THERMODYNAMIC PROPERTIES AND GEOCHEMISTRY OF ISOTOPIC COMPOUNDS OF SELENIUM

1962 ◽  
Vol 40 (2) ◽  
pp. 367-375 ◽  
Author(s):  
H. R. Krouse ◽  
H. G. Thode
Keyword(s):  
Partition Function ◽  
Kinetic Isotope Effect ◽  
Chemical Reduction ◽  
Equilibrium Constants ◽  
Elemental Selenium ◽  
Exchange Reactions ◽  
Kinetic Isotope ◽  
Naturally Occurring ◽  
Selenium Isotope ◽  
Selenium Isotopes

Using "normal vibration equations" and statistical mechanics, the isotopic vibrational frequencies and the partition function ratios for various Se76- and Se82-containing compounds have been calculated. The equilibrium constants for selenium isotope exchange reactions derived from these partition function ratios indicate that noticeable fractionation of selenium isotopes can be expected in the laboratory and in naturally occurring processes.The Se82/Se76 ratios for 16 natural samples have been compared mass spectrometrically. Variations of up to 1.5% found in this ratio are discussed.A kinetic isotope effect of 1.5% found in a chemical reduction of selenite ion to elemental selenium is also discussed.

FRACTIONATION OF GERMANIUM ISOTOPES IN CHEMICAL REACTIONS

1964 ◽  
Vol 42 (8) ◽  
pp. 1971-1978 ◽  
Author(s):  
H. M. Brown ◽  
H. R. Krouse
Keyword(s):  
Partition Function ◽  
Isotope Exchange ◽  
Isotope Fractionation ◽  
Kinetic Isotope Effect ◽  
Chemical Reduction ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Kinetic Isotope Effects ◽  
Exchange Reactions ◽  
Kinetic Isotope

Isotopic vibrational frequencies and the corresponding partition-function ratios for several compounds containing Ge70 and Ge76 have been calculated at various temperatures. The theoretical equilibrium constants for germanium isotope-exchange reactions derived from these partition-function ratios indicate that noticeable germanium isotope fractionation might be effected with laboratory reactions. Calculated kinetic isotope effects in the breaking of diatomic bonds also predict observable alterations of the Ge70/Ge76 ratio.A kinetic isotope effect of 1.0% observed in the chemical reduction of GeO2 to GeO is discussed.

Ketonization equilibria of phenol in aqueous solution

1999 ◽  
Vol 77 (5-6) ◽  
pp. 605-613 ◽  
Author(s):  
Marco Capponi ◽  
Ivo G Gut ◽  
Bruno Hellrung ◽  
Gaby Persy ◽  
Jakob Wirz
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Flash Photolysis ◽  
Equilibrium Constants ◽  
Thermodynamic Cycle ◽  
Acidity Constant ◽  
Kinetic Isotope ◽  
Carbon Acids

The two keto tautomers of phenol (1), cyclohexa-2,4-dienone (2) and cyclohexa-2,5-dienone (3), were generated by flash photolysis of appropriate precursors in aqueous solution, and the pH-rate profiles of their enolization reactions, 2 –> 1 and 3 –> 1, were measured. The rates of the reverse reactions, 1 –> 2 and 1 –> 3, were determined from the rates of acid-catalyzed hydron exchange at the ortho- and para-positions of 1; the magnitude of the kinetic isotope effect was assessed by comparing the rates of hydrogenation of phenol-2t and -2d. The ratios of the enolization and ketonization rate constants provide the equilibrium constants of enolization, pKE(2, aq, 25°C) = -12.73 ± 0.12 and pKE(3, aq, 25°C) = -10.98 ± 0.15. Combination with the acidity constant of phenol also defines the acidity constants of 2 and 3 through a thermodynamic cycle. These ketones are remarkably strong carbon acids: pKa(2) = -2.89 ± 0.12 and pKa(3) = -1.14 ± 0.15. They disappear by proton transfer to the solvent with lifetimes, τ(2) = 260 μs and τ(3) = 13 ms, that are insensitive to pH in the range from 3-10.Key words: proton transfer, tautomers, flash photolysis, kinetic isotope effect, pH-rate profiles.

THERMODYNAMIC PROPERTIES OF ISOTOPIC COMPOUNDS OF SULPHUR

1950 ◽  
Vol 28b (9) ◽  
pp. 567-578 ◽  
Author(s):  
A. P. Tudge ◽  
H. G. Thode
Keyword(s):  
Partition Function ◽  
Thermodynamic Properties ◽  
Statistical Mechanics ◽  
Equilibrium Constants ◽  
Sulphur Isotopes ◽  
Exchange Reactions ◽  
Sulphur Compounds ◽  
Exchange Constants

Using the well known methods of statistical mechanics, partition function ratios for many isotopic sulphur compounds have been calculated. These partition function ratios are used to determine equilibrium constants for many possible exchange reactions involving the isotopes of sulphur. The results indicate that considerable fractionation of the sulphur isotopes can be expected in laboratory and natural occurring processes. The predicted exchange constants are discussed in the light of recent results on the distribution of the sulphur isotopes in nature.

Sulfur isotope effects in volcanic gas mixtures

1970 ◽  
Vol 7 (6) ◽  
pp. 1402-1409 ◽  
Author(s):  
V. A. Grinenko ◽  
H. G. Thode
Keyword(s):  
Isotope Exchange ◽  
Sulfur Isotope ◽  
Chemical Reduction ◽  
Isotope Effects ◽  
Exchange Constant ◽  
Exchange Reactions ◽  
Volcanic Gas ◽  
Temperature Changes ◽  
Kinetic Isotope ◽  
Exchange Constants

Sulfur isotope effects in the exchange systems (1) [Formula: see text] and (2) [Formula: see text] have been studied at various temperatures. It has been shown that in the presence of water vapor sulfur isotope exchange proceeds at an appreciable rate in (1) above 150 °C and in (2) above 300 °C.The isotopic exchange constant for (1) approaches unity in the temperature range from 200 to 400 °C and the exchange constants for (2) at 400 °C and 450 °C equal 1.0095 and 1.0090 respectively favoring 34S in the SO2.The kinetic isotope effect in the chemical reduction of SO2 to S0 in consequence of its interaction with H2S has been determined at 25 °C, 200 °C, and 280 °C. At these temperatures the 32SO2 molecules react 1.6% faster than the 34SO2 molecules.It is concluded that the spread in isotopic composition of various forms of sulfur in volcanic gases is caused not only by isotope exchange reactions between oxidized and reduced forms of sulfur but also by kinetic isotope effects in unidirectional reactions which result from major temperature changes at the outflow.

scholarly journals Strong inverse kinetic isotope effect observed in ammonia charge exchange reactions

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
L. S. Petralia ◽  
A. Tsikritea ◽  
J. Loreau ◽  
T. P. Softley ◽  
B. R. Heazlewood
Keyword(s):  
Isotope Effect ◽  
Potential Energy Surfaces ◽  
Kinetic Isotope Effect ◽  
Valuable Insight ◽  
Isotopic Substitution ◽  
Exchange Reactions ◽  
Kinetic Isotope ◽  
Reaction Complex ◽  
Energy Surfaces ◽  
Insight Into

AbstractIsotopic substitution has long been used to understand the detailed mechanisms of chemical reactions; normally the substitution of hydrogen by deuterium leads to a slower reaction. Here, we report our findings on the charge transfer collisions of cold $${{\rm{Xe}}}^{+}$$Xe+ ions and two isotopologues of ammonia, $${{\rm{NH}}}_{3}$$NH3 and $${{\rm{ND}}}_{3}$$ND3. Deuterated ammonia is found to react more than three times faster than hydrogenated ammonia. Classical capture models are unable to account for this pronounced inverse kinetic isotope effect. Moreover, detailed ab initio calculations cannot identify any (energetically accessible) crossing points between the reactant and product potential energy surfaces, indicating that electron transfer is likely to be slow. The higher reactivity of $${{\rm{ND}}}_{3}$$ND3 is attributed to the greater density of states (and therefore lifetime) of the deuterated reaction complex compared to the hydrogenated system. Our observations could provide valuable insight into possible mechanisms contributing to deuterium fractionation in the interstellar medium.

scholarly journals Isotopic Partition Function Ratios Involving H2, H2O, H2S, H2Se, and NH3

1973 ◽  
Vol 28 (2) ◽  
pp. 129-136 ◽  
Author(s):  
J. Bron ◽  
Chen Fee Chang ◽  
M. Wolfsberg
Keyword(s):  
Partition Function ◽  
Least Squares ◽  
Gas Phase ◽  
Isotopic Exchange ◽  
Equilibrium Constants ◽  
Heavy Atom ◽  
Harmonic Approximation ◽  
Ideal Gas ◽  
Correction Factors ◽  
Exchange Reactions

Ideal gas phase isotopic partition function ratios involving both deuterium and tritium substitution for hydrogen and also heavy atom substitution in H2, H2O, H2S, H2Se, and NH3 have been calculated at a number of temperatures. The results have been least squares fitted to a five term series in powers of (300/T). Various correction factors to the harmonic approximation were considered in the calculation of the partition function ratios. It is demonstrated that the tabulated ratios can be used to calculate equilibrium constants for isotopic exchange reactions.

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