and one was second order, and three heterogeneous reactions, of which one was found by the original workers to be first order, one to be zero order, and one to vary between zero and first order, depending on the initial pressure. The present method gives results in agreement with these conclusions and reproduces the rate constants to within ±5% in all cases.
Quantized RRK theory of unimolecular reaction rates
Authors: Schranz Harold W. , Nordholm Sture , Hamer Norman D. 
Published: January 2005

AbstractThe main difference between the simple RRK theory and the better based but more complex RRKM theory is explained. Starting from the premise that the classical versus quantum mechanical estimation of the density of states is the major source of the difference, earlier attempts to incorporate the quantum effects in an effective value for the number of oscillators s are noted. By examining the expression for the RRKM rate coefficient it is found that a single effective s value will generally not suffice, but a much better representation of the quantum effects can be obtained if it is recognized that the problem inherently contains two different effective s values. A theory based on this analysis is constructed. It reproduces RRKM results to much improved accuracy, removing difficulties found earlier with single‐s‐value theories.
Temperature dependence of the rate constant for the reaction OH + H2S
Authors: Lin C. L. 
Published: January 2005

AbstractAbsolute rate constants for the reaction of OH with H2S have been measured over the temperature range of 239–425 K using the flash photolysis–resonance fluorescence technique. The results showed that the rate constants deviate slightly from Arrhenius behavior but can still be represented adequately by the following Arrhenius equation:

Comparisons with recent literature values are presented.
Laser magnetic resonance spectroscopy of ClO and kinetic studies of the reactions of ClO with NO and NO2
Authors: Lee Yuan‐Pern , Stimpfle Richard M. , Perry Robert A. , Mucha John A. , Evenson Kenneth M. , Jennings Donald A. , Howard Carleton J. 
Published: January 2005

AbstractFar‐infrared rotational transitions in ClO(X2∏3/2, υ = 0) have been observed using laser magnetic resonance (LMR) with an optically pumped spectrometer. Five observed transitions at wavelengths between 444 and 713 µm have been compared with values predicted with spectroscopic constants from the literature. LMR detection of ClO has been used to study its reactions with NO and NO2 in a discharge flow system under pseudo‐first‐order conditions for ClO. The measured rate constants are k(ClO + NO) = (7.1 ± 1.4) × 10−12 exp[(270 ± 50)/T] cm3/molec·s for the temperature range of 202 < T < 393 K; k(ClO + NO2 + M) = (2.8 ± 0.6) × 10−33 exp[(1090 ± 80)/T] cm6/molec2·s (M = He, 250 < T < 387 K), (3.5 ± 0.6) × 10−33 exp[(1180 ± 80)/T] (M = O2, 250 < T < 416 K), and (2.09 ± 0.3) × 10−31 (M = N2, T = 297 K). All measurements were made at low pressures, between 0.6 and 6.6 torr. These results are compared with those from other studies.
Oscillatory behavior during the oxygen oxidation of ascorbic acid
Authors: Young Jack , Franzus Boris , Huang Thomas T.‐S. 
Published: January 2005

AbstractThe oscillatory phenomenon was observed in aqueous solution during the oxidation of ascorbic acid by oxygen. Even though the exact number and amplitude of the oscillations could not be exactly duplicated for each and every run, such factors as temperature, concentration of ascorbic acid, cupric ions, and pH affecting the oscillatory behavior were studied, and those regions where oscillations occurred were delineated. A mechanism consistent with the oscillatory behavior is proposed and discussed.
New aspects of the mechanism for the thermal hydrocracking of indan and tetralin
Authors: Penninger Johannes M. L. 
Published: January 2005

AbstractThermal cracking of indan and tetralin in the gas phase was carried out in a flow reactor at 500°C and 8 MPa pressure in the presence of hydrogen and nitrogen. The primary reactions are ring cracking and dehydrogenation, regardless of the nature of the second component. Ring cracking, however, is strongly enhanced by the presence of hydrogen. This enhancement becomes less significant with increasing concentration of the hydrocarbon in the gaseous reaction mixture and also with a decreasing ratio of hydrogen to hydrocarbon. At hydrocarbon concentrations larger than approximately 0.5 g·mol/L and H2‐to‐HC molar ratios of 1 or lower, conversion rates are almost equal in hydrogen and in nitrogen. Ring cracking exhibits different kinetic behavior in nitrogen than in excess of hydrogen. This illustrates the occurrence of two complementary cracking mechanisms, each of which can dominate in certain concentration ranges. The H2‐initiated ring cracking is gradually transformed into a hydrogen‐donor mechanism as the leading reaction scheme when the concentration of indan or tetralin is increased.
A dual‐frequency Belousov Zhabotinskii oscillating reaction with ethyl acetoacetate as organic substrate
Authors: Salter Leo F. , Sheppard John G. 
Published: January 2005

AbstractThe experimental behavior of the cerium‐ and manganese‐catalyzed Belousov Zhabotinskii oscillating reaction with ethyl acetoacetate as organic substrate has been investigated. Under certain conditions the system displays two types of temporal oscillations. Damped highfrequency oscillations appear immediately after the addition of potassium bromate solution to complete the reaction mixture. These high‐frequency oscillations may be regarded as being superimposed on an induction period of the type found in the reaction using malonic acid. After the induction period, low‐frequency oscillations of the normal type are obtained. Both the high‐frequency and the low‐frequency oscillations can be monitored with a platinum redox or with a bromide specific ion electrode.
Kinetics and mechanism of base‐catalyzed cleavage of some bicyclo[4.2.0.]octa‐1,3,5‐trien‐7‐one (benzocyclobuten‐1(2H)‐one) derivatives
Authors: Sorial Mary A. , Iskander George M. , Bolton R. 
Published: January 2005

AbstractThe kinetics of cleavage of 3‐hydroxybicyclo[4.2.0]octa‐1,3,5‐trien‐7‐ones in aqueous sodium hydroxide, and of the alkoxy and acetoxy analogues in methanolic sodium methoxide solution, were examined under pseudo‐first‐order reaction conditions. The dependence of the rate upon the basicity of the solvent, whether measured by H− or by [OR−], reflects the possible structure of the transition state. The deduced mechanism is also supported by the effects of substituents upon the reaction rate. The relative amounts of the volatile reaction products derived from o‐toluic acid and from phenylacetic acid are understood in terms of the substituent effect upon the relative stabilities of the carbanions.
Ozone–isoprene reactions: Product formation and aerosol potential
Authors: Kamens R. M. , Gery M. W. , Jeffries H. E. , Jackson M. , Cole E. I. 
Published: January 2005

AbstractDark‐phase experiments between isoprene and O3 are discussed. UNC outdoor chamber experiments have shown that in high‐concentration systems of isoprene and O3 (5 ppm C and 1 ppm) approximately 75% of the reacted carbon can be observed in the product formation of HCHO, CO, methacrolein, methylvinylketone, methylglyoxal, acetaldehyde, and propylene. Mechanisms were developed which gave reasonable fits to dark‐phase chamber experiments of MACR, MVK, isoprene, and O3. Experimental data and modeling results were used to generate O3 rates of attack on MVK and MACR. An isoprene–O3 rate of 1.67 × 10−2 ppm−1·min−1 was used and is consistent with other rates reported in the literature. Dark isoprene–O3 systems appear to form homogeneously nucleated aerosol. Most of these particles appear and remain at diameters well below the optical cutoff region (0.3–0.5 μm), as opposed to the particles from similar α‐pinene–O3 systems, which also form at smaller sizes but then grow into the optical size range (0.5 μm). Lower concentrations of α‐pinene and O3 (0.2 ppm C and 0.12 ppm) still generated substantial aerosol, but by comparison, rapid CN nucleation was not observed during a similar side‐by‐side system of isoprene and O3.
Self‐ and cross‐disproportionation‐to‐combination rations for cyclopentyl and cyclohexyl radicals and their deuterated analogues
Authors: Fujisaki Noboru , Gäumann Tino 
Published: January 2005

AbstractHydrogen, cycloalkene, and bicycloalkyl were found to be the principal products which account for ≈︁97% of all products formed in the gas‐phase radiolysis of water vapor containing low concentrations of cycloalkanes. From the ratios of cycloalkene‐to‐bicycloalkyl yields extrapolated to the zero dose, the self‐ and cross‐disproportionation‐to‐recombination rate constant ratios Δ = kd/kc were determined for the following 12 reactions: Δ(c‐C5H9, c‐C5H9) = 0.73; Δ(c‐C5D9, c‐C5D9) = 0.58; Δ(c‐C6H11, cC6H11) = 0.59; Δ(c‐C6D11, c‐C6D11) = 0.46; Δ(c‐C5H9, c‐C6H11) = 0.28; Δ(c‐C5D9, c‐C6H11) = 0.28; Δ(c‐C5H9, c‐C6D11) = 0.24; Δ(c‐C5D9, c‐C6D11) = 0.24; Δ(c‐C6H11, c‐C5H9) = 0.33; Δ(c‐C6H11, c‐C5D9) = 0.25; Δ(c‐C6D11, c‐C5H9) = 0.35; and Δ(c‐C6D11, c‐C5D9) = 0.28, where in the case of the cross‐disproportionation the symbol Δ(R1,R2) is used to represent kd/kc for the disproportionation in which radical R1 captures a hydrogen (deuterium) atom from radial R2. The geometrical mean rule holds in the cross‐combination reactions of cyclopentyl and cyclohexyl radicals. The kinetic isotope effect in the disproportionation reaction was determined as 1.24 ± 0.06.
Spectra of propylperoxy radicals and rate constants for mutual interaction
Authors: Adachi Hiroyuki , Basco Norman 
Published: January 2005

AbstractThe flash photolyses of azo‐n‐propane and azoisopropane in the presence of oxygen have been studied by kinetic spectroscopy. The transient absorption spectra observed in the region of 210–290 nm are assigned to the n‐propylperoxy and isopropylperoxy radicals. For the n‐propylperoxy radical, εmax = 1148 ± 29 L/mol cm at 242.5 nm and for the isopropylperoxy radical, εmax = 1273 ± 75 L/mol cm at 240 nm. The rate constants for the mutual reactions (7) 2RO2· → products were measured to be k7 = (2.0 ± 0.2) X 108 L/mol s for the n‐propylperoxy radical and k7 = (7.8 ± 2.2) X 105 L/mol s for the isopropylperoxy radical.
A flash photolysis resonance fluorescence investigation of the reaction OH + H2O2 → HO2 + H2O
Authors: Kurylo Michael J. , Murphy Jennifer L. , Haller Geoffrey S. , Cornett Kenneth D. 
Published: January 2005

AbstractThe flash photolysis resonance fluorescence technique has been used to measure the rate constant for the reaction
equation image
over the temperature range of 250–370 K. The present results are in excellent agreement with three very recent studies, and the combined data set can been used to derive the expression
equation image
similar to that currently used in atmospheric modeling applications.A summary of our computer simulation of this reaction system is presented. The results of the computations indicate the absence of secondary reaction complications in the present work while revealing significant problems in the earlier (pre‐1980) studies of the title reaction.
An ftir study of the reaction between nitrogen dioxide and alcohols
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P. 
Published: January 2005

AbstractThe reaction 2NO2 + ROH = RONO + HNO3 (R = CH3 or C2H5) has been studied using the FTIR method at reactant pressures from 0.1 to 1.0 torr at 25°C. The termolecular rate constant for the forward reaction was determined to be (5.7 ± 0.6) × 10−37 cm6/molec2·s for CH3OH and (5.7 ± 0.8) × 10−37 cm6/molec2·s for C2H5OH, that is, d[RONO]/dt = k[NO2]2[ROH]. The corresponding equilibrium constants were measured as 1.36 ± 0.06 and 0.550 ± 0.025 torr−1, respectively. These results are consistent with those of a previous study based on the NO2 decay measurements at reactant pressures from 1 to 10 torr.
Mechanism of the pyrolysis of C2HCl5, molecular and radical steps
Authors: Benson Sidney W. , Weissman Maia 
Published: January 2005

AbstractAn analysis of the thermochemistry of the kinetic parameters of the elementary reactions involved in the pyrolysis of pentachloroethane has resolved several disputed, unclarified, or inconsistent aspects of the reaction mechanism. The resulting mechanisms for the inhibited and uninhibited pyrolysis account for all reported experimental findings. On the basis of this interpretation, first experimentally based values have been derived for the following: DH0(CCl3–CHCl2) = 79.0 ± 1.0 kcal/mol, ΔH(CHCl2) = 25.7 ± 1.0 kcal/mol, and E1 = 59.7 ± 1.0 kcal/mol C2HCl5 magnified image.
Mechanism of oxidation of triphenylphosphine, triphenylarsine, and triphenylstibine by potassium peroxodisulfate
Authors: Srinivasan C. , Pitchumani K. 
Published: January 2005

AbstractThe kinetics of oxidation of triphenyl derivatives of group V elements Ph3M (M = P, As, Sb) by potassium peroxodisulfate have been investigated spectrophotometrically in 60% acetonitrile–40% water (v/v) mixture. The reaction follows second‐order kinetics, first order in each reactant. Changes in the [H+] and ionic strength have negligible effect on the reaction rate. Addition of acrylonitrile fails to inhibit the rate. The results indicate a rate‐determining nucleophilic displacement of the Ph3M molecule on the peroxide linkage. The relative rate order has been found to be Ph3P > Ph3Sb > Ph3As. This can be attributed to two conflicting trends.
Acid‐catalyzed hydrolysis of some diazoacetophenones in aqueous dioxan
Authors: Thomas C. W. , Leveson L. L. 
Published: January 2005

AbstractRate constants and activation parameters for the acid‐catalyzed hydrolysis of eight ring‐substituted diazoacetophenones have been measured in three dioxan–water mixtures. An isokinetic relationship applies to the results obtained using a 50% dioxan–water mixture as solvent. Solvent and substituent effects are discussed together with some mechanistic aspects. Substituent constants are reported for the COCHN2 group.
Rate constants for the gas‐phase reactions of OH radicals with a series of bi‐ and tricycloalkanes at 299 ± 2 K: Effects of ring strain
Authors: Atkinson Roger , Aschmann Sara M. , Carter William P. L. 
Published: January 2005

AbstractRelative rate constants for the gas‐phase reactions of OH radicals with a series of bi‐ and tricyclic alkanes have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3/molec·s, the rate constants obtained are (× 1012 cm3/molec·s): bicyclo[2.2.1]heptane, 5.53 ± 0.15; bicyclo[2.2.2]octane, 14.8 ± 1.0; bicyclo[3.3.0]octane, 11.1 ± 0.6; cis‐bicyclo[4.3.0]nonane, 17.3 ± 1.3; trans‐bicyclo[4.3.0]nonane, 17.8 ± 1.3; cis‐bicyclo[4.4.0]decane, 20.1 ± 1.4; trans‐bicyclo[4.4.0]decane, 20.6 ± 1.2; tricyclo[5.2.1.02,6]decane, 11.4 ± 0.4; and tricyclo[3.3.1.13,7]decane, 23.2 ± 2.1. These data show that overall ring strain energies of ≲4–5 kcal mol−1 have no significant effect on the rate constants, but that larger ring strain results in the rate constants being decreased, relative to those expected for the strain‐free molecules, by ratios which increase approximately exponentially with the overall ring strain.