The temperature-dependence of elementary reaction rates: beyond Arrhenius

2008 ◽  
Vol 37 (4) ◽  
pp. 812-826 ◽  
Author(s):  
Ian W. M. Smith
Keyword(s):  
Temperature Dependence ◽  
Reaction Rates ◽  
Elementary Reaction

Nanoparticles Size in Fe73.5Cu1Mo3Si13.5B9 Melt

2020 ◽  
Vol 861 ◽  
pp. 107-112
Author(s):  
Vladimir S. Tsepelev ◽  
Yuri N. Starodubtsev ◽  
Kai Ming Wu ◽  
Yekaterina A. Kochetkova
Keyword(s):  
Experimental Data ◽  
Diffusion Coefficient ◽  
Critical Temperature ◽  
Temperature Dependence ◽  
Kinematic Viscosity ◽  
Arrhenius Equation ◽  
Reaction Rates ◽  
Mechanical Theory ◽  
Statistical Mechanical ◽  
Absolute Reaction

The size of the nanoparticles participating in the viscous flow and the diffusion coefficient were calculated using statistical mechanical theory of absolute reaction rates and the Arrhenius equation. As experimental data, temperature dependence of the kinematic viscosity and density of Fe73.5Cu1Mo3Si13.5B9 melt was used. At a temperature of 1600 K, after the melt is overheated above the critical temperature Tk = 1770 K, the nanoparticles size decreases from 0.92 to 0.47 nm, and the diffusion coefficient increases from 2.4·10-10 to 4.5·10-10 m2·s-1.

scholarly journals Hydrogen tunnelling in enzyme-catalysed H-transfer reactions: flavoprotein and quinoprotein systems

2006 ◽  
Vol 361 (1472) ◽  
pp. 1375-1386 ◽  
Author(s):  
Michael J Sutcliffe ◽  
Laura Masgrau ◽  
Anna Roujeinikova ◽  
Linus O Johannissen ◽  
Parvinder Hothi ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Variable Temperature ◽  
Isotope Effects ◽  
Experimental Studies ◽  
Zero Point ◽  
Reaction Rates ◽  
State Theory ◽  
Strong Temperature Dependence ◽  
Methylamine Dehydrogenase ◽  
Point Energy

It is now widely accepted that enzyme-catalysed C–H bond breakage occurs by quantum mechanical tunnelling. This paradigm shift in the conceptual framework for these reactions away from semi-classical transition state theory (TST, i.e. including zero-point energy, but with no tunnelling correction) has been driven over the recent years by experimental studies of the temperature dependence of kinetic isotope effects (KIEs) for these reactions in a range of enzymes, including the tryptophan tryptophylquinone-dependent enzymes such as methylamine dehydrogenase and aromatic amine dehydrogenase, and the flavoenzymes such as morphinone reductase and pentaerythritol tetranitrate reductase, which produced observations that are also inconsistent with the simple Bell-correction model of tunnelling. However, these data—especially, the strong temperature dependence of reaction rates and the variable temperature dependence of KIEs—are consistent with other tunnelling models (termed full tunnelling models), in which protein and/or substrate fluctuations generate a configuration compatible with tunnelling. These models accommodate substrate/protein (environment) fluctuations required to attain a configuration with degenerate nuclear quantum states and, when necessary, motion required to increase the probability of tunnelling in these states. Furthermore, tunnelling mechanisms in enzymes are supported by atomistic computational studies performed within the framework of modern TST, which incorporates quantum nuclear effects.

scholarly journals The mechanisms and meteorological drivers of the summertime ozone–temperature relationship

2019 ◽  
Vol 19 (21) ◽  
pp. 13367-13381 ◽  
Author(s):  
William C. Porter ◽  
Colette L. Heald
Keyword(s):  
United States ◽  
Temperature Dependence ◽  
Transport Model ◽  
Surface Ozone ◽  
The United States ◽  
Reaction Rates ◽  
Temperature Relationship ◽  
Nox Emissions ◽  
Temperature Dependent ◽  
Temperature Correlation

Abstract. Surface ozone (O3) pollution levels are strongly correlated with daytime surface temperatures, especially in highly polluted regions. This correlation is nonlinear and occurs through a variety of temperature-dependent mechanisms related to O3 precursor emissions, lifetimes, and reaction rates, making the reproduction of temperature sensitivities – and the projection of associated human health risks – a complex problem. Here we explore the summertime O3–temperature relationship in the United States and Europe using the chemical transport model GEOS-Chem. We remove the temperature dependence of several mechanisms most frequently cited as causes of the O3–temperature “climate penalty”, including PAN decomposition, soil NOx emissions, biogenic volatile organic compound (VOC) emissions, and dry deposition. We quantify the contribution of each mechanism to the overall correlation between O3 and temperature both individually and collectively. Through this analysis we find that the thermal decomposition of PAN can explain, on average, 20 % of the overall O3–temperature correlation in the United States. The effect is weaker in Europe, explaining 9 % of the overall O3–temperature relationship. The temperature dependence of biogenic emissions contributes 3 % and 9 % of the total O3–temperature correlation in the United States and Europe on average, while temperature-dependent deposition (6 % and 1 %) and soil NOx emissions (10 % and 7 %) also contribute. Even considered collectively these mechanisms explain less than 46 % of the modeled O3–temperature correlation in the United States and 36 % in Europe. We use commonality analysis to demonstrate that covariance with other meteorological phenomena such as stagnancy and humidity can explain the bulk of the remainder of the O3–temperature correlation. Thus, we demonstrate that the statistical correlation between O3 and temperature alone may greatly overestimate the direct impacts of temperature on O3, with implications for the interpretation of policy-relevant metrics such as climate penalty.

scholarly journals The mechanisms and meteorological drivers of the ozone–temperature relationship

2019 ◽  
Author(s):  
William C. Porter ◽  
Colette L. Heald
Keyword(s):  
United States ◽  
Temperature Dependence ◽  
Transport Model ◽  
Surface Ozone ◽  
The United States ◽  
Reaction Rates ◽  
Temperature Relationship ◽  
Nox Emissions ◽  
Temperature Dependent ◽  
Temperature Correlation

Abstract. Surface ozone (O3) pollution levels are strongly correlated with daytime surface temperatures, especially in highly polluted regions. This correlation is nonlinear and occurs through a variety of temperature dependent mechanisms related to O3 precursor emissions, lifetimes, and reaction rates, making the reproduction of temperature sensitivities – and the projection of associated human health risks – a complex problem. Here we explore the summertime O3–temperature relationship in the United States and Europe using the chemical transport model GEOS-Chem. We remove the temperature dependence of several mechanisms most frequently cited as causes of the O3–temperature climate penalty, including: PAN decomposition, soil NOx emissions, biogenic VOC emissions, and dry deposition. We quantify the contribution of each mechanism to the overall correlation between O3 and temperature both individually and collectively. Through this analysis we find that the thermal decomposition of PAN can explain, on average, 20 % of the overall O3–temperature correlation in the United States. The effect is weaker in Europe, explaining 9 % of the overall O3–temperature relationship. The temperature dependence of biogenic emissions contributes 3 % and 9 % of the total O3–temperature correlation in the United States and Europe on average, while temperature dependent deposition (6 % and 1 %) and soil NOx emissions (10 % and 7 %) also contribute. Even considered collectively these mechanisms explain less than 46 % of the modeled O3–temperature correlation in the United States and 36 % in Europe. We use commonality analysis to demonstrate that covariance with other meteorological phenomena such as stagnancy and humidity can explain the bulk of the remainder of the O3–temperature correlation. Thus, we demonstrate that the statistical correlation between O3 and temperature alone may greatly overestimate the direct impacts of temperature on O3, with implications for the interpretation of policy-relevant metrics such as climate penalty.

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