bluuebunny/crossref_metadata_2025 huggingface dataset:
The triplet state of 4‐nitronaphthylamine
Authors: Capellos C. , Lang F.
Published: January 2005

Nanosecond spectroscopic and kinetic studies of 4‐nitronaphthylamine (4‐NO2NA) in aerated and deaerated nonpolar solvents at room temperature show a transient species with absorption maxima at 470 and 665 nm. The rate constant for the decay of this species in deaerated benzene is 6.7 × 105 sec−1, while in aerated benzene solutions the species is quenched by oxygen with arate constant k = 2.0 × 109M−1·sec−1. The transient absorption at 470and 665 nm is assigned to the lowest triplet excited state of 4‐NO2NA. In polar solvents, however, electronic excitation of 4‐NO2NA does not lead to any detectable transient absorption between 400 and 800 nm for the temperature range of 25 to −150°C. This is attributed to lack of intersystem crossing of 4‐NO2NA in polar solvents.
BEBO Calculations for hydrogen abstraction by 0(3P)
Authors: Previtali Carlos M. , Neumann Miguel G.
Published: January 2005

Rate constants for hydrogen transfer reactions from C—H bonds to O(3P) in the gas phase have been calculated by the bond‐energy bond‐order method. The use of a single or double triplet repulsion term is discussed. Computational results indicate that with carefully selected input parameters, it is unnecessary to use a double‐repulsion term. Tunneling corrections were carried out by two different procedures. Results indicate that in this case there is not much difference between the simple Wigner's treatment and more complicated methods.
The gas‐phase pyrolysis of alkyl nitrites. IV. Ethyl nitrite
Authors: Batt L. , Milne R. T.
Published: January 2005

The rate of decomposition of ethyl nitrite (EN) has been studied in a static system over the temperature range of 162‐218°C. The main products are formaldehyde, acetaldehyde, ethanol, and nitrous oxide. For low concentrations of EN (10−5‐10−4M), but with a high total pressure of CF4 (∼0.9 atm) and small extents of reaction (2‐6%), the first‐order homogeneous rates of CH2O formation are a direct measure of reaction (1), since k3bk2(NO):
equation image
Addition of large amounts of NO(∼0.9 atm) completely suppressed CH2O formation in agreement with the observed value for k3b.

The rate of reaction (1) is given by k1 = 1016.0‐41.8/θ−1. Since (E1 + RT) and ΔH±1 are identical, both may be equated with D(EtO‐NO) = 42.4 ± 0.9 kcal/mol and E2 = O± 1 kcal/mol. The thermochemistry leads to the result ΔHDelta;f(EN) = ‐24.5 ± 1 kcal/mol. From ΔS1 and A1, k2 is calculated to be 1010.3M−1θ−1. From an independent observation that k6/k2 = 0.3 ± 0.05 independent of temperature

it is concluded that k6 = 109.8M−1Δ−1.

The addition of NO has no effect on the AcH yields. Although the yields of AcH are affected by the surface‐to‐volume ratio of different reaction vessels, it is concluded that in a spherical reaction vessel, the AcH arises as the result of an essentially homogeneous elimination of HNO from EN(5):

and reaction (6). The rate of AcH formation is given by kobs = 1013.7‐37.5/θ−1. By using isobutane (t‐BuH) as a radical trap for EtO (4),

a value for k3b was determined to be 1015.0‐21.6/θ s−1.

From an independent observation that k2:k2:k6:k6 was 1: 0.4: 0.3: 0.18
equation image
we find k2θ = 109.9M−1→ s−1, k1θ = 1016.0‐40.0/θ s−1, and k6± = 109.6M−1 · s−1.
Fast kinetic studies of chemical reactions using high‐intensity pulse radiolysis reaction of hydrogen peroxide with pentavalent vanadium
Authors: Pucheault J. , Ferradini C. , Gardes M. , Lesigne B. , Gilles L. , Muller J. C.
Published: January 2005

High‐intensity pulse radiolysis, using a Febetron, has made it possible to obtain in a few microseconds homogeneous H2O2 concentrations of about 10−4 to 10−3M without any other reactive radiolytical product. The kinetics of the reaction of this H2O2 with a solute have been studied as a function of time for periods ranging from tens of microseconds to tens of milliseconds.

An analytical model of this method is presented and then compared with the results of experiments in which the H2O2 concentrations are measured. The rate constant for the peroxidation of pentavalent vanadium is determined to be k = (5.7 ± 0.5) × 103M−1 plusmn; s−1.
Esterification of alcohols with acetic acid over ferric oxide
Authors: Kuriacose J. C. , Jewur S. S.
Published: January 2005

Ferric oxide has been found to promote both the ketonization of acetic acid and its esterification with methyl alcohol, isopropyl alcohol, and benzyl alcohol. The competitive kinetic technique, where the esterification reaction is made to compete with the ketonization of acetic acid, has been used to elucidate the mechanistic model for the ketonization of acetic acid on iron oxide. The ketonization of acetic acid at 375°C is found to be a second‐order reaction which proceeds through a Langmuir‐Hinshelwood mechanism.
Hydrogen abstraction from trichlorosilane by the trichloromethyl and 1,1‐dichlorotrifluoroethyl radicals
Authors: Ormson B. N. , Perrymore W. D. , White M. L.
Published: January 2005

The Arrhenius parameters for the reactions
equation image
and
equation image
have been measured. Reaction (2a) was generated and studied by the photolysis of tetrachloromethane in the presence of trichlorosilane and reaction(2b) by the photolysis of 1,1,1,‐trichlorotrifluoroethane in the presence of trichlorosilane.

The measured data are given by the expressions

.
Asymptotic quantum yield of triplet sensitized decomposition
Authors: Oref I.
Published: January 2005

The asymptotic quantum yield of triplet energy transfer is found by calculating the fraction of acceptor molecules with energy above the minimum energy for decomposition. This is done by allowing for a statistical energy distribution among the internal modes in the collision complex. It is found that for a monatomic triplet donor most of the triplet energy is transferred to the acceptor molecule, while for a polyatomic donor molecule only a fraction of it is available for future decomposition of the acceptor.
Thermal decomposition of perfluoro‐di‐t‐butyl peroxide
Authors: Ireton R. , Gordon A. S. , Tardy D. C.
Published: January 2005

The thermal decomposition of perfluoro‐di‐t‐butyl peroxide has been studied for the first time. The reaction was carried out in the gas phase between 5 and 600 torr in the 108‐149°C temperature region. The products consisted solely of C2F6 and CF3COCF3. The decomposition was found to be first order and homogeneous. The rate constant is given by log kdecomp(sec−1) = (16.2 ± 1.2) ‐ (148.7 4.4)/2.3RT where R is 0.008314kJ/mol · °K. These Arrhenius parameters are consistent with those determined for the decomposition of di‐t‐butyl peroxide.
The NO‐ and NO2‐catalyzed decomposition of I2 in shock waves
Authors: Hippler H. , Luther K. , Teitelbaum H. , Troe J.
Published: January 2005

Measurements of the NO‐catalyzed dissociation of I2 in Ar in incident shock waves were carried out in the temperature range of 700°‐1520°K and at total concentrations of 5 × 10−6‐6 × 10−5 mol/cm3, using ultraviolet‐visible absorption techniques to monitor the disappearance of I2. It was shown that the main reaction responsible for the disappearance under these conditions is I2 + NO → INO + I, for which a rate coefficient of (2.9 ± 0.5) × 1013 exp[‐(18.0 ± 0.6 kcal/mol)/RT] cm2/mol·sec was determined. The INO formed dissociates rapidly in a subsequent reaction. The reaction, therefore, constitutes a “chemical model” for a “thermal collisional release mechanism.” Preliminary measurements of the rate coefficient for I2 + NO2 → INO2 + I are also presented. Combined with information on the reverse reactions obtained in earlier room temperature experiments, these results lead to accurate values of ΔH°f for INO and INO2 equal to 29.7 ± 0.5 and 15.9 ± 1 kcal/mol, respectively.
Kinetics of the reaction Cl + CH4 → CH3+ HCl from 200° to 500deg;K
Authors: Zahniser Mark S. , Berquist Bruce M. , Kaufman Frederick
Published: January 2005

The rate constant for the reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Cl} + {\rm CH}_4 \mathop {\longrightarrow}\limits^1 {\rm CH}_3 + {\rm HCl}$\end{document} has been determined over the temperature range of 200°–500°K using a discharge flow system with resonance fluorescence detection of atomic chlorine under conditions of large excess CH4. For 300° > T > 200°K the data are best fitted to the expression k1 = (8.2 ± 0.6) × 10−12 exp[−(1320 ± 20)/T] cm3/sec. Curvature is observed in the Arrhenius plot such that the effective activation energy increases from 2.6 kcal/mol at 200° < T < 300°K to 3.5 kcal/mol at 360° < T < 500°K. The data over the entire range may be fitted by the expression k1 = 8.6×10−18 T2.11 exp[−795/T]. These results are compared with other experimental studies and with a semiempirical transition state calculation. Their atmospheric significance is discussed.
Temperature dependence of the reactions of HO2 with NO and NO2
Authors: Simonaitis R. , Heicklen Julian
Published: January 2005

Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows:
equation image

Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10−6 exp { z−(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10−12 cm3/sec independent of temperature, k1a = 1.2 × 10−11 exp {−(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10−13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (−2b), which was found to have a rate coefficient k−2b = 6 × 1017 exp {−26,000/RT} sec−1 based on the value of k1a given above. The intermediate can also decompose via
equation image
Reaction (10b) is at least partially heterogeneous.
Computer study of the hydrogen atom recombination reaction under high pressure conditions
Authors: Stace A. J. , Murrell J. N.
Published: January 2005

The hydrogen‐atom recombination reaction has been simulated using a molecular dynamics technique recently formulated by the authors [1]. The rate of recombination has been calculated over a range of temperatures and inert gas concentrations (He and Ar) and agrees well with available experimental data. The calculations reproduce the negative activation energy characteristic of an atom recombination process. Over the range of conditions studied recombination was found to proceed via the energy transfer mechanism only, no evidence of bound HAr or HHe species was observed. Recombination was found to occur through an intermediate metastable diatomic molecule which is in equilibrium with its environment and from which there is a bottleneck to the formation of a stable molecule. The initial formation of a metastable species is sensitive to the hydrogen‐inert gas potential, but relaxation of the total energy is primary determined by the mass of the third‐body and the collision frequency.
The heat of formation of the acetonyl radical VLPP studies of acetonyl bromide, isopropenylmethylether, and hexanedione‐2,5 in a search for acetonyl stabilization energy
Authors: Zabel F. , Benson S. W. , Golden D. M.
Published: January 2005

The decomposition of acetonyl bromide, isopropenylmethylether, and hexanedione‐2,5 was studied using the very‐low‐pressure pyrolysis (VLPP) technique. The acetonyl radical is a product of each reaction. Arrhenius parameters determined are or acetonyl bromide ← acetonyl + Br:

and for isopropenylmethylether ← acetonyl + CH3:

These lead to values of acetonyl stabilization energy (SE) of 0.8 and −4.0 kcal/mol, respectively. Comparison of the pyrolyses of hexanedione‐2,5 and 2,5‐dimethylhexane indicate a value of SE ∼ 2 kcal/mol. The total of these results is taken, along with previous work, to indicate that 0 ≲ SE ≲ 2 kcal/mol.
Activation parameters and kinetic isotope effect in the system tropaeolin O‐OH−
Authors: Perlmutter‐Hayman Berta , Shinar Ruth
Published: January 2005

The kinetics of the deprotonation of tropaeolin O by OH− ions was investigated between 9° and 30°C, and by OD− ions at 24.7°C. The pH range was 10.7–12.5, and the ionic strength 0.1M throughout. All results were obtained by the temperature jump method. On the basis of a mechanism suggested earlier, rate constants k31 for the reaction between OL− and the internally bonded weak acid and k32 for the opening of the internal hydrogen bond were evaluated. The activation energies in ordinary water were found to be ΔH≠31 = 3.6 kcal/mol, ΔS≠31 = –19 eu, and ΔH≠32 = 27 kcal/mol, ΔS≠32 = 46 eu. The kinetic isotope effect was k31/k31 ∼ 1.5 and k32/k32 ∼ 0.9. The unusual results for reaction path
equation image
are discussed in terms of solvent participation.
Kinetics of the thermal decomposition of trans‐1,2‐dicyanocyclobutane
Authors: King Keith D. , Goddard Richard D.
Published: January 2005

The kinetics of the thermal decomposition of trans‐1,2‐dicyanocyclobutane, which yields only vinyl cyanide, have been studied in the temperature range of 570°‐660°K using a stirred‐flow reactor. The reaction was found to be first order and homogeneous with rate constants represented by the Arrhenius equation

where θ = 2.303 RT kcal/mol. The Arrhenius parameters are considerably higher than previously reported. On the assumption of a biradical mechanism the results are consistent with a cyano stabilization energy of ∼5 kcal/mol, in good agreement with the results of recent studies of related systems.
The thermal reaction of 2‐pentene around 500°C at low extent of reaction
Authors: Perrin D. , Richard C. , Martin R.
Published: January 2005

The thermal reaction of 2‐pentene (cis or trans) has been performed in a static system over the temperature range of 470°–535°C at low extent of reaction and for initial pressures of 20–100 torr. The main products of decomposition are methane and 1,3‐butadiene. Other minor primary products have been monitored: trans‐2‐pentene, trans‐ and cis‐2‐butenes, ethane, 1,3‐pentadienes, 3‐methyl‐1‐butene, propylene, 1‐butene, hydrogen, ethylene, and 1‐pentene. The initial orders of formation, 0.8–1.1 for most of the products and 1.5–1.8 for 1‐pentene, increase with temperature. The formation of the products and the influence of temperature on their orders can be essentially explained by a free radical chain mechanism. But cis–trans or trans–cis isomerization and hydrogen elimination from cis‐2‐pentene certainly involve both molecular and free radical processes. The formation of 1‐pentene mainly occurs from the abstraction of the hydrogen atom of 2‐pentene by resonance stabilized free radicals (C5H9.).
Very low‐pressure pyrolysis (VLPP) of but‐1‐yne the heat of formation and stabilization energy of the propargyl radical
Authors: King Keith D.
Published: January 2005

The unimolecular decomposition of but‐1‐yne has been investigated over the temperature range of 1052° – 1152°K using the technique of very low‐pressure pyrolysis (VLPP). The primary process is CC bond fission yielding methyl and propargyl radicals. Application of RRKM theory shows that the experimental rate constants are consistent with the highpressure Arrhenius parameters given by

where θ = 2.303 RT kcal/mol. The parameters are in good agreement with estimates based on shock‐tube studies. The activation energy, combined with thermochemical data, leads to DH°[HCCCH2CH3] = 76.0, ΔH(HCCĊCH2,g) = 81.4, and DH° [HCCCH2H] = 89.2, all in kcal/mol at 300°K. The stabilization energy of the propargyl radical SE° (HCCĊCH2) has been found to be 8.8 kcal/mol. Recent result for the shock‐tube pyrolysis of some alkynes have been analyzed and shown to yield values for the heat of formation and stabilization energy of the propargyl radical in excellent agreement with the present work. From a consideration of all results it is recommended that ΔH(HCCĊCH2,g) = 81.5±1.0, DH[HCCCH2H] = 89.3 ± 1.0, and SE° (HCCĊCH2) = 8.7±1.0 kcal/mol.
The mechanism of the photochemical reactions of SO2 with isobutane excited at 3130 Å
Authors: Su Fu , Calvert Jack G.
Published: January 2005

The mechanism of the reactions of electronically excited SO2 with isobutane has been studied through the measurement of the initial quantum yields of product formation in 3130 Å irradiated gaseous binary mixtures of SO2 and isobutane and ternary mixtures of SO2, isobutane, C6H6 or CO2. Under low‐pressure conditions (P < 10 torr) the kinetic treatment of the present data shows that only one singlet and one triplet state, presumably the 1B1 and 3B1 states, are involved in the photoreaction mechanism. The data give k2a = 8.4 × 109; SO2(1B1) + isobutane → products (2a); k5a ≃ k5 = 8.7 × 108 l./mol·sec; SO2(3B1) + isobutane → products (5a) SO2(3B1) + isobutane → (SO2) + isobutane (5b) k1a/k1 = 0.145 ± 0.037; SO2(1B1) + SO2 → SO2(3B1) + SO2 (1a) SO2(1B1) + SO2 → (2SO2) (1b) k2b/k2 = 0.273 ± 0.018; SO2(1B1) + isobutane → SO2(3B1) + isobutane (2b); SO2(1B1) + isobutane → (SO2) + isobutane (2c) error limits are ± 2 σ. The contribution from the excited SO2(1B1) molecules to the quantum yields of the photolyses of SO2–isobutane mixtures is not negligible. Under high‐pressure conditions (P > 10 torr) the low‐pressure mechanism coupled with the saturation effect on the phosphorescence lifetimes of SO2(3B1) molecules cannot alone rationalize the quantum yields. The evaluation suggests that some nonradiative intermediate state (X) is involved in the formation of “extra” triplet molecules. This ill‐defined state decays largely nonradiatively to SO2 in experiments at low pressures, X → SO2 (12). In the presence of C6H6 the low‐pressure data give k7 = (8.5 ± 1.8) × 1010, and the high‐pressure data give k7 = (8.3 ± 0.6) × 1010 and (9.9 ± 0.9) × 1010l./mol·sec; SO2(3B1) + C6H6 → nonradiative products (7). These estimates are in good agreement with values directly measured from low‐pressure lifetime studies, (8.1 ± 0.7) × 1010 and (8.8 ± 0.8) × 1010l./mol·sec.
Thallation of fluorenes: A kinetic and mechanistic study
Authors: Narasimhan S. , Ramani P. V. , Venkatasubramanian N.
Published: January 2005

The kinetics of thallation of fluorene with thallium triacetate (TTA) in HOAc‐H2SO4 solutions led to the rate expression

The rate of thallation is found to increase with increasing acid concentration, and a sixth‐order dependence on [H2SO4] is observed. Decrease in solvent polarity increases the rate of thallation. The effect of substituents is in accord with the electrophilic substitution at an aromatic system. Thallation occurs at 4‐position. A mechanism similar to aromatic bromination is proposed for the thallation of fluorene.
The recombination of iodine atoms in the presence of nitric oxide
Authors: Basco N. , Hunt J. E.
Published: January 2005

The recombination of iodine atoms following the flash photolysis of iodine in the presence of nitric oxide is interpreted through the mechanism
equation image
with k1 = 3.5 × 109 l.2/mol2·sec; k2 ≈ 1 × 1011 l./mol·sec; k3 = 2.1 × 107 l./mol·sec at 298°K; E3 = 11 kJ/ mol; and ΔH°1 = 76 ± 6 kJ/mol. Lower and upper limits for the equilibrium constant are also established. The absorption spectrum of INO has been extended down to 223 nm and extinction coefficients for the region of 223–310 nm and 360–460 nm have been measured.
Chemical lasers produced from O(3P) atom reactions. V. CO laser emissions and vibrational population distribution in the flash‐initiated SO2‐CFBr3 system
Authors: Hsu David S. Y. , Lin M. C.
Published: January 2005

CO laser emission at 5 μm was detected when SO2 and CFBr3 were flash photolyzed in the vacuum ultraviolet above 165 nm. Over 40 vibrational–rotational transitions ranging from Δv = 2 → 1 to 14 → 13, with the exception of those between 8 → 7 and 11 → 10, were identified. The CO emission is believed to result from the O + CF reaction:
equation image

The vibrational population of the CO has been measured by means of a CO laser resonance absorption method. The CO was found to be vibrationally excited to v = 24 with a vibrational temperature of about 1.4 × 104°K. The “surprisal analysis” of the observed CO distribution showed the possible occurrence of a minor process (presumably O + CFBr) that generated vibrationally colder CO. The effects of various additives on the CO emission were also examined. The addition of CO2 to a D2‐SO2‐CFBr3‐He mixture resulted in a simultaneous osciallation at 3.6, 5, and 10.6 μm due to DF, CO, and CO2, respectively. Additionally, the utilization of the O + CFn (n = 1, 2, 3) reactions as F‐atom sources for HF‐laser operation in flash‐initiated systems were demonstrated.
The mechanism of methanol formation and other reactions following formaldehyde adsorption on Ni(110)
Authors: Dickinson J. Thomas , Madix Robert J.
Published: January 2005

The adsorption/desorption and reactive behavior of formaldehyde was studied on clean single‐crystal Ni(110) at adsorption temperatures down to 200 °K. For low exposures of the surface to formaldehyde, hydrogen and CO binding states were populated due to decomposition of the molecule upon adsorption. Higher exposures gave rise to a decomposition‐limited hydrogen peak exhibiting an activation energy of 20 kcal/gmol and an apparent frequency factor of 1014 sec−1. At initial coverages of H2CO exceeding about 0.5, monolayer methanol was observed to form. The formation of methanol involved a hydrogen atom transfer between two adsorbed H2CO molecules and did not occur totally via surface hydrogen. Self‐oxidation to form CO2 was also observed. The surface exhibited reaction heterogeneity, and the surface reactivity was observed to depend on the temperature of adsorption of reactants, suggesting strong adsorbate‐induced surface “reconstruction.”
Permanganate ion oxidations X. Kinetics and mechanisms of the initial stage in the oxidation of 4‐hydroxy‐2‐pyrimidinethiols
Authors: Freeman Fillmore , Bond Dorrece Lynn , Chernow Steven Martin , Davidson Pamela Ann , Karchefski Elaine Marie
Published: January 2005

Permanganate ion rapidly oxidizes the thiol group in 2‐thiouracils (2,3‐dihydro‐2‐thioxo‐4(1H)‐pyrimidinones, 4‐hydroxy‐2‐pyrimidinethiols) to the corresponding uracil‐2‐sulfonates in phosphate‐buffered solutions. The oxidations, which are first order in oxidant and first order in reductants, are characterized by relatively small energies of activation (Ea ≅ 4.3–6.7kcal/mol) and relatively large negative entropies of activation (ΔS‡ = −24.9–−34.4 eu). The relative rates of oxidation of 2‐thiouracil (2), 6‐methyl‐ (4), 6‐n‐propyl‐ (6), 1,6‐dimethyl‐(8), and 3,6‐dimethyl‐2‐thiouracil (9) are 1.00:1.23:0.98:7.32:2.54. The rate of oxidation of 1,3,6‐trimethyl‐2‐thiouracil (12) is several orders of magnitude slower than that of the other thiouracils. Although the thiol group or thiolate anion is probably involved in the rate‐determining step, several other possible mechanisms are also considered.
The participation of aromatic neighboring groups in gas‐phase elimination reactions
Authors: Hernandez A. Jose A. , Chuchani Gabriel
Published: January 2005

The gas‐phase pyrolysis of 2‐chloroethylbenzene and p‐methoxy‐2‐chloroethylbenzene was studied in a static system over the temperature range of 411°–471°C and a pressure range of 39–202 mm Hg. The reactions in seasoned vessels, with the propene inhibitor always present, were homogeneous, first‐order, and unimolecular. The rate constants are given by the Arrhenius equation for 2‐chloroethylbenzene:

and for p‐methoxy‐2‐chloroethylbenzene:

The presence of phenyl substituents in the β position of ethyl chloride has been found to provide anchimeric assistance in these elimination reactions.
The gas‐phase pyrolysis of alkyl nitrites VI. t‐Amyl nitrite
Authors: Batt L. , Islam T. S. A. , Rattray G. N.
Published: January 2005

The rate of decomposition of tert‐amyl nitrite (t‐AmONO) has been studied in the absence (120°–155°C) and presence (160°–190°C) of nitric oxide. In the absence of nitric oxide for low concentrations of tert‐amyl nitrite (∼10−4M) and small extents of reaction (∼1%), the first‐order homogeneous rates of acetone formation are a direct measure of reaction (1) since k3a ≫ k2(NO):
equation image
The rate of acetone formation is unaffected by the addition of large amounts of carbon tetrafluoride or isobutane (∼1 atm) but is completely suppressed by large amounts of nitric oxide (1 atm 120°–155°C).

The rate of reaction (1) is given by k1 = 1016.3±0.1 10−40.3±0.1/θ sec−1. Since (E1 + RT) and ΔH°1 are identical, both may be equated with D(t‐AmO – NO) = 40.9 ± 0.1 kcal/mol and E2 = 0 ± 0.1 kcal/mol. The thermochemistry leads to the result that ΔH°f (t‐AmO) = −26.6 ± 1 kcal/mol. From ΔS°1 and A1, k2 is calculated to be 1010.5±0.2 M−1·sec−1.

Although the addition of nitric oxide completely suppresses acetone formation at lower temperatures, it reappears at higher temperatures. This is a result of reaction (3a) now competing with reaction (2), thus allowing k3a to be determined. The rate constant for reaction (3a) is given by k3a = 1014.7 ± 0.2 10−14.3 ± 1/θ sec−1. There are two possible routes for the decomposition of the tert‐amyloxyl radical:
equation image
The dominating process is (3a). From the result at 160°C that k3a/k3b = 80, we arrive at the result k3b = 1015.0–18.7/θ sec−1.

In addition to the products accounted for by the radical split (1), methyl‐2‐but‐1‐ene and methyl‐2‐but‐2‐ene are produced as a result of the six‐centre elimination of nitrous acid (5):
equation image

The ratio k5a/k5b was 0.35. Unlike tert‐butyl where the rates of the two paths were comparable [(l) and (5)], here the total rate of the elimination process was only 0.5% that of the radical split (1). The reason for this is not clear.
Stopped‐flow studies of the mechanisms of ozone–alkene reactions in the gas phase propene and isobutene
Authors: Herron John T. , Huie Robert E.
Published: January 2005

The reactions of ozone with propene and isobutene have been studied in the gas phase at 298°K and 530 Pa (4 torr) using a stopped‐flow reactor coupled to a photoionization mass spectrometer. Reactant and product concentrations were followed as a function of reaction time. The major reaction products monitored were CH2O, CH3CHO, CO2, and H2O from the propene reaction, and CH2O, (CH3)2CO, CO2, and H2O from the isobutene reaction. The observations were interpreted on the basis of the Criegee mechanism for ozonolysis in solution: magnified image for which we find kA≈kB.In the gas phase the carbene peroxy radical is postulated to isomerize and decompose into molecular and free‐radical products.
The reaction of hydrogen atoms with 1‐butanethiol and thiolane the role of chemically activated 1‐butanethiol
Authors: Horie Osamu , Nishino Junya , Amano Akira
Published: January 2005

The reaction of 1‐butanethiol with hydrogen atoms has been studied at temperatures of 295° and 576° K under the pressure of 660 Pa, using a conventional discharge‐flow apparatus. The reaction products (besides hydrogen sulfide and methane) under the low conversion range (∼10%) consisted mainly ofn‐butane, 1‐butene, and propylene‐propane, with the relative yields of 70, 25, and 5% at 295° K and 25, 50, and 10% at 576°K. Analysis of kinetic equations by numerical integration indicates that the following initial steps are consistent with the experimental results:equation imagewhere the following expressions have been derived fork1andk2:The subsequent reaction of the butylthio radical with hydrogen atoms leads to the chemically activated 1‐butanethiol which either stabilizes to 1‐butanethiol or decomposes to 1‐butene and hydrogen sulfide, depending on the experimental conditions. A similar analysis of the data on the thiolane‐H system has yielded the following rate parameters for the initial step to form the 4‐mercapto‐1‐butyl radical:equation image.
Kinetics of the reaction O(3P) + SO2 + M → SO3 + M over the temperature range of 299°–440°K
Authors: Atkinson R. , Pitts J. N.
Published: January 2005

Rate constants for the reaction O(3P) + SO2 + M have been determined over the temperature range of 299°–440°K, using a flash photolysis–NO2 chemiluminescence technique. For MAr, the Arrhenius expression

was obtained. At room temperature k2Ar = (1.05 ± 0.21) × 10−33 cm6/molec2·sec. In addition, the rate constants k2 = (1.37 + 0.27) × 10−33 cm6/molec2·sec, k2 = (9.5 ± 3.0) ± 10−33 cm6/molec2·sec, k3 = (1.1 ± 0.2) ± 10−31 cm6/molec2·sec, and k3 = (2.6 − 0.9) ± 10−31 cm6/molec2·sec were obtained at room temperature where k3M is the rate constant for the reaction O + NO + M → NO2 + M. The rate data are compared and discussed with literature values.
Studies by the electron cyclotron resonance (ECR) technique. XII. Interactions of thermal‐energy electrons with the molecules CHF3, CHClF2, and CHCl2F
Authors: Christodoulides A. A. , Schumacher R. , Schindler R. N.
Published: January 2005

Using the ECR technique the electron scavenging properties of the halomethanes CHF3, CHClF2, and CHCl2F were investigated. A brief discussion is given on the evaluation of experimental data for inefficient polar scavengers. Absolute attachment rate constants were obtained from the decrease of the cyclotron resonance signal upon addition of the above scavengers. For the molecules CHF3 and CHCl2F the activation energies for the capture processes are given. Possible capture mechanisms are discussed.
Quenching of biacetyl (3Au) molecules by near‐resonant and off‐resonant collisional partners
Authors: Wampler F. B. , Oldenborg R. C.
Published: January 2005

Laser‐induced time‐resolved phosphorescence has been used to evaluate the quenching of gaseous biacetyl (3Au) molecules by various molecules at 25°C. The quenching of biacetyl (3Au) molecules by biacetyl itself was not detectable under our experimental conditions, and a pressure‐independent lifetime of 1.70 ± 0.08 msec was found. The bimolecular rate constants (units of l/mol·sec) for quenching of the 3Au molecules by cis‐2‐pentene, trans‐2‐pentene, cis‐1,3‐pentadiene, trans‐1,3‐pentadiene, and oxygen were found to be (3.3 ± 1.9) × 103, (4.0 ± 0.2) × 104, (3.9 ± 0.1) × 108, (1.3 ± 0.1) × 108, and (5.2 ± 0.4) × 108, respectively.
The kinetics of ClO formation in the flash photolysis of chlorine–oxygen mixtures
Authors: Ashford R. D. , Basco N. , Hunt J. E.
Published: January 2005

The production of ClOO and ClO radicals following the flash photolysis of chlorine + oxygen mixtures has been studied. For the mechanism
equation image
the following kinetic parameters were measured: k3K = 1.3 × 1010 l2/mol2·sec; k2/k3 = 17; and k3/ϵ(ClOO; 250 nm) = 9.7 × 105 cm/sec. Then k3 = 5.9 × 109 l/mol·sec, k2 = 1.0 × 1011 l/mol·sec, and ϵ(ClOO; 250 nm) = 6.1 × 103 l/mol·cm. From limits established for the equilibrium constant K, ΔH°f (ClOO) = 94 ± 2 kJ/mol.
Thermal decomposition of ethane
Authors: Olson D. B. , Tanzawa T. , Gardiner W. C.
Published: January 2005

The decomposition of C2H6in Ar was studied by laser‐absorption and laser‐schlieren measurements of the reaction rate behind incident shock waves with 1300 <T< 2500°K and 1.1 < ρ < 4.4 × 10−6mol/cm3. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14‐reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expressionk(cm3/mol˙sec) = 2 × 10111T−25.26exp(−80 320/T) was found for the primary dissociation step C2H6+ M  CH3+ CH3+ M under the conditions studied; no difference in rate was discernable between M  Ar and M  C2H6. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low‐pressure limiting rate constants and found to be concordant.
Competitive chlorination–dehydrochlorination of 1,1,1,2‐C2H2Cl4
Authors: Olbregts J.
Published: January 2005

The competitive photochlorination and chlorine photosensitized dehydrochlorination of 1,1,1,2‐C2H2Cl4 have been studied over the temperature range of 349.4–404.5 K after less than 1% conversion. The results are discussed and a value of

is proposed for the reaction

This result, combined with existing thermochemical data, indicates that there is no evidence of an activation energy for the addition of a Cl atom on the most chlorinated carbon in trichloroethylene: in that case the selectivity of the addition of Cl on the less chlorinated carbon should not depend on temperature.
Kinetics and mechanism for the iodination of methylmalonic acid
Authors: Furrow Stanley D.
Published: January 2005

The reaction\documentclass{article}\pagestyle{empty}\begin{document}$ CH\left({CH_3 } \right)\left({COOH} \right)_2 + I_2 \rightleftharpoons CI(CH_3)\left({COOH} \right)_2 + H^ + + I^ - $\end{document} was followed spectrophotometrically at 353 nm and 470 nm at 25°C under various conditions of pH and methylmalonic acid concentration. The equilibrium constant for the reaction is 0.11 ± 0.02. An iterative technique was used to integrate postulated rate equations. Agreement between experimental and calculated absorbance versus time curves was generally better than 0.005 A (approximately 5% of maximum) at both wavelengths for a mechanism where the rate‐determining step is formation of an enolate (k = 1.63 Θ 10−4 ± 0.03 Θ 10−4 sec−1). The enolate may be rapidly transformed to the enol or enol carboxylate anion depending on the pH. All three forms are rapidly iodinated. The mechanism of general base catalysis is supported by rate increases proportional to base concentration in buffer solutions. The bases, acetate ion, chloracetate ion, sulfate ion, dichloracetate ion, and water, follow a Brønsted relationship with β = 0.7.
The very‐low‐pressure study of the kinetics and equilibrium: Cl + CH4 ⇄ CH3 + HCl at 298 K. The heat of formation of the CH3 radical
Authors: Baghal‐Vayjooee Mohammad H. , Colussi Agustin J. , Benson Sidney W.
Published: January 2005

The bimolecular rate constant for the direct reaction of chlorine atoms with methane was measured at 25°C by using the very‐low‐pressure‐pyrolysis technique. The rate constant was found to be

In addition, the ratio k1/k−1 was observed with about 25% accuracy: K1(298) = 1.3 ± 0.3. This gives a heat of formation of the methyl radical ΔH° f 298(CH3) = 35.1 ± 0.15 kcal/mol. A bond dissociation energy BDE (CH3  H) = 105.1 ± 0.15 kcal/mol in good agreement with literature values was obtained.
Collisional deactivation of O2(1Σg+)
Authors: Chatha J. P. S. , Arora P. K. , Raja Smt. Nalini , Kulkarni P. B. , Vohra K. G.
Published: January 2005

Relaxation rates for O2(1Σg+) by nonradiative pathways have been determined using the fast‐flow technique. O2(1Σg+) is formed from O2(1Δg) by an energy pooling process. O2(1Δg) is generated by passing purified oxygen through a microwave discharge. Oxygen atoms are removed by distilling mercury vapor through the discharge zone. It has been observed that the wall loss rate for O2(1Σg+) decreases with increasing pressure of oxygen and thus appears to be diffusion controlled. Quenching rate constants for O2, N2, and He have been determined and found to be (1.5 ± 0.1) × 104, (1.0 ± 0.05) × 106 and (1.2 ± 0.1) × 105 l./mol·sec, respectively.
The photolysis of n‐butyraldehyde in isooctane at 313 nm
Authors: Förgeteg S. , Bérces T.
Published: January 2005

The effects of aldehyde concentration, incident light intensity, and temperature on the quantum yields of reaction products were studied. Mechanisms for primary and secondary photochemical processes were suggested, and primary quantum yields as well as rate constant ratios were derived. Reversibility of intramolecular γ‐hydrogen transfer and disproportionation of the radical pair formed in the reaction of an excited triplet and ground state molecule were shown to provide important pathways for radiationless decay of the triplet state.
Comments on the paper “reaction between nitrous acid and hydrogen peroxide in perchloric acid medium”
Authors: Haim Albert , Wang Nun‐Yii , Bonner Francis T.
Published: January 2005

No Absract.
Automatic sensitivity analysis of kinetic mechanisms
Authors: Koda Masato , Mcrae Gregory J. , Seinfeld John H.
Published: January 2005

An algorithm for the automatic sensitivity analysis of kinetic mechanisms based on the Fourier amplitude sensitivity test (FAST) method of Shuler and co‐workers is reported. The algorithm computes a measure of the relative sensitivity of each concentration to each parameter of interest, such as rate constants, Arrhenius parameters, stoichiometric coefficients, and initial concentrations. Arbitrary variations in the magnitude of the parameters are allowable. The algorithm is illustrated for the simple example of computing the sensitivity of the concentration of species A to variation of the two Arrhenius parameters for the hypothetical reaction A + A →.
Chlorine atom and ClO wall reaction products
Authors: Martin L. Robbin , Wren Anthony G. , Wun Marilyn
Published: January 2005

The products of the heterogeneous reactions of chlorine atoms and chlorine oxide radicals with acid coated Pyrex walls have been directly determined for the first time. Contrary to the usual assumption that chlorine atoms recombine to form Cl2, we find that the major product is HCl, with small amounts of perchlorate also formed. Similarly, ClO radicals form HCl rather than Cl2. The source of hydrogen for these reactions is probably the water always found in this type of vacuum system. These results may change the interpretation of flow tube experiments with chlorine atoms. Application to the H + HCl reaction is discussed as an example.
Absolute quantum yield of O(1D2) in the photolysis of ozone in the hartley band
Authors: Kajimoto O. , Cvetanovi R. J.
Published: January 2005

The absolute quantum yield of O(1D2) in the photolysis of ozone in the Hartley band, between about 230 and 280 nm, has been determined using the isotopic exchange reaction between C16O2 and 18O(1D2). A value of 1.00 ± 0.05 has been obtained within a 95% confidence limit. A value of unity may therefore be accepted as the average quantum yield of O(1D2) atoms in the 230–280‐nm region within an uncertainty of only several percent.
Homogeneous decomposition of vinyl ethers. The heat of formation of ethanal‐2‐yl
Authors: Rossi M. , Golden D. M.
Published: January 2005

The thermal unimolecular decomposition of three vinylethers has been studied in a VLPP apparatus. The high‐pressure rate constant for the retro‐ene reaction of ethylvinylether was fit by log k (sec−1) = (11.47 + 0.25) ‐ (43.4 ± 1.0)/2.303 RT at  = 900 K and that of t ‐ butylvinylether by log k (sec−1) = (12.00 ± 0.27) ‐ (38.4 ± 1.0)/2.303 RT at  = 800 K. No evidence for the competition of the higher energy homolytic bond‐fission process could be obtained from the experimental data. The rate constant compatible with the CO bond scission reaction in the case of benzylvinylether was log k (sec−1) = (16.63 ± 0.30) ‐ (53.74 ± 1.0)/2.303 RT at  = 750 K. Together with ΔHf,3000(benzyl·) = 47.0 kcal/mol, the activation energy for this reaction results in ΔHf,3000(CH2CHO) = +3.0 ± 2.0 kcal/mol and a corresponding resonance stabilization energy of 3.2 ± 2.0 kcal/mol for 2‐ethanalyl radical.
Redox kinetics of metal complexes in nonaqueous solutions. V. Kinetics and mechanism of the iron (II) reduction of the acetylacetonates of manganese (III) and cobalt (III) in acetonitrile
Authors: Schmid Roland , Sapunov Valentin N.
Published: January 2005

The electron transfer step of the reduction of Mn(acac)3 and Co(acac)3 by Fe(II) in acetonitrile is preceded by the one‐ended dissociation of an acac ligand and the formation of a binuclear bridged complex. After the electron transfer has taken place through the bridging ligand, the complex dissociates into the products M(acac)2 (M = Mn, Co) and Fe(acac)2+. These primary reaction products could not be identified, since the transfer of acac from M(acac)2 to Fe(acac)2+ is too rapid, producing ultimately Fe(acac)3 and M2+. The M(III)‐oxygen cleavage is accelerated by M(acac)2. Furthermore, the dissociation of the binuclear intermediate is catalyzed by the M(acac)3 reactant. Mn(acac)3 is reduced more than a thousand times faster than Co(acac)3.
Rate of decomposition of hexafluoroazomethane and the absolute rate of recombination of trifluoromethyl radical at higher temperatures
Authors: Rossi M. , Golden D. M.
Published: January 2005

The unimolecular homogeneous decomposition of hexafluoroazomethane was studied in a VLPP apparatus in the temperature range 720–1050 K and is consistent with the following Arrhenius parameters:

at 900 K, where the A factor was assumed to be the same as for 2,2′‐azoisobutane. The homogeneous rate of recombination of ·CF3 radicals at temperatures around 1000 K was also studied under VLPP conditions and was found to be in the fall‐off region, corresponding to k/k∞ = 8.5 × 10−3 when a rotational transition‐state model was used. This model predicts an essentially constant value of kr∞ of 109.7 over the temperature range 300–1000 K.
Thermal decomposition of hexamethylethane in a flow system
Authors: Walker James A. , Tsang Wing
Published: January 2005

Hexamethylethane has been decomposed in a flow system in the temperature range of 700–900 K. The mechanism involves carbon–carbon bond cleavage at the most highly substituted position and rapid formation of isobutene from the t‐butyl radical. The rate expression is

and is completely consistent with deductions from radical buffer, shock‐tube, and direct recombination studies. Of special importance is experimental evidence for large decreases of the A factor with increasing temperature and a high heat of formation for the t‐butyl radical, ΔHf(tC4H9·)300 = 52.7 ± 6 kJ.
Sampling effects on observed cyclopropane isomerization in a single pulse shock tube
Authors: Jeffers Peter M. , Northing Jeffrey
Published: January 2005

Cyclopropane in argon mixtures was heated in a single‐pulse shock tube, and syringes were used to withdraw samples from both the central gas slug and the gas adjacent to the tube walls. Differences were observed in the measured conversion, with larger conversion found in the center location. The discrepancy increased with increasing conversion, and the results indicate that boundary‐layer effects can seriously affect the results of absolute single‐pulse shock‐tube studies when percent conversion is large.
The absolute rate constant for the metathesis t‐C4H9• + DI → C4H9D + I• and the heat of formation of the t‐butyl radical
Authors: Rossi Michel , Golden David M.
Published: January 2005

The Arrhenius parameters for the title reaction have been measured in a very‐low‐pressure pyrolysis apparatus in the temperature range 644–722 K and are given by log k2 (M−1 · sec−1) = 9.68 ‐ 2.12/θ, where θ = 2.303RT in kcal/mol. Together with the published Arrhenius parameters for the reverse reaction from iodination studies, they result in a standard heat of formation of the t‐butyl radical of 8.4 kcal/mol, accepting S0(C4H9·) = 72.2 e.u. at 300 K from other kinetic data, and thus confirm the accepted value for ΔHf0(t‐C4H9·), at variance with recent investigations which yielded significantly higher values. This value for ΔHf0(t‐C4H9·) results in a bond‐dissociation energy (BDE) for isobutane of 92.7 kcal/mol.
Reaction of methoxy radicals with oxygen. I. Using dimethyl peroxide as a thermal source of methoxy radicals
Authors: Batt L. , Robinson G. N.
Published: January 2005

Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110–160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction:
equation image
a value was determined of the rate constant for the reaction of methoxy radicals with oxygen:
equation image
is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k4 is given by the expression

In terms of atmospheric chemistry, this corresponds to a value of 105.6 M−1·sec−1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 107.7 M−1·sec−1 for k4. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3):
equation image
In particular k3 is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex.
Reduction of hexachloroiridate (IV) by benzene‐1,2‐diol in aqueous perchloric acid
Authors: Morris D. F. C. , Ritter T. J.
Published: January 2005

The kinetics of the reaction between benzene‐1,2‐diol(catechol) and hexachloroiridate (IV) have been measured in aqueous acidic perchlorate solutions by the stopped‐flow method. The reaction is second order overall, and first order in each reactant. A reverse reaction also occurs, but it is much slower than the forward process. Observed rate constants are dependent on acidity, but the variation can be attributed to activity rather than mechanistic effects. The reaction appears to proceed predominantly by an outer sphere electron transfer mechanism, yielding o‐benzoquinone and hexachloroiridate (III), although monoaquopentachloroiridate (III) is formed also at the higher [catechol]/[IrCl62−]ratios.
A Program package using stiff, sparse integration methods for the automatic solution of mass action kinetics equations
Authors: Carver M. B. , Boyd A. W.
Published: January 2005

A portable program package, MACKSIM, for mass action chemical kinetics simulation, is discussed. As these kinetics are readily expressed in explicit mathematical terms, such a package contains two major and distinct modules, the numerical analysis and the user interface. For the first, MACKSIM uses the latest proven developments incorporating sparse matrix techniques in the backward difference predictor corrector methods originated by Gear for the integration of stiff ordinary differential equations, and thus requires minimal computing time to solve large systems of equations. For the second, the program provides a flexible interface which permits simple specification and variation of reactions, requires no special character input, and has no limit on the number of reactions or species involved other than that imposed by the size of the computer. The technology of these components is discussed briefly, the use of the package for standard reactions is illustrated, and current applications are mentioned.
The kinetics of the interaction of peroxy radicals. I. The Tertiary Peroxy Radicals
Authors: Nangia Prakash S. , Benson Sidney W.
Published: January 2005

Existing data on the self‐reactions of tertiary peroxy radicals RO2 has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths. For R = t‐Butyl, these are logkt(M−1sec−1) = 7.1 ‐ (7.0/θ) and logknt(M−1sec−1) = 9.4 ‐ (9.0/θ), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1‐diphenylethyl have been discussed in terms of a much greater cage recombination of cumyloxy radicals as contrasted with t‐butoxy radicals. It is shown that for benzyl peroxy radicals, the R—O bond dissociation energy is sufficiently low (18–20 kcal) that reversible dissociation into R˙ + O2 opens a competing second‐order path to fast recombination R˙ + RO → ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,1‐diphenyl ethyl peroxy radicals at (O2) < 10−3M. At very low RO concentrations (<10−5M), in the absence of added O2, an apparent first‐order disappearance of RO can occur reflecting the rate determining breaking of the cumyl—O bond followed by the second step above. The thermochemistry of RO is used to show that the reaction of R2O4 → 2RO + O2 must be concerted and cannot proceed via RO which is too unstable and cannot form even from RO˙ + O2.