bluuebunny/crossref_metadata_2025 huggingface dataset:
The reaction of O(1D) with CH4
Authors: Greenberg Raymond I. , Heicklen Julian
Published: January 2005

The room‐temperature photolysis of N2O (10–100 torr) at 2139 Å to produce O(1D) has been studied in the presence of CH4 (10–891 torr). The reactions of O(1D) with CH4 were found to be

The method of chemical difference was used to measure the rate constant ratio k4/(k2 + k3), where reactions (2) and (3) are

The CH3 radicals produced in reaction (4) react with the O2 and NO produced in reactions (2) and (3). Thus, near the endpoint of the internal titration, ϕ{C2H6} gives an accurate measure of k4/(k2 + k3). For the translationally energetic O(1D) atoms produced in the photolysis, k4/(k2 + k3) = 2.28 ± 0.20. However, if He is added to remove the excess translational energy, then k4/(k2 + k3) drops to 1.35 ± 0.3.
Kinetics of the “a” and “b” band emissions of mercury excimers with added gases
Authors: Penzes S. , Sandhu H. S. , Strausz O. P.
Published: January 2005

The kinetics of the “a” and “b” band emissions arising from the 1Σ ← 3Ou and 1Σ ← 3lu transitions of the diatomic mercury molecule at λmax ∼ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N2, C2H6, C3H8, and N2O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg2(3lu) + N2 → Hg2(3Ou) + N2 and Hg2(3Ou) + RH → Hg2(1Σ) + RH, where RH = C2H6 or C3H8. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(3P0) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry.
Pyrolysis of 4,4‐bisperfluoromethylbutene‐1,4 01 in the gas phase
Authors: Gordon Alvin S.
Published: January 2005

Pyrolysis of (CF3)2C(OH)CH2CH=CH2, the reverse of the reaction between perfluoroacetone and propene, has been studied in the gas phase between 475° and 598°K. Even at 573°K, the unimolecular reaction rate constant appears to be in its pressure‐independent region at 20.0 torr pressure. In a quartz vessel, the decomposition is homogeneous. The specific unimolecular rate constant is

where the limits are for one standard deviation. Combining these results with the previously reported results on the reverse reaction, the equilibrium constant for the reaction

is

It is noteworthy that in the temperature range of the study of the forward reaction (448° to 573°K), the percentage of back reaction in the times of the experiments varies from less than 0.1 to 1.5. Using group additivities and the above ΔH0, ΔH of (CF3)2CO is calculated to be −325.2 kcal/mole at 600°K and the average CC bond is 42.0 kcal/mole.
A Kinetic study of the reaction of nitrogen dioxide with tetrafluoroethylene
Authors: Spicer Chester W. , Heicklen Julian
Published: January 2005

The reaction of NO2 with C2F4 was studied at 30°, 68°, 114°, and 157°C by in situ monitoring the infrared absorption bands of the products. The major primary products of the reaction are O2NCF2CFO and FNO. Smaller amounts of CF2O (and presumably NO) are also produced. There was no evidence for other primary products, though they may have been produced in minor amounts. The rate laws for the production of both O2NCF2CFO and CF2O are first order in both [NO2] and [C2F4]. CF2O production is at least partly heterogeneous as demonstrated by packing the quartz reaction vessel with Pyrex beads and by using a Monel cell. The homogeneous rate constant obtained from the high‐temperature results gives a rate constant of 3.4 × 108 exp (minus;17000/RT) M−1sec−1 for CF2O production. Actually these Arrhenius parameters represent lower limits, since the heterogeneous reaction may still be playing a significant role. The production rate of O2NCF2CFO is not much affected by changing the nature of the surface or the surface to volume ratio. However the reaction may be heterogeneous, since the rate constant for its formation of 1.3 × 104 e×p (−7500/RT) M−1sec−1 has an abnormally low pree×ponential factor. E×periments in the presence of NO indicate that the mechanism for O2NCF2CFO formatlon is

The intermediate can also react with NO:

with k13/k12 = 1.3.
Absolute rate constants for reactions of free radicals in the high‐temperature photolysis of formamide vapor. Part I. Carbamyl radicals
Authors: Yokota T. , Back R. A.
Published: January 2005

The photolysis of formamide vapor at 2062 Å has been studied in a flow system with results essentially similar to those obtained previously under static conditions and higher conversions. The rotating‐sector technique has been applied to the radical‐chain decomposition of formamide under conditions (305°C, 11.5 torr) such that decomposition of the carbamyl (NH2CO) radical was rate controlling, so that [NH2CO] ≫ [NH2]. A rate constant of (3.1 ± 1.0) × 1010(M·sec)−1 was obtained for bimolecular chain termination by carbamyl radicals. A concurrent first‐order radical loss, probably at the surface, was taken into account by the treatment described by Shepp. Both oxamide and HNCO were tentatively identified as termination products, suggesting the occurrence of both combination and disproportionation,

but quantitative estimates of the relative rates were not possible. From the rate constant for chain termination, and relative rate constants obtained previously, Arrhenius parameters A∞ = (5.9 ± 2.0) × 1012 sec−1 and A0 = (1.04 ± 0.35) × 1014 (M·sec)−1 were estimated for the unimolecular decomposition of carbamyl radicals in the high and low pressure limits.
The reaction of O(1D) with H2O and the reaction of OH with C3H6
Authors: Simonaitis R. , Heicklen Julian
Published: January 2005

N2O was photolyzed at 2139 Å to produce O(1D) atoms in the presence of H2O and CO. The O(1D) atoms react with H2O to produce HO radicals, as measured by CO2 production from the reaction of OH with CO. The relative importance of the various possible O(1D )–H2O reactions is
equation image
The relative rate constant for O(1D) removal by H2O compared to that by N2O is 2.1, in good agreement with that found earlier in our laboratory. In the presence Of C3H6, the OH can be removed by reaction with either CO or C3H6:
equation image
From the CO2 yield, k3/k2 = 75,0 at 100°C and 55.0 at 200°C to within ± 10%. When these values are combined with the value of k2 = 7.0 × 10−13exp (–1100/RT) cm3/sec, k3 = 1.36 × 10−11 exp (–100/RT) cm3/sec. At 25°C, k3 extrapolates to 1.1 × 10−11 cm3/sec.
Heats of formation and kinetics of decomposition of nitroalkanes
Authors: Shaw Robert
Published: January 2005

Heats of formation of solid, liquid, and gaseous nitroalkanes have been shown mostly to obey group additivity. Group values have been obtained for carbon atoms attached to one, two, and three nitro groups. The heat of formation of 1,1,1,3,5,5,5,‐heptanitropentane, either solid or liquid, cannot be fitted to the scheme, even allowing for gauche effects. The differences between observed and estimated values for 1,1,1‐fluorodinitroalkanes and 1,2‐dinitroethane are larger than expected and should be further investigated. Activation energies have been calculated for decomposition by five‐center elimination of HONO from mononitro‐ and dinitroalkanes using thermochemistry and estimated activation energies for the reverse reactions. The key data for these estimates were previously reported activation energies for the decomposition of nitroethane and 1,2‐dinitropropane. The calculations also gave values for the heats of formation (in kcal/mole) of nitroethylene 12.4, and 1‐nitropropylene 5.6, and 2‐nitropropylene 1.6. Activation energies were calculated for the competing unimolecular reaction, CN bond fission, from thermochemistry and previously reported activation energies for the decomposition of 1,1‐ and 2,2‐dinitropropane. Comparison of Arrhenius parameters for the two competing processes, namely, HONO and CN bond fission, shows that, for the geminate dinitroethanes and dinitropropanes, CN bond fission is faster about 370°K and, for the mononitroalkanes and for all the mononitroalkanes and dinitroalkanes, CN bond fission is faster above 770°K.
The photochlorination of perfluorocyclopentene
Authors: Alberto Z. R. , Cosa J. J. , Staricco E. H.
Published: January 2005

The gas‐phase photochlorination of perfluorocyclopentene under continuous and intermittent illumination with 4360‐Å radiation was studied between 10° and 60°C. The rate constants for the reactions. (3)

(4)

were measured as k3 = (1.20 + 0.58) × 108 exp (−6.430 ± 177/RT) l·(mole sec) and k4 = (1.86 ± 0.76) × 107 l·(mole sec).
Kinetics of the thermal gas‐phase isomerization of 1,2‐epoxycyclohexane
Authors: Flowers M. C. , Penny D. E. , Pommelet J.‐C.
Published: January 2005

The kinetics of the gas‐phase decomposition of 1,2‐epoxycyclohexane has been studied over the temperature range 680–740 K at pressures between 1.6 and 6 torr. Isomerization to cyclohexanone and 2‐cyclohexen‐1‐ol accounts for ca. 97% of the primary reaction products and occurs by first‐order, homogeneous, nonradical processes:
Kinetics of the thermal gas phase isomerization of bicyclo[4.1.0]heptane
Authors: Flowers M. C. , Penny D. E.
Published: January 2005

The kinetics of the gas‐phase decomposition of bicyclo[4.1.0]heptane has been studied over the temperature range of 708–769 K at pressures between 1 and 17 torr. Isomerization to 1‐methylcyclohex‐1‐ene, methylenecyclohexane, and cycloheptene accounts for 96–98% of the primary reaction products and occurs by first‐order, homogeneous, nonradical processes.
Pyrolysis of 2,4‐dimethylhexene‐l and the stability of isobutenyl radicals
Authors: Tsang Wing
Published: January 2005

2,4‐Dimethylhexene‐l has been decomposed in single‐pulse shock tube experiments. Rate expressions for the initial reactions are

and

sec−1 at 1.5–5 atm and 1050°K. This leads to ΔH°f300 (CH2 = C(CH3)CH2) = 124 kJ/mol, or an allylic resonance energy of 50 kJ/mol. Rate expressions for the decomposition of the appropriate olefins which yield isobutenyl radicals and methyl, ethyl, isopropyl, n‐propyl, t‐butyl, and t‐amyl radicals, respectively, are presented. The rate expression for the decomposition of isobutenyl radical is

(at the beginning of the fall‐off region). For the combination of isobutenyl and methyl radicals, the rate constant at 1020°K is

Combination of this number and the calculated rate expression for 2‐methylbutene‐1 decomposition gives S. (1100) = 470 J/mol °K. This yields

It is demonstrated that an upper limit for the rate of hydrogen abstraction by isobutenyl from toluene is
Absolute rate constants for reactions of free radicals in the high‐temperature photolysis of formamide vapor. II. Amino radicals
Authors: Back R. A. , Yokota T.
Published: January 2005

The rotating‐sector method has been applied to the photoinitiated radical‐chain decomposition of formamide at 300°C to measure the rate constant for the bimolecular disappearance of NH2 radicals. The decomposition is propagated by the reactions (1)

(2)

Conditions were chosen so that reaction (1) was rate controlling and NH2 the terminating radical. A flow system was employed with C2F6 as a carrier gas at a pressure of 300 Tort, and the chain reaction was initiated by the photolysis of either formamide or NH3. A value of 4.7(±2.0) × 1010 (M ·sec)−1 was estimated for the termination reaction (3)

and a value of 8.4 × 106 (M ·sec)−1 for reaction (1) in the same system, both at 300°C.
Unexpectedly rapid vapor‐phase reaction between bromine and methyl iodide
Authors: Okafo E. N. , Whittle E.
Published: January 2005

The overall reaction (1)

occurs readily in the gas phase, even at room temperature in the dark. The reaction is much faster than the corresponding process

and does not involve the normal bromination mechanism for gas phase reactions. Reaction (1) is probably heterogeneous although other mechanisms cannot be excluded.

The overall reactions (1)

(2)

proceed, for all practical purposes, completely to the right‐hand side in the vapor phase. The expected mechanism is (3)

(4)

(5)

(6)

(7)

where reaction (3) is initiated thermally or photochemically. Reaction (4) is of interest because little kinetic data are available on reactions involving abstraction of halogen by halogen and also because an accurate determination of the activation energy E4 would prmit us to calculate an acccurate value of the bond dissociation energy D(CH3I).
The pyrolysis of 2‐nitrosoisobutane and the bond dissociation energies of nitroso compounds
Authors: Choo K. Y. , Mendenhall G. D. , Golden D. M. , Benson S. W.
Published: January 2005

Study of the reactionby very‐low‐pressure pyrolysis (VLPP) in the temperature range of 550–850°K yields for the high‐pressure Arrhenius parameterswhere θ = 2.303RTin kcal/mole. These in turn yield for the high‐pressure second‐order recombination oftBu + NO,k−1= (3.5 ± 1.7) × 1091./mole·sec at 600°K. For the competing reactionl./mole·sec andE4≥ 4.2 kcal/mole. The bond dissociation energyDHo(tBu‐NO) was determined to be (39.5 ± 1.5) kcal/mole, both from the equilibrium constant and from the activation energy of reaction (1), obtained from RRKM calculations. A ‘free‐volume’ model for the transition state for dissociation is consistent with the data. A limited study of the system at 8–200 torr showed an extremely rapid inhibition by products and a very complex set of products.
Addition of methyl radicals to carbon monoxide: Chemically and thermally activated decomposition of acetyl radicals
Authors: Watkins K. W. , Word William W.
Published: January 2005

Chemically activated acetyl radicals, with an excitation energy of 78 kJ/mole, were formed by the addition of methyl radicals to carbon monoxide. At 273·K the pressure required to stabilize one half of the excited radicals was 500 torr. From measurements of the acetyl radical yield at pressures in the range of 700–2100 torr, and at temperatures in the range of 260–413 K, extrapolations to infinite pressure yielded kinetic parameters for the addition of methyl radicals to carbon monoxide, and for the thermal decomposition of acetyl radicals. The rate constants were found to be log k[cm3 / (mole·s)] = 11.2–25(kJ/mole/2.3) RT, and log k(s−1) = 13.5−72 (kJ/mole)/2.3RT, respectively. Estimated thermochemical properties of the acetyl radical are ΔHfº = −17 kJ/mole and Sº = 262 J/K°mole.
The oxidation of cis‐ and trans‐CHClCHCl
Authors: Sanhueza Eugenio , Heicklen Julian
Published: January 2005

When Cl atoms react with CHClCHCl in the presence of O2 at 31°C, a long‐chain oxidation occurs. The products are the geometrical isomer of the starting olefin and CHClO, HCl, CO, and CCl2O. The quantum yields of the oxygen‐containing products are the same with both isomers and are Φ{CHClO} = 30, Φ{CO} = 11.7, and Φ{CCl2O} = 1.29. The chlorine atom adds to the olefin and is followed by O2 addition. The reaction then proceeds
equation image
with k6a/k6b = 19 and k7a/k7 ∼ 0.5, where k7 ≡ k7a + k7b. The CCl2H radical oxidizes to regenerate the chain carrier.

O(3P) reacts with CHClCHCl at 25°C with a rate coefficient of 6.6 × 108 M−1 sec−1 for trans‐CHClCHCl and 2.8 × 108 M−1 sec−1 for cis‐CHClCHCl. The reaction channels are
equation image
with k1a/k1 = 0.23 and 0.28, respectively, for the cis and trans compounds. Reaction (1b) occurs < 4% of the time. Reaction (1c) leads to polymer production and presumably, via redissociation, to the geometrical isomer of the starting olefin. In the presence of O2 the same long‐chain oxidation is observed as in the chlorine‐atom initiated oxidation. The chain‐initiating step is
Addition of methoxy radicals to olefins
Authors: Lissi E. A. , Massiff G. , Villa A.
Published: January 2005

The addition of methoxy radicals to several olefins has been studied by a competitive method at 127°C in gas phase. The thermal decomposition of dimethyl peroxide was used as methoxy radical source. The rate of addition to the double bond was measured relative to the oxidation of carbon monoxide. For the addition to ethylene it was obtained that

This rate constant is similar to the one shown by methyl radicals under similar conditions. From the relative rate of addition to several chlorinated and fluorinated olefins it can be concluded that methoxy radicals show very little “electrophilic” character.
Primary steps in the photolysis of cis‐1,2‐dichloroethylene
Authors: Ausubel R. , Wijnen M. H. J.
Published: January 2005

The photolysis of cis‐1,2‐dichloroethylene has been investigated in the presence of I2 as a function of incident wavelength and as a function of initial cis pressure. The results indicate that at ± > 2200Å the following primary processes occur:

The lifetime of the excited state yielding the above products is estimated at about 2.4×10−9 sec. At shorter wavelengths additional C2H2 is produced by decomposition of a vibrationally excited C2H2Cl radical.

Scavenging of the CHClCH radical by I2 produced trans and cis‐CHClCHl in a ratio of 4 to 1, respectively.
Abstraction of chlorine atoms from polychloroalkanes. II. Neighboring group effect on the rates of chlorine abstraction by cyclohexyl radicals
Authors: Katz M. G. , Rajbenbach L. A.
Published: January 2005

The kinetics of chlorine atom abstraction from trichloromethyl groups of the haloethanes (XCCl3), CF3CCl3, CH3CCl3, C2Cl6, C2Cl5H, and CH2ClCCl3, by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4.

The following Arrhenius parameters were obtained:
equation image
The error limits are the standard deviations from least mean square Arrhenius plots. It is shown that the neighboring group effect on the rate of chlorine atom abstraction from the trichloromethyl groups can be correlated with Taft polar substituent constants.
Chlorine‐photosensitized reactions in the Cl2 + O2 + 1,1,1,2‐C2H2Cl4 system
Authors: Gillotay D. , Olbregts J.
Published: January 2005

The gas‐phase photochlorination (λ = 436 nm) of the 1,1,1,2‐C2H2Cl4 has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps:

The dissociation energy D(CCl3CHClO2) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions
equation image

The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes.
Estimation of the R‐H bond energy from the activation energy for the reaction RH + O2 → R· + HO2·
Authors: Denisov E. T. , Denisova L. N.
Published: January 2005

Since the activation energy for the reaction RH + O2 → R· + HO2. is very close to its endothermicity, the R‐H bond energy can be calculated from the activation energy for free radical formation by the reaction RH + O2. The relation between Ei and QR–H was found empirically after measuring Ei by the method of inhibitors for the oxidation of cyclohexane, nheptane, and toluene:

The values of QR–H are calculated from these and earlier experimental data for five hydrocarbons, five phenols, and four aromatic amines.
The isothermal flash photolysis of hydrazoic acid
Authors: Paur Richard J. , Bair Edward J.
Published: January 2005

The flash photolysis of HN3 was studied by coordinated time‐resolved spectroscopic measurements of HN3 NH(a1Δ), NH(X3Σ), NH(c1π), NH(A3π), NH2, and N3 following flash photolysis of mixtures of HN3 with argon or helium. The primary photolysis is complex, but when the wavelength distribution of the flash is limited to values greater than about 200 nm, the major reactive product is NH(1Δ), or states which quickly decay to NH(1Δ). Disappearance of NH(1Δ) occurs predominantly by the process

The process has little, if any, energy of activation, and no detectable dependence on the pressure of inert gas below 1 atm. The rate of formation of NH2 in its ground vibrational state depends on the inert gas pressure in a way that can be accounted for by vibrational relaxation from initial excited vibrational states. The total amount of NH2 is roughly comparable with the amount of HN3 decomposed by primary photolysis. The observed N3 can be attributed to the NH(1Δ) + HN3 reaction, although a smaller amount could also be formed by primary photolysis. The value of k2 is revised upward from the value given in a preliminary report on the basis of a more careful consideration of the effects of Beer's law failure in absorption measurements involving narrow spectral lines.
Catalysis by HBr in the bromination of o‐xylene in acetic acid
Authors: Yesodharan E. P. , Rajaram J. , Kuriacose J. C.
Published: January 2005

Hydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr3 or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o‐xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o‐xylene with the orders in Br2 and HBr depending on the concentrations. A composite rate expression involving Br2 and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.
Flash photolysis study of the recombination of chlorine atoms in the presence of various inert gases and NO
Authors: Hippler H. , Troe J.
Published: January 2005

The recombination of chlorine atoms has been investigated by flash photolysis in the inert gases He, Ne, Ar, N2, CO2, CF4, SiF4, SF6, and C2F6. The pressure dependence of the reaction has been measured between 0.5 and about 100 atm for He, N2, and CO2. Experiments on the NO‐catalyzed recombination of chlorine in the presence of He (0.5–100 atm) permitted a determination of the falloff curve of the reaction Cl+NO(+He)→ClNO(+He).
Triplet excited states of nitronaphthalenes. II. b‐Nitronaphthalene
Authors: Capellos C. , Suryanarayanan K.
Published: January 2005

Nanosecond flash photolysis of b‐nitronaphthalene (b‐NO2C10H7) in nonpolar and polar solvents shows a transient species with maximum absorption and lifetime dependent on solvent polarity. In deaerated n‐hexane the absorption maximum and lifetime (1/k) are 425 nm and 530 nsec, while in deaerated ethanol the corresponding values are 470 nm and 1.7 ·sec. This transient absorption is attributed to the triplet excited state of b‐NO2C10H7, and the observed red shift as well as its longer lifetime in polar solvents are indicative of the intramolecular charge transfer character of this state. The change of dipole moment accompanying the transition T1 → Tn, as well as rate constants for electron and proton transfer reactions involving the T1 state of b‐NO2C10H7, were determined. The spectroscopic and kinetic data obtained in this work indicate that the triplet state of b‐NO2C10H7 behaves like a n‐π* state in nonpolar media, while in polar solvents the n‐π* character of the state is reduced with a simultaneous increase in the charge transfer character.
A shock‐tube study of the kinetics of reaction of hydroxyl radicals with H2, CO, CH4, CF3H, C2H4, and C2H6
Authors: Bradley J. N. , Capey W. D. , Fair R. W. , Pritchard D. K.
Published: January 2005

Concentration‐time profiles have been measured for hydroxyl radicals generated by the shock‐tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction

are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF3H:H2:CH4:C2H4:C2H6, respectively.
Lyman‐α absorption photometry at high pressure and atom density kinetic results for H recombination
Authors: Lynch K. P. , Schwab T. C. , Michael J. V.
Published: January 2005

Atomic absorption and fluorescence spectrophotometry have been routinely used in kinetic investigations as probes of relative, rather than absolute, atom concentration. The calibration of a Lyman‐α photometer for measurement of absolute hydrogen atom concentrations at levels [H] ι ≤ 1.8 × 1014 atoms/cm2 and total pressure of 1.5 torr He is described. The photometer is characterized in terms of a two‐level emission source and an absorption region in which only Doppler broadening of the transition is considered. The modifications due to pressure broadening by high pressures (500 ≤ P ≤ 1500 torr) in the absorption region are discussed in detail. Application of the technique is reported for the recombination of hydrogen atoms in the presence of six nonreactive heat bath gases. Experiments were performed in a static reaction cell at pressures of 500–1500 torr of heat bath gas, and hydrogen atoms were produced by Hg (3P1) photosensitization of H2. The technique is critically evaluated and the mechanistic implications of the hydrogen atom recombination results are examined. The measured room temperature recombination rate constants in H2, He, Ne, Ar, Kr, and N2 are 8.5 ± 1.2, 6.9 ± 1.5, 5.9 ± 1.5, 8.0 ± 0.8, 10.2 ± 0.9, and 9.6 ± 1.4, respectively, where the units are 1033 cm6/molec2 · sec.
Hydroxyl radical measurements in a photochemical reactor by laser‐induced fluorescence
Authors: Wu C. H. , Wang Charles C. , Japar S. M. , Davis L. I. , Hanabusa M. , Killinger D. , Niki H. , Weinstock B.
Published: January 2005

Measurements of hydroxyl radical (HO) concentrations in ambient air by the technique of laser‐induced fluorescence have been recently reported. The present study was undertaken to provide an independent test of the validity of those measurements. A photochemical reactor was used to provide a source of HO, and the concentration of HO in the reactor was determined by the laser‐induced fluorescence technique. The HO concentration was also deduced from measured hydrocarbon decay rates in the reactor. There was agreement between the HO concentrations obtained by these two different methods, thus providing further validation of the fluorescence method. Some studies of HO fluorescence efficiency as well as of possible interferences with the fluorescence measurements are reported.
The deprotonation of internally hydrogen‐bonded acids. Mechanistic conclusions from the influence of general bases
Authors: Perlmutter‐Hayman Berta , Shinar Ruth
Published: January 2005

The reactions between alizarin yellow G and six different bases B (including OH−) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature‐jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion‐controlled reaction between the base and that fraction which is present in the “open” non‐hydrogen‐bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge.

The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method.
Abstraction of chlorine atoms from polychloroethanes. IV. The kinetics of chlorine abstraction from 1,1,2‐trichloroethane, 1,1‐dichloroethane, and 1,2‐dichloroethane by cyclohexyl radicals
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A.
Published: January 2005

The kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2‐C2Cl3H3, 1,1‐C2Cl2H4, and 1,2‐C2Cl2H4 by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4. The following Arrhenius parameters were obtained:

E(EClH)‐

Temperature

A(ECLH)
E(CCl4)
log A(EClH)
E(EClH)
Range

log

EClH
A(C2Cl4)
(kcal/mol)
(1.mol·sec)
(kcal/mol)
(°C)

CHCL2CH2Cl
0.03 ± 0.08
3.87 ± 0.17
8.98 ± 0.14
11.17 ± 0.27
150 – 250

CHCL2CH3
0.13 ± 0.13
4.63 ± 0.27
8.18 ± 0.19
11.93 ± 0.37
130 – 250

CHCL2CH2Cl
0.50 ± 0.17
7.57 ± 0.35
9.18 ± 0.23
14.87 ± 0.45
150 – 250

The error limits are the standard deviations from least mean square Arrhenius plots.

The α and ß activation effects on the kinetics of Cl atom abstraction from chloroalkanes are discussed. From the linear relation between the relative reactivities of cyclohexyl radicals toward the XCCl3 and XCHCl2 series, ECl(c‐C6H11· + CHCl2CHCl2) = 10.2 ± 1 kcal/mol and ECl(c‐C6H11· + CHCl22CCl3) = 9.7 ± 1 kcal is derived.
Equilibrium, kinetics, and mechanism of the malonic acid–iodine reaction
Authors: Leopold Kenneth R. , Haim Albert
Published: January 2005

The equilibrium constant for the reaction CH2(COOH)2 + I3− ⇆ CHI(COOH)2 + 2I− + H+, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO4), is (2.79 ± 0.48) × 10−4M2. Stopped‐flow kinetic measurements at 25°C and ionic strength 1.00M with [H+] = (2.09‐95.0) × 10−3M and [I−] = (1.23‐26.1) × 10−3M indicate that the rate of the forward reaction is given by (k1[I2] + k3[I3−]) [HOOCCH2COO−] + (k2[I2] + k4[I3−]) [CH(COOH)2] + k5[H+] [I3−] [CH2(COOH)2]. The values of the rate constants k1‐k5 are (1.21 ± 0.31) × 102, (2.41 ± 0.15) × 101, (1.16 ± 0.33) × 101, (8.7 ± 4.5) × 10−1M−1·sec−1, and (3.20 ± 0.56) × 101M−2·sec−1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by ken[CH2(COOH)2], with ken = 2.0 × 10−3 + 1.0 × 10−2 [CH2(COOH)2]. An intramolecular mechanism, featuring a six‐member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.
The production and subsequent relaxation of vibrationally excited OH in the reaction of atomic oxygen with HBr
Authors: Spencer John E. , Glass G. P.
Published: January 2005

A fast discharge flow apparatus equipped for EPR detection of radicals has been used to investigate the reaction O + HBr → OH + Br. At 295°K, measurements showed that more than 97% of all OH produced in this reaction was formed initially in its first vibrationally excited state. Rate constants for physical deactivation of OH(v = 1) by O(3P), Br(2P3/2), H2O, and HBr were measured as (1.45 ± 0.25) × 10−10, (6.4 ± 2.4) × 10−11, (1.35 ± 0.50) × 10−11, and < 10−12 cm3/molec·sec, respectively.
The gas‐phase pyrolysis of alkyl nitrites. IV. Ethyl nitrite
Authors: Batt L. , Milne R. T. , McCulloch R. D.
Published: January 2005

The rate of decomposition of methyl nitrite (MN) has been studied in the presence of isobutane‐t‐BuH‐(167‐200°C) and NO (170‐200°C). In the presence of t‐BuH (∼0.9 atm), for low concentrations of MN (∼10−4M) and small extents of reaction (4‐10%), the first‐order homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k4(t‐BuH) »k2(NO): . The results indicate that the termination process involves only \documentclass{article}\pagestyle{empty}\begin{document}$ t - {\rm Bu\, and\, NO:\,\,}t - {\rm Bu} + {\rm NO\stackrel{e}{\longrightarrow}} $\end{document} products, such that ke ∼ 1010 M−1 ∼ sec−1.Under these conditions small amounts of CH2O are formed (3‐8% of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence at low pressures of t‐BuH. Addition of large amounts of NO completely suppresses MeOH formation.

The rate constant for reaction (1) is given by k1 = 1015.8°0.6‐41.2°1/· sec−1. Since (E1 + RT) and ΔHΔ1 are identical, within experimental error, both may be equated with D(MeO ‐ NO) = 41.8 + 1 kcal/mole and E2 = 0 ± 1 kcal/mol. From ΔS11 and A1, k2 is calculated to be 1010.1°0.6M−1 · sec−1, in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k6/k2 = 0.17 independent of temperature, we conclude that \documentclass{article}\pagestyle{empty}\begin{document}$ E_6 = 0 \pm 1{\rm kcal}/{\rm mol\, and\,}\,k_6 = 10^{9.3} M^{- 1} \cdot {\rm sec}^{- 1} :{\rm MeO} + {\rm NO}\stackrel{6}{\longrightarrow}{\rm CH}_2 {\rm O} + {\rm HNO} $\end{document}. From the independent observations that k2:k2→: k6→ was 1:0.37:0.04, we find that k2→ = 109.7M−1 ċ sec−1 and k6→ = 108.7M−1 ċ sec−1. In addition, the thermodynamics lead to the result

In the presence of NO (∼0.9 atm) the products are CH2O and N2O (and presumably H2O) such that the ratio N2O/CH2O ∼ 0.5. The rate of CH2O formation was affected by the surface‐to‐volume ratio s/v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CH2O arises as the result of an essentially homogeneous first‐order, fourcenter elimination of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HNO}:{\rm MN\stackrel{5}{\longrightarrow}CH}_{\rm 2} {\rm O} + {\rm HNO} $\end{document}. The rate of CH2O formation is given by k5 = 1013.6°0.6‐38.5‐1/ċ sec−1.
Pyrolysis of trifluoroacetaldehyde. The formation of trifluoromethane and hexafluoroethane
Authors: Liu Michael T. H. , Loucks Leon F. , Hooper David G.
Published: January 2005

The thermal decomposition of trifluoroacetaldehyde at temperatures f 471 to 519°C has been studied by measuring the rates of formation of CF3H and C2F6. It is concluded that the high‐pressure reaction mechanism involves a Rice‐Herzfeld reaction scheme with first‐order initiation and second‐order termination via CF3 combination. However, a falloff in reaction rates is observed at pressures below 100 mmHg. The Arrhenius parameters of the three rate constants corresponding to the overall reaction, the initiation reaction, and an abstraction reaction have been evaluated.
Radical equilibrium studies; the thermodynamic parameters of n‐propyl
Authors: Marshall Roger M. , Rahman Lutfor
Published: January 2005

A novel method for the investigation of the thermodynamic properties of free radicals is described. It involves the establishment of an equilibrium of the form

where R1 and R2 are free radicals, and the measurement of the recombination products of R1 and R2. The method is applied to the case where R1 is n‐propyl, R2 is methyl, and the olefin is ethene, using the thermal decomposition of azomethane (a source of methyl) in the presence of ethene in the temperature range of 581–649°K. Using the best available thermodynamic parameters for methyl, it is concluded that those for n‐propyl are in need of adjustment. We recommend the values ΔHf°(300°K) = 22.6 ± 1 kcal/mol and S300° = 67.4 ± 3 cal/mol · K together with either the heat capacity data of O'Neal and Benson or the essentially identical data derivable from the results of Purnell and Quinn.
Shock‐tube study of thermal decomposition of propene in the presence of deuterium
Authors: Yano Takayuki
Published: January 2005

The thermal decomposition of propene in the presence of D2 was studied in a single‐pulse shock tube in the temperature range of 1200–1400°K. The main decomposition products were methane, ethylene, allene, and propyne. Furthermore, deuterated species were observed of each product and of propene, with characteristic compositions that were dependent on propene conversion. Geometrical isomers of monodeuterated propene, as the result of H‐D exchange, were analyzed by microwave spectroscopy. From these observations, the reactivities of n‐ and isopropyl radicals at high temperatures were determined. The former was found to be an intermediate of methane and ethylene and the latter was found to be responsible for the formation of the deuterated propene as follows:
equation image

The rate constant ratio kn/ki was estimated to be 0.5–0.8, which was more than ten times greater than that obtained at room temperature. It was also found that allene or propyne was produced from allyl radicals and that acetylene was produced from vinyl radicals. In addition, the rate constant of the hydrogen abstraction by the hydrogen atom from C3H6 was found to be six times greater than that by the hydrogen atom from D2.
Reactions of the iso‐butyl radical during 1,1′‐azoisobutane pyrolysis
Authors: McKay G. , Turner J. M. C.
Published: January 2005

Quantitative analysis of the products formed in 1,1′‐azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso‐butyl radical are
equation image
Analysis of initial rate data gave log10k4/(kc)1/2(cm−3/2.mol 1/2.sec−1/2) = 7.54±0.44 − (136.5 + 4.8) kJ/mol/2.303RT, the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of ka/(kc)1/2 where ka is the rate constant of the reaction iC4H9 + AIB → iC4H10 +. AIB were consistent with published parameters determined by photolysis of 1,1′‐azoisobutane. Combination of photolysis and pyrolysis data gave log10 ka/(kc)1/2(cm3/2.mol−1/22.sec−1/2) = 3.68 ± 0.15 − (27.2 ± 1.2) kJ/mol/2.303RT. The crosscombination ratio for methyl and iso‐butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso‐butyl radicals.
Kinetics of the gas‐phase reaction between iodine and trifluorosilane and the bond dissociation energy D(F3SiH)
Authors: Doncaster Alan M. , Walsh Robin
Published: January 2005

The title reaction has been investigated in the temperature range 667–715K. The only reaction products were trifluorosilyl iodide and hydrogen iodide. The rate law

was obeyed over a wide range of iodine and trifluorosilane pressures. This expression is consistent with an iodine atom abstraction mechanism and for the step

log k1(dm3/mol·sec) = (11.54 ± 0.17) − (130.5 ± 2.2 kJ/mol)/RT In 10 has been deduced. From this the bond dissociation energy D(F3SiH) = (419 ± 5) kJ/mol (100.1 kcal/mol) is obtained. The kinetic andthermochemical implications of this value are discussed.
Ene reactions of olefins, part II. The addition of ethylene to propylene and to isobutene and the addition of propylene to propylene
Authors: Richard C. , Back M. H.
Published: January 2005

The pyrolysis of ethylene–propylene and ethylene–isobutene mixtures has been studied in a static system over the temperature range of 682°–754° K and for initial pressures of each olefin of 33–300 torr. The following molecular ene reactions were observed and the rate constants measured:
equation image
Using thermodynamic data, rate constants for the corresponding retro‐ene decomposition reactions were calculated and compared to kinetic data reported for similar compounds. Other products were formed by radical chain processes, the main higher molecular weight ones being cyclopentene and 1‐methylcyclopentene. A mechanism involving addition of allyl radicals is suggested for the formation of these products.
Recombination of carbon monoxide and oxygen atoms
Authors: Hardy J. E. , Gardiner W. C. , Burcat A.
Published: January 2005

The recombination of carbon monoxide and oxygen atoms was studied in reflected shock waves in H2:O2:CO:Ar = 0.1:1:24:75 with 1300 < T5 2200 K and 2 < P5 < 4 atm. Reaction progress was monitored by observations of the carbon monoxide flame spectrum near 435 nm and carbon dioxide thermal emission near 4.2 μm. Data analysis was accomplished with the aid of computer modeling using a 27‐reaction mechanism. Computer modeling experiments also showed that these measurements were sensitive primarily to the rate of the reaction CO + O + M = CO2 + M and only slightly sensitive to the rates of other reactions. The best fit to the data was achieved with a rate constant for this reaction of 7.7 × 10−35 exp[19 kJ/RT] cm6 s for the temperature range of these experiments. Correlation of this result and previous data covering the temperature range 250 < T < 11,000 K confirms that this recombination reaction is governed by a nonadiabatic curve crossing with an activation barrier of about 20 kJ and subsequent deactivation of a singlet CO2 molecule.
Rate constant and activation energy for the gaseous reaction between hydroxyl and formaldehyde
Authors: Smith Roland H.
Published: January 2005

The rate constant k4 has been measured at 268°, 298°, and 334° K for the reaction CH2O + 2OH → CO + 2H2O relative to that for OH + OH (k2) by competition experiments in a discharge flow tube using mass‐spectrometric analysis. Based on k2 = 2.24 × 10−12cm3/molec·sec at 298°K and E2 = 4 kJ/mol, k4 = (6.5 ± 1.5) × 10−12cm3/molec·sec at 298°K and E4 = (6 ± 2)kJ/mol.
The quantum efficiency of the primary processes in formaldehyde photolysis at 3130 Å and 25°C
Authors: Horowitz Abraham , Calvert Jack G.
Published: January 2005

The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1–12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O +hν → H + HCO (1): CH2O +hν → H2+ CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCOand Φ. The ratio ΦCO/Φwas found to be 1.01 ± 0.09(2σ) and (Φ+ ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12‐fold change in incident light intensity. Isobutene and nitric oxide additions reduced Φto about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/Φreached a limiting value of 2.3; with NO addition ΦCOexceeded unity. The addition of small amounts of Me3SiH reduced Φto 1.02 ± 0.08 and lowered ΦCOto 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with ϕ2= 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with ϕ1= 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)–(5): H + CH2O → H2+ HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2+ 2CO (5). The data suggestk4/k5≅ 5.8. Isobutene reduced Φby the reaction H +iso‐C4H8→ C4H9(20), and the results givek20/k3≅ 43 ± 4, in good agreement with the ratio of the reported values of the individual constantsk3andk20.
The decomposition kinetics of chemically activated methyl‐d1‐methylsilane‐d2 and ethylsilane‐d3
Authors: Richardson T. H. , Simons J. W.
Published: January 2005

The decomposition kinetics of chemically activated methyl‐d1‐methylsilane‐d2 (DMS‐d) and ethylsilane‐d3 (ES‐d) from the Si‐D and C‐H insertion reactions of CH2 (1A1) with methylsilane‐d3 have been studied. The total rate constants for decomposition of chemically activated DMS‐d3 and ES‐d3 have been measured. The individual rate constants for molecular elimination of CH3D, CH2D2, and D2 from DMS‐d and for molecular elimination of CH3CH2D and D2 from ES‐d have been measured. All of the above rate constants exhibit the expected kinetic isotope effect when compared to those found previously in the undeuterated system. RRKM theory calculations of the rate constants for the expected C‐Si and Si‐D bond rupture processes, based on energetics and activated comple× models deduced previously for the undeuterated system, were carried out. In the case of DMS‐d the RRKM theory calculations of rate constants for the bond rupture processes combined with experimental rate constants for the molecular elimination processes gave a total rate constant for decomposition in agreement with the measured value. The results of a high‐pressure study of the CH3D/CH2D2 ratio from chemically activated DMS‐d3 decomposition were consistent with complete randomization of internal energy up to a pressure of 4 atmospheres (lifetime of ∼1.7 × 10×11 sec). This is not an unexpected result in light of earlier work.
Molecular beam sampling
Authors: Colussi A. J. , Benson S. W.
Published: January 2005

Beam attenuation and mass discrimination in effusive and quasieffusive molecular beams of gaseous mixtures have been studied experimentally in an instrument of conventional design, and have been rationalized in terms of transition flow effects and elastic scattering. Their implication in the quantitative monitoring of reacting chemical systems is examined, with particular emphasis in the case of the very‐low‐pressure pyrolysis technique.
Kinetics and mechanism of acetylacetonate transfer from acetylacetonatomanganese(III) to iron(III) in acetonitrile catalysis and inhibition effects
Authors: Schmid Roland , Sapunov Valentin N.
Published: January 2005

The reaction between tris(acetylacetonato)magnanese(III) and hexa(N,N‐dimethylformamide)iron(III) perchlorate in acetonitrile proceeds in two stages. The first stage corresponds to the reaction of pentacoordinated Fe(DMF) with Mn(acac)3, and the rate‐determining step of the second stage consists mainly in the elimination of a DMF ligand from Fe(DMF) to yield Fe(DMF) which reacts rapidly with the manganese complex. The formation of Fe(DMF) is catalyzed by Mn(acac)3, this catalytic effect being decreased by manganese products. The rate‐determining step for the formation of Fe(acac)3 is the transfer of the first acetylacetonate to yield Fe(acac)2+. The final products of iron depend on the ratio of reactant concentrations. With Mn or Fe in excess, Fe(acac)3 or Fe(acac)2+ are mainly produced.
Neighboring group participation of polar β substituents in the gas‐phase pyrolysis of 2‐substituted ethyl chlorides
Authors: Chuchani Gabriel , Martin Ignacio , Martin Gonzalo , Bigley David B.
Published: January 2005

The pyrolysis of 2‐dimethylaminoethyl chloride in the temperature range of 360–400°C and the pressure range of 60–271 mmHg is a homogeneous, unimolecular, first‐order reaction giving dimethylvinyl amine and hydrogen chloride. 2‐Methoxyethyl chloride pyrolysis in the temperature range of 450–490°C and the pressure range of 53–110 mmHg by a similar unimolecular, first‐order reaction yields methylvinyl ether and hydrogen chloride. These reactions were carried out in a seasoned reaction vessel and in the presence of a propene inhibitor. The methylvinyl ether decomposes slowly into other products at the temperature of pyrolysis. The rate constants are given by the Arrhenius equations

(a) 2‐dimethylaminoethyl chloride:

(b) 2‐methoxyethyl chloride:

The effects of polar β substituents in the 2 position of ethyl chloride are discussed in terms of anchimeric assistance and electron‐withdrawing deactivation in these elimination reactions. The present results are consistent with the heterolytic nature of the four‐centered cyclic transition state for the gas‐phase pyrolysis of alkyl halides.
Evaluation of boundary‐layer effects in shock‐tube studies of chemical kinetics
Authors: Fujii Nobuyuki , Koshi Mitsuo , Ando Hiromitsu , Asaba Tetsuro
Published: January 2005

Particle times of flight in incident shock flow were determined experimentally by marking several positions of the test gas (mainly Ar) in the shock tube with an infrared emitting gas (NO or CO2). From the local particle velocity, derived from the particle flight times, temperature and pressure changes behind the shock front were evaluated. Several experimental data were found to be correctly described by Mirels's formulations when used properly. The limitations of the formulations are discussed. It is found to be advisable to evaluate boundary‐layer effects on shock‐tube flow by experiments, rather than theory, in carrying out chemical kinetics studies.