Showing papers on "Reaction rate constant published in 1972"
TL;DR: In this paper, the temporal correlations of thermodynamic concentration fluctuations have been measured in a chemically reactive system at equilibrium by observing fluctuations of the fluorescence of a reaction product, and the experiment yields the chemical rate constants and diffusion coefficients and shows the coupling among them.
Abstract: The temporal correlations of thermodynamic concentration fluctuations have been measured in a chemically reactive system at equilibrium by observing fluctuations of the fluorescence of a reaction product. The experiment yields the chemical rate constants and diffusion coefficients and shows the coupling among them. Data are reported for binding of ethidium bromide to DNA.
1,733 citations
TL;DR: The experiments show that an isomerization of DNA with a certain base sequence is possible in solution and the proposed model suggests a plausible mechanism.
1,035 citations
TL;DR: EDTA had no effect on the enzyme-catalyzed dismutation of superoxide radicals, but did eliminate catalysis by Cu++, and Boiling the enzyme or reversibly removing its copper prosthetic group caused loss of catalytic activity.
470 citations
TL;DR: Investigation of superoxide dismutase activity of bovine erythrocuprein by pulse radiolysis under steady-state and pre-steady-state conditions confirmed that enzyme turnover is effectively diffusion-limited.
300 citations
TL;DR: In this paper, the authors presented numerical quantum mechanical scattering calculations for the collinear H+H2 reaction on a realistic potential energy surface with an 0.424 eV (9.8 kcal) potential energy barrier.
Abstract: We present numerical quantum mechanical scattering calculations for the collinear H+H2 reaction on a realistic potential energy surface with an 0.424 eV (9.8 kcal) potential energy barrier. The reaction probabilities and rate constants are believed to be accurate to within 2% or better. The calculations are used to test the approximate theories of chemical dynamics. The reaction probabilities for ground vibrational state reagents agree well with the vibrationally adiabatic theory for energies below the lowest threshold for vibrational excitation, except when the reaction probability is less than about 0.1. For these low reaction probabilities no simple one-mathematical dimensional theory gives accurate results. These low reaction probabilities occur at low energy and are important for thermal reactions at low temperatures. Thus, transition state theory is very inaccurate at these low temperatures. However, it is accurate within 40% in the higher temperature range 450–1250°K. The reaction probabilities for hot atom collisions of ground vibrational state reagents with translational energies in the range 0.58 to 0.95 eV agree qualitatively with the predictions of the statistical phase space theory. For vibrationally excited reagents the vibrational adiabatic theory is not accurate as for ground vibrational state reagents. The lowest translational energy of vibrationally excited reagents above which statistical behavior manifests itself is less than 1.0 eV.
221 citations
TL;DR: The rate constants for the abstraction of a hydrogen atom from a wide variety of organic substrates at 30° have been correlated with the strength of the C-H bond that are broken, D[R-H].
Abstract: The rate constants, kp, for the abstraction of a hydrogen atom from a wide variety of organic substrates at 30° have been correlated with the strengths of the C—H bond that are broken, D[R—H] (in u...
221 citations
TL;DR: In this article, the authors used resonance absorption to monitor the removal of OH radicals following flash photolysis of mixtures containing H2O or N2O + H2.
Abstract: The rates of the reactions of OH with CO, C2H4 and C2H2 have been determined between 210 K and 460 K using time-resolved resonance absorption to monitor the removal of OH radicals following their creation by flash photolysis of mixtures containing H2O or N2O + H2. At 300 K, the rate constant, k6, for OH + CO → CO2+ H (6) is 8.7 × 1010 cm3 mol–1 s–1; k6 shows a slight positive temperature dependence, but the Arrhenius plot appears to be slightly curved. The nature of the path of this reaction is discussed and the results of transition state calculations are shown to agree well with the experimental data and to predict marked curvature in the Arrhenius plot above 500 K. The rate constants, k9 and k10, for the primary reactions of OH with C2H4 and C2H2 also increase only very slowly with temperature but, in these cases, the experimental results for 210 K ⩽T⩽ 460 K do fit Arrhenius expressions (energies of activation in kJ mol–1): k9= 4.5 × 1012 exp[– 0.9/RT] cm3 mol–1 s–1. k10= 1.2 × 1012 exp[– 2.1/RT] cm3 mol–1 s–1.
196 citations
TL;DR: In this paper, it was shown that HO2 radicals were produced in the gas phase by flash photolysis of water vapor (3%) in an atmosphere of hydrogen, helium, or argon containing ∼ 2% oxygen.
Abstract: HO2 radicals were produced in the gas phase by flash photolysis of water vapor (3%) in an atmosphere of hydrogen, helium, or argon containing ∼ 2% oxygen. Water is dissociated in the first continuum to H and OH, and O2 converts the H atoms to HO2. Hydrogen nearly doubles the amount of HO2 produced by converting OH to H. The absorption spectrum of HO2 is a broad band with a peak at 2050 A. The molar extinction coefficient, emax, based on measurement of the H2O2 formed in the hydrogen system, is 1770 ± 150 M−1· cm−1. The rate constant for the bimolecular combination reaction, HO2+HO2 → H2O2 + O2, was evaluated as 5.7 ± 0.5 × 109 M−1· sec−1 at 298°K and for the reaction HO2+OH→ H2O+O2, k = 1.2 ± 0.2 × 1011M−1. sec−1. From auxiliary measurements of the rate of O3 formation it was also found that, in the flash photolysis of O2 (2%) in H2, hot O atoms react with H2 to form OH and H which are then converted to HO2.
175 citations
TL;DR: The absorption spectrum of the hydroperoxyl radical (HO2) has been obtained by the molecular-modulation technique as discussed by the authors, and the rate constant for the disproportionation reaction HO2+HO2→ H2O2+O2 was found to be 3.5× 10−12
Abstract: The absorption spectrum of the hydroperoxyl radical (HO2) has been obtained by the molecular‐modulation technique. The radical was formed by the photolysis of hydrogen peroxide at 2537 A, by the photolysis of ozone in the presence of hydrogen peroxide at 2537 A, and by the photolysis of Cl2 in the presence of hydrogen peroxide at 3500 A. The vibrational frequencies of HO2 have been observed to be 1095, 1390, and 3410 cm−1. Details of the vibrational spectrum are consistent with the molecular geometry: H–O bond distance 0.96 A, O–O bond distance 1.3 A, and H–O–O angle approximately 108°. The absorption spectrum of HO2 in the ultraviolet has a maximum at 2100 A. Kinetic analysis of the modulated absorption signals shows that the HO2 radical decays by a process second order in HO2 concentration. The rate constant for the disproportionation reaction HO2+HO2→ H2O2+O2 was found to be 3.6± 0.5× 10−12 cm3/molecule· sec in agreement with a reported value of 3× 10−12 cm3/molecule· sec. The absorption cross section ...
162 citations
TL;DR: In this paper, Trajectory calculations were made using various types of modified London-Eyring-Polanyi-Sato (LEPS) surfaces to obtain the vibrational energy level distributions for comparison with experimental results.
Abstract: The reaction of atomic hydrogen with molecular fluorine produces vibrationally excited hydrogen fluoride with v′ ⩽ 8>. Maximum population is achieved in v′ = 6. It is estimated that 58 per cent of the available energy of reaction is initially present as HF v′→0 †. Trajectory calculations have been made using various types of modified London-Eyring-Polanyi-Sato (LEPS) surfaces to obtain the vibrational energy level distributions for comparison with experimental results. A general conclusion is that in all cases, the predicted distribution is too narrow. No one surface could simultaneously give an entirely satisfactory prediction of the product vibrational energy distribution, activation energy with related rate constant and reaction enthalpy. It is concluded that a systematic method of selection of the value for De 3 for the first 3Σ state will be necessary if a surface is to be transferred between related reactions. A ‘best’ surface is selected and shown to be compatible with the known activation energy a...
TL;DR: In this paper, current/potential curves have been obtained for the ferrous/ferric reaction at a rotating disc electrode in background electrolytes of 1 M HClO4, 0.5 M H2SO4 and 0.4 M KHSO4.
TL;DR: A conformational change accompanying azide binding is proposed that facilitates the subsequent initial weak binding of cyanide (K′α (inpresenceofN3−) = 0.7 mM) and the rate limiting step at high cyanide concentrations has the same velocity in the precence as in the absence of azide.
TL;DR: The new spectral species is interpreted to be an oxygenated form of cytochrome P-450, presumably a ternary complex of oxygen, camphor, and ferrous cyto Chrome, and undergoes slow decomposition to the ferric form of the hemoprotein and is most stable in the pH range 7–8 and at temperatures below 10 °.
TL;DR: In this paper, a theoretical study of current-potential curves in thin layer linear potential sweep voltammetry is presented for a reversible electrochemical reaction O+ ne R coupled with an irreversible chemical reaction.
TL;DR: The spontaneous and pepsin-catalyzed activation of peptinogen has been observed and analyzed kinetically as discussed by the authors, showing that the first-order reaction occurs in the pH range 1 to 3, implying an intramolecular activation mechanism.
TL;DR: In this article, the authors measured the oxygen uptake of clean nickel from 24° to 450°C at oxygen pressures of. Ultra high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. This was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8-30Aa.
Abstract: The oxidation of "clean" nickel has been investigated from 24° to 450°C at oxygen pressures of . Ultra‐high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. Oxygen uptake was measured manometrically with a capacitance gauge of submonolayer sensitivity. Initial rapid oxygen adsorption (and place exchange) on nickel was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8–30Aa. Growth of thicker films was in accord with a parabolic rate law, transport through the oxide occurring predominantly via easy diffusion paths. The value of 41 kcal·mole−1 calculated from an Arrhenius plot of the parabolic rate constants from 300° to 450°C is an approximate measure of the activation energy for growth via leakage paths. A p1/6 dependence of the parabolic growth rate on oxygen pressure was found at 450°C.
TL;DR: In this article, the Fischer-Tropsch reaction over triply promoted iron catalyst was studied in a differential reactor at 240 °C, in the pressure range 10 to 20 bar with synthesis gases of H2CO ratio varying from 1 to 7.
TL;DR: Use of the diffusion-controlled limit shows that p-cresol reacts in the unionized form over the experimental pH range, and that electrostatic interactions are therefore not responsible for the degree of complexity of the pH log rate profile.
TL;DR: In this article, the Elovich Equation was used to describe the kinetics of isotopic exchange of phosphate between 32P-labeled dilute orthophosphate solutions and Fe(III) phosphate complexes on the surfaces of goethite (α-FeOOH) crystals in dilute suspension.
TL;DR: In this paper, a curve crossing model for polyatomic molecules and a simple Landau-Zener calculation at thermal energies are briefly discussed, with the difficulties of using a curve-crossing model for molecular data and the difficulty of computing the rate constants for single electron transfer of polyatomic neutrals.
Abstract: Thermal energy reaction rate constants are reported for the partial charge‐transfer reactions Ca2+ + NO → Ca+ + NO+ and Mg2+ + X → Mg+ + X+ with X as Xe, NO, O2, N2O, CO2, CO, SO2, NH3, and NO2. The rate constants for single electron transfer of polyatomic neutrals are often three orders of magnitude larger than the rate of electron transfer from Xe. Within a curve crossing model the molecular data yield approximate efficiencies of electron transfer from 2.5 to 14.4 A. The difficulties of using a curve crossing model for polyatomic molecules and a simple Landau—Zener calculation at thermal energies are briefly discussed.
TL;DR: Theoretical treatment of both the molecular and atomic mechanisms for the hydrogen-iodine exchange reaction (H2+I2→ 2HI) is accomplished by means of extensive classical trajectories calculated on a reasonable potential energy surface in which the single adjustable parameter is the iodine core effective charge as discussed by the authors.
Abstract: Theoretical treatment of both the molecular and atomic mechanisms for the hydrogen‐iodine exchange reaction (H2+I2→ 2HI) is accomplished by means of extensive classical trajectories calculated on a reasonable potential‐energy surface in which the single adjustable parameter is the iodine‐core effective charge. The analysis shows the molecular mechanism to be dynamically forbidden, but gives an over‐all rate constant for the atomic mechanism in substantial agreement with the experimental values. The formation of a weak H2I complex is predicted to play an important dynamical role if the atomic mechanism is limited to reactions with collision complexes involving no more than two hydrogen atoms and two iodine atoms. Excellent agreement with experiment is obtained for the rate constant for the recombination I+I+H2→ I2+H2 and its negative temperature coefficient. Trajectories for the latter reaction are rich in multiple exchange of internal energy between the molecular species, but the formation of H2I is predi...
TL;DR: In this article, it was shown that the mechanism of the oxidation of ferrous ions is though to consist of simple electron transfer, and the difference in rate between H2O and D2O solution is attributed to differences between free energies of hydration in the two solvents.
Abstract: Hydroxyl radicals have been found by pulse radiolysis to oxidize hydrated ferrous to ferric ions with a rate constant of (2.3 ± 0.2)× 108 M–1 s–1. The corresponding reaction of OD radicals in D2O solution has a rate constant of (9.4 ± 0.8)× 107 M–1 s–1. OD radicals oxidize ferrocyanide in D2O solution with (9.7 ± 1.0)× 109 M–1 s–1. The mechanism of the oxidation of ferrous ions is though to consist of simple electron transfer, and the difference in rate between H2O and D2O solution is attributed to differences between free energies of hydration in the two solvents.
TL;DR: In this paper, the effect of ternary additions on the rate of coarsening of cementite in steel is considered in detail and a rate equation for the change in size of individual particles is derived using a crude model to estimate the diffusion.
TL;DR: In this paper, an analytical solution for the dispersion of a solute in a liquid flowing between two parallel plates in the presence of an irreversible first-order chemical reaction is presented.
Abstract: The paper presents an analytical solution for the dispersion of a solute in a liquid flowing between two parallel plates in the presence of an irreversible first-order chemical reaction. The effects of both homogeneous and heterogeneous reactions on the dispersion are studied under isothermal conditions. It is found that for homogeneous reaction in the bulk of the liquid, the effective Taylor diffusion coefficient decreases with increase in the reaction rate constant. Further for heterogeneous reaction at the catalytic walls, Taylor diffusion coefficient is also found to decrease with increase in the wall catalytic parameter for fixed reaction rate constant corresponding to the bulk reaction.
TL;DR: In this article, the reaction sequence leading from O2+ to H3O+· H2O was examined in He, Ar, N2, and O2 carrier gases in a flowing afterglow system.
Abstract: The reaction sequence leading from O2+ to H3O+· H2O was examined in He, Ar, N2, and O2 carrier gases in a flowing afterglow system. The rate constants for the reactions were measured and the kinetic analysis for their determination is presented. For M=N2, two new steps involving the formation and reaction of O2+· N2 were proposed and examined. The rate constants are discussed and compared with other experimental values.
TL;DR: In this article, the rate constants for reaction of the electron with biphenyl, carbon tetrachloride and oxygen in alkanes have been measured, and are found to be much larger than the values quoted in polar solvents.
Abstract: Electrons are produced in several organic liquids by the two‐photon laser photolysis of dilute solutions of anthracene and pyrene in these liquids. The rate constants for reaction of the electron with biphenyl, carbon tetrachloride and oxygen in alkanes have been measured, and are found to be much larger than the values quoted in polar solvents. The rate constants for reaction of the electron with biphenyl increase with the square root of the electron mobility while the corresponding reaction with O2 is independent of the electron mobility. The mobility of the electron in hydrocarbon mixtures follows the exponential of the mole fraction of the hydrocarbon with the higher mobility. Complex behavior is observed in alcohol‐hydrocarbon mixtures, which may be explained in terms of aggregates of alcohol in these mixtures. The data are discussed in terms of the present theories of the state of electrons in liquids.
TL;DR: Rate coefficients have been measured over the temperature range 250–370°K for the three‐body recombination of O(3P) with CO and earlier results at 300°K were found to have been influenced by unknown impurities in the CO, which have now been removed by more elaborate purification methods.
Abstract: Rate coefficients have been measured over the temperature range 250–370°K for the three‐body recombination of O(3P) with CO Earlier results at 300°K have been re‐evaluated and were found to have been influenced by unknown impurities in the CO, which have now been removed by more elaborate purification methods For CO as the third body, the rate constant is given by k = 65 × 10−33 exp(−4340 ± 550/RT) cm6 molecule−2·sec−1 For N2 and CO2, the 296°K rate constants are 23 and 62 × 10−36 cm6 molecule−2·sec−1, respectively
TL;DR: Analysis of albumin which has reacted with p-nitrophenyl acetate indicate that two tyrosyl hydroxyl groups on the protein are rapidly acetylated by the ester.
TL;DR: In this paper, the authors measured the thermal energy rate constants for the charge transfer of CO+ with O and NO at 300°K and 3.3 × 10−10 cm3/sec.
Abstract: Thermal energy rate constants for the charge transfer of CO+ with O and NO have been measured to be 1.4 and 3.3 × 10−10 cm3/sec at 300°K. The rate constants for H+ with O and NO are 3.8 and 19 × 10−10 cm3/sec. The H+ + O charge‐transfer data agree remarkably well with the value extrapolated from crossed‐beam studies at much higher energies.