Hydrogen isotope fractionation in the photolysis of formaldehyde

Abstract. Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in H2 produced is 500(±20)‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotopic ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O + hν → CHO + H) as compared to the molecular channel (CH2O + hν → H2 + CO) of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotopic ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2 (αm) but also by overall fractionation for the removal processes of CH2O (αf), and is represented by the ratio of αm/αf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αm/αf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αm/αf can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH4) by the factor of 1.2–1.3 as anticipated in the literature.

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Hydrogen isotope fractionation in the photolysis of formaldehyde

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-1353-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 1353-1366 ◽

Cited By ~ 22

Author(s):

T. S. Rhee ◽

C. A. M. Brenninkmeijer ◽

T. Röckmann

Keyword(s):

Isotope Ratio ◽

Isotope Fractionation ◽

Isotopic Fractionation ◽

Photochemical Oxidation ◽

Atmospheric Conditions ◽

Isotopic Enrichment ◽

Fractionation Factor ◽

Removal Processes ◽

Molecular Channel ◽

Fractionation Factors

Abstract. Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in the H2 produced is 500(±20)‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotope ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O+hν → CHO+H) as compared to the molecular channel (CH2O+hν → H2+CO) of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotope ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2 (αm) but also by overall fractionation for the removal processes of CH2O (αf), and is represented by the ratio of αm/αf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αm/αf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αm/αf can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH4) by the factor of 1.2–1.3 as anticipated in the literature.

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Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Minerals ◽

10.3390/min11020208 ◽

2021 ◽

Vol 11 (2) ◽

pp. 208

Author(s):

Takuma Hasegawa ◽

Kotaro Nakata ◽

Rhys Gwynne

Keyword(s):

Groundwater Flow ◽

Diffusion Coefficients ◽

Isotope Fractionation ◽

Free Water ◽

Effective Porosity ◽

Diffusion Experiment ◽

Fractionation Factor ◽

Through Diffusion ◽

Geological Formations ◽

Fractionation Factors

For radioactive waste disposal, it is important that local groundwater flow is slow as groundwater flow is the main transport medium for radioactive nuclides in geological formations. When the groundwater flow is very slow, diffusion is the dominant transport mechanism (diffusion-dominant domain). Key pieces of evidence indicating a diffusion-dominant domain are the separation of components and the fractionation of isotopes by diffusion. To prove this, it is necessary to investigate the different diffusion coefficients for each component and the related stable isotope fractionation factors. Thus, in this study, through-diffusion and effective-porosity experiments were conducted on selected artificial materials and natural rocks. We also undertook measurements relating to the isotope fractionation factors of Cl and Br isotopes for natural samples. For natural rock samples, the diffusion coefficients of water isotopes (HDO and H218O) were three to four times higher than those of monovalent anions (Cl−, Br- and NO3−), and the isotope fractionation factor of 37Cl (1.0017–1.0021) was slightly higher than that of free water. It was experimentally confirmed that the isotope fractionation factor of 81Br was approximately 1.0007–1.0010, which is equivalent to that of free water. The enrichment factor of 81Br was almost half that of 37Cl. The effective porosity ratios of HDO and Cl were slightly different, but the difference was not significant compared to the ratio of their diffusion coefficients. As a result, component separation was dominated by diffusion. For artificial samples, the diffusion coefficients and effective porosities of HDO and Cl were almost the same; it was thus difficult to assess the component separation by diffusion. However, isotope fractionation of Cl and Br was confirmed using a through-diffusion experiment. The results show that HDO and Cl separation and isotope fractionation of Cl and Br can be expected in diffusion-dominant domains in geological formations.

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Bromine Isotope Variations in Magmatic and Hydrothermal Sodalite and Tugtupite and the Estimation of Br Isotope Fractionation between Melt and Sodalite

Minerals ◽

10.3390/min11040370 ◽

2021 ◽

Vol 11 (4) ◽

pp. 370

Author(s):

Hans G. M. Eggenkamp ◽

Michael A. W. Marks ◽

Pascale Louvat ◽

Gregor Markl

Keyword(s):

Late Stage ◽

Isotope Fractionation ◽

Isotope Composition ◽

Fractionation Factor ◽

Data Set ◽

Geothermal Fluids ◽

A Value ◽

Isotope Fractionation Factor ◽

Very High ◽

Fractionation Factors

We determined the bromine isotope compositions of magmatic and hydrothermal sodalite (Na8Al6Si6O24Cl2) and tugtupite (Na8Al2Be2Si8O24Cl2) from the Ilímaussaq intrusion in South Greenland, in order to constrain the Br isotope composition of the melt and hydrothermal fluids from which these minerals were formed. Early formed magmatic sodalite has high Br contents (138 ± 10 µg/g, n = 5) and low δ81Br values (+0.23 ± 0.07‰). Late stage hydrothermal sodalite has lower Br contents (53±10 µg/g, n = 5) and higher δ81Br values (+0.36 ± 0.08‰). Tugtupite that forms at even later stages shows the lowest Br contents (26 ± 2 µg/g, n = 2) and the highest δ81Br values (+0.71 ± 0.17‰). One hydrothermal sodalite has a Br concentration of 48 ± 9 µg/g and an exceptionally high δ81Br of 0.82 ± 0.12‰, very similar to the δ81Br of tugtupites. We suggest that this may be a very late stage sodalite that possibly formed under Be deficient conditions. The data set suggests that sodalite crystallises with a negative Br isotope fractionation factor, which means that the sodalite has a more negative δ81Br than the melt, of −0.3 to −0.4‰ from the melt. This leads to a value of +0.5 to +0.6‰ relative to SMOB for the melt from which sodalite crystallises. This value is similar to a recently published δ81Br value of +0.7‰ for very deep geothermal fluids with very high R/Ra He isotope ratios, presumably derived from the mantle. During crystallisation of later stage hydrothermal sodalite and the Be mineral tugtupite, δ81Br of the residual fluids (both melt and hydrothermal fluid) increases as light 79Br crystallises in the sodalite and tugtupite. This results in increasing δ81Br values of later stage minerals that crystallise with comparable fractionation factors from a fluid with increasingly higher δ81Br values.

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Boron isotope fractionation during brucite deposition from artificial seawater

Climate of the Past ◽

10.5194/cp-7-693-2011 ◽

2011 ◽

Vol 7 (3) ◽

pp. 693-706 ◽

Cited By ~ 6

Author(s):

J. Xiao ◽

Y. K. Xiao ◽

C. Q. Liu ◽

Z. D. Jin

Keyword(s):

Isotope Fractionation ◽

Boron Concentration ◽

Isotopic Fractionation ◽

Artificial Seawater ◽

Simultaneous Occurrence ◽

Precipitation Reaction ◽

Ph Values ◽

The Relationship ◽

Preferential Incorporation ◽

Fractionation Factors

Abstract. Experiments involving boron incorporation into brucite (Mg(OH)2) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite and the influence of it on Mg/Ca-SST proxy and δ11B-pH proxy. The results show that both the concentration of boron in deposited brucite ([B]d) and its boron partition coefficient (Kd) between deposited brucite and final seawater are controlled by the pH of the solution. The incorporation capacity of boron into brucite is almost the same as that into corals, but much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (δ11Bd) are higher than those in the associated artificial seawater (δ11Bisw) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)3 into brucite. Both boron adsorptions onto brucite and the precipitation reaction of H3BO3 with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into corals. The existence of brucite in corals can affect the δ11B and Mg/Ca in corals and influences the Mg/Ca-SST proxy and δ11B-pH proxy negatively. The relationship between δ11B and Mg/Ca in corals can be used to judge the existence of brucite in corals, which should provide a reliable method for better use of δ11B and Mg/Ca in corals to reconstruct paleo-marine environment.

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Solvent and substrate isotope effects on the enolization and carbon-acid ionization of isobutyrophenone

Canadian Journal of Chemistry ◽

10.1139/v96-278 ◽

1996 ◽

Vol 74 (12) ◽

pp. 2481-2486 ◽

Cited By ~ 3

Author(s):

J.R. Keeffe ◽

A.J. Kresge

Keyword(s):

Isotope Effect ◽

Isotope Effects ◽

Isotopic Fractionation ◽

Medium Effect ◽

Solvent Isotope Effect ◽

Fractionation Factor ◽

Solvent Isotope ◽

Carbon Acid ◽

Fractionation Factors ◽

Acid Ionization

Bromine scavenging was used to measure rates of acid-catalyzed enolization of isobutyrophenone in H2O and in D2O solution and of isobutyrophenone-α-d in D2O solution. The results provide the solvent isotope effect kH +/kD + = 0.56 and the substrate isotope effect kH/kD = 6.2 on the enolization reaction, both of which are consistent with the generally accepted mechanism for this process. The present results in combination with literature information also provide the solvent isotope effect on the enolization equilibrium, KE(H2O)/KE(D2O) = 0.92, and the solvent isotope effect on the ionization of isobutyrophenone as a carbon acid, kaK(H2O)/kaK(D2O) = 5.4, as well as the product of isotopic fractionation factor and medium effect, [Formula: see text], for isobutyrophenone enol and the medium effect, Φ = 0.47, for its enolate ion. The isotope effect on KE is the first ever determined for the keto–enol equilibrium of a simple aldehyde or ketone; its near-unit value is consistent with expectation on the basis of fractionation factors for the species involved. Key words: isobutyrophenone, keto–enol equilibrium, carbon-acid ionization, solvent isotope effects, isotopic fractionation factors.

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Hydrogen isotope fractionation between methanol and diphenylphosphine or dimethylphosphine in the gas phase and in aprotic solvents

Canadian Journal of Chemistry ◽

10.1139/v96-163 ◽

1996 ◽

Vol 74 (8) ◽

pp. 1465-1469

Author(s):

Andrzej Wawer ◽

Jerzy Szydtlowski

Keyword(s):

Interaction Energy ◽

Gas Phase ◽

Hydrogen Isotope ◽

Isotope Fractionation ◽

Isotope Effects ◽

Solvent Polarity ◽

Exchange Reactions ◽

Fractionation Factor ◽

The Given ◽

Fractionation Factors

D/H fractionation factors between MeOH and Ph2PH in dilute solutions of tetrachloroethylene, benzene, tetrahydrofuran, pyridine, and acetonitrile and T/H fractionation factors between MeOH and Me2PH vapors were measured. The experimental results agree very well with values calculated from the statistical theory of isotope effects formulated by Bigeleisen and Mayer. There are correlations between observed fractionation factors and solvent polarity, and the interaction energy of methanol with the given solvent. Another correlation has been found between enthalpy of the exchange reactions and the interaction energy between methanol and the given solvent. Key words: isotope effects, fractionation factor, diphenylphosphine, methanol.

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Influence of climate change on carbon and oxygen isotope fractionation factors between glucose and α-cellulose of pine wood

Geochronometria ◽

10.2478/s13386-013-0104-y ◽

2013 ◽

Vol 40 (2) ◽

pp. 145-152 ◽

Cited By ~ 11

Author(s):

Barbara Sensuła ◽

Anna Pazdur

Keyword(s):

Climate Change ◽

Oxygen Isotope ◽

Isotope Fractionation ◽

Mean Value ◽

Fractionation Factor ◽

Oxygen Isotope Fractionation ◽

Climate Signal ◽

Carbon And Oxygen Isotope ◽

The Relationship ◽

Fractionation Factors

Abstract We present the first analysis of the influence of climate change on carbon and oxygen isotope fractionation factors for two saccharides (glucose and α-cellulose) of pine wood. The conifers grew in the Niepołomice Forest in Poland and the annual rings covered a time span from 1935 to 2000 AD. Glucose samples from acid hydrolysis of α-cellulose were extracted from annual tree rings. The carbon and oxygen isotope fractionation factors between glucose and α-cellulose were not stable over time. The mean value for the carbon isotope fractionation factors between glucose and α-cellulose was greater than unity. The mean value for the oxygen isotope fractionation factors between glucose and α-cellulose was lower than unity. We established, with respect to climate change, the significance of the interannual and intraannual variation in the carbon and oxygen isotope fractionation factors between both saccharides. We used moving interval correlation results for May of the previous year through September of the current year using a base length of 48 years. The relationship with summer temperature is the main climate signal in the carbon isotope fractionation factor between glucose and α-cellulose. The relationship with autumn sunshine is the main climate signal in the oxygen isotope fractionation factor between glucose and α-cellulose for the tree ring chronology.

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Experiments on Cu-isotope fractionation between chlorine-bearing fluid and silicate magma: implications for fluid exsolution and porphyry Cu deposits

National Science Review ◽

10.1093/nsr/nwz221 ◽

2020 ◽

Vol 7 (8) ◽

pp. 1319-1330

Author(s):

Haihao Guo ◽

Ying Xia ◽

Ruixia Bai ◽

Xingchao Zhang ◽

Fang Huang

Keyword(s):

Inductively Coupled Plasma ◽

Hydrothermal Fluid ◽

Isotope Fractionation ◽

Aqueous Fluid ◽

Pressure Vessels ◽

Experimental Results ◽

Fractionation Factor ◽

Cu Isotopes ◽

Fractionation Factors ◽

Cu Isotope

Abstract Hydrothermal fluid is essential for transporting metals in the crust and mantle. To explore the potential of Cu isotopes as a tracer of hydrothermal-fluid activity, Cu-isotope fractionation factors between Cl-bearing aqueous fluids and silicate magmas (andesite, dacite, rhyolite dacite, rhyolite and haplogranite) were experimentally calibrated. Fluids containing 1.75–14 wt.% Cl were mixed together with rock powders in Au95Cu5 alloy capsules, which were equilibrated in cold-seal pressure vessels for 5–13 days at 800–850°C and 2 kbar. The elemental and Cu-isotopic compositions of the recovered aqueous fluid and solid phases were analyzed by (LA-) ICP–MS and multi-collector inductively coupled plasma mass spectrometry, respectively. Our experimental results show that the fluid phases are consistently enriched in heavy Cu isotope (65Cu) relative to the coexisting silicates. The Cu-isotope fractionation factor (Δ65CuFLUID-MELT) ranges from 0.08 ± 0.01‰ to 0.69 ± 0.02‰. The experimental results show that the Cu-isotopic fractionation factors between aqueous fluids and silicates strongly depend on the Cu speciation in the fluids (e.g. CuCl(H2O), CuCl2– and CuCl32−) and silicate melts (CuO1/2), suggesting that the exsolved fluids may have higher δ65Cu than the residual magmas. Our results suggest the elevated δ65Cu values in Cu-enriched rocks could be produced by addition of aqueous fluids exsolved from magmas. Together with previous studies on Cu isotopes in the brine and vapor phases of porphyry deposits, our results are helpful for better understanding Cu-mineralization processes.

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The role of marine sediment diagenesis in the modern oceanic magnesium cycle

Nature Communications ◽

10.1038/s41467-019-12322-2 ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 5

Author(s):

Richard D. Berg ◽

Evan A. Solomon ◽

Fang-Zhen Teng

Keyword(s):

Isotopic Ratio ◽

Isotopic Fractionation ◽

Mineral Formation ◽

Fractionation Factor ◽

Sources And Sinks ◽

Sediment Diagenesis ◽

Authigenic Mineral ◽

Ridge Flank

Abstract The oceanic magnesium cycle is largely controlled by continental weathering and marine authigenic mineral formation, which are intimately linked to long-term climate. Uncertainties in the magnesium cycle propagate into other chemical budgets, and into interpretations of paleo-oceanographic reconstructions of seawater δ26Mg and Mg/Ca ratios. Here, we produce a detailed global map of the flux of dissolved magnesium from the ocean into deeper marine sediments (greater than ∼1 meter below seafloor), and quantify the global flux and associated isotopic fractionation. We find that this flux accounts for 15–20% of the output of magnesium from the ocean, with a flux-weighted fractionation factor of ∼0.9994 acting to increase the magnesium isotopic ratio in the ocean. Our analysis provides the best constraints to date on the sources and sinks that define the oceanic magnesium cycle, including new constraints on the output flux of magnesium and isotopic fractionation during low-temperature ridge flank hydrothermal circulation.

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Theoretical analyses of chemical and magnesium and silica isotope fractionation during vaporization of ca-al-inclusion of chondrite

Геохимия ◽

10.31857/s0016-7525648777-793 ◽

2019 ◽

Vol 64 (8) ◽

pp. 777-793

Author(s):

O. I. Yakovlev ◽

S. I. Shornikov

Keyword(s):

Isotope Fractionation ◽

Isotopic Fractionation ◽

Theoretical Description ◽

Rayleigh Equation ◽

Fractionation Factor ◽

Silicon Isotopes ◽

Alternative Expression ◽

Close Relationship ◽

Rate Of Evaporation ◽

Relationship Of

Experimental study of changes in the composition of Ca-Al-inclusions of chondrites during evaporation indicates a close relationship of chemical and isotopic fractionation of this substance. The theoretical description of the coupling is carried out using the equations of the evaporation rate of the melt component (the Hertz-Knudsen equation) and isotope Rayleigh fractionation. The form of Rayleigh equation taken in foreign literature, derived from the Hertz-Knudsen equation, faces difficulties in interpreting experimental data. The discrepancy between the experimental and model data is explained by the fact that the «ideal» isotope fractionation factor used in the Rayleigh equation does not take into account its dependence on the temperature and composition of the evaporating melt. The article presents an alternative expression of the Rayleigh equation and a new expression of the rate of evaporation of Hertz-Knudsen, taking into account the activity of the melt component. The activity of the component is determined by the acidity-basicity index of the melt Ca-Al-inclusion, which, in turn, affects the evaporative fractionation of magnesium and silicon isotopes.

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