Isotopic Coefficient Research Articles

The generation mechanism of deep natural gas in Tabei uplift, Tarim Basin, Northwest China: insights from instantaneous and accumulative effects

The natural gas heavy carbon isotope and high dryness coefficients genesis in Tabei uplift, Tarim Basin has been highly controversial. To investigate the generation mechanisms of natural gas in the Tabei Uplift. Natural gas chemical composition, carbon isotopes were used to analyze the genesis of natural gas, source rock maturity, and basin modeling were conducted to reconstruct the natural gas generation process, and the influences of instantaneous and cumulative effects on natural gas properties was discussed. The results show that the dryness coefficients of natural gas range from 0.62 to 0.99 (average: 0.92), the methane contents range from 30.42% to 96.4% (average: 85.10%), ethane contents from 0.43% to 15.58% (average: 3.39%), propane contents from 0.11% to 11.43% (average: 1.78%), and the methane carbon isotopes range from −47.30‰ to −33.80‰ (average: −36.96‰), ethane carbon isotopes range from −39.60‰ to −33.20‰ (average: −35.57‰), propane carbon isotopes range from −36.90‰ to −28.50‰ (average: −35.49‰). Compared with the actual regional thermal evolution of the source rock (Ro% range from 1.4%∼1.7%), the natural gas exhibits excessively high dryness coefficients and heavy methane carbon isotope characteristics. The natural gas is primary cracking gas and sourced from marine type II kerogen. The dryness coefficient, methane carbon isotopes, and source rock maturity gradually increases from the west to the east. Instantaneous effects and leakage led to the dry gas and relative heavy methane carbon isotopes generated at a low maturity level. The current natural gas in the Ordovician reservoirs was all generated during the Himalayan orogeny. Long period pause of the gas generation between the two hydrocarbon generation phases is the main cause for the instantaneous effects.

The evolution of dissolved inorganic carbon (DIC) and δ13CDIC in acid mine drainage polluted karst rivers: Preliminary findings from laboratory experiments

Acid mine drainage (AMD) has caused serious pollution in the surface water environments of karst areas, but the effect of AMD on the dissolved inorganic carbon (DIC) dynamics in the receiving karst rivers remains poorly understood. The AMD and karst river water were sampled from the Yangliujie River watershed in Southwest China, and mixed different proportions of AMD and karst river water in a laboratory experiment to simulate seasonal hydrological conditions in the river, in an attempt to explore the impact of AMD on the loss rate and evolution of DIC in karst river water. The results showed that AMD can cause a rapid pH drop in karst river water, resulting in approximately 41.0 ± 11.8 % DIC loss in the early stage of mixing as CO2(g) release to the atmosphere. With the biological or chemical oxidation of Fe2+, and followed by Fe3+ biogenic formation of schwertmannite or hydrolysis, the pH decreased and the DIC concentration further decreased in the mixed samples, the degree of decrease was related to the oxidation rate of Fe2+. With decreasing DIC concentration, δ13CDIC enrichment gradually increased. When the mixing ratio of AMD was large, the total H+ in AMD and H+ generated by the oxidation of Fe2+ exceeded the HCO3− content in karst river water, the isotopic enrichment coefficient caused by the initial mixing and the end of the reaction was small, and the DIC transformation was mainly dominated by the loss of CO2(g). When a small proportion of AMD was mixed in, the HCO3− concentration in the mixed water sample was in excess of the H+ produced by Fe2+ and the total H+ in AMD, the isotopic enrichment coefficient caused by the initial mixing and the end of the reaction was larger, and the DIC conversion was mainly affected by HCO3− dehydration. These preliminary findings support evidence showing DIC conversion and loss in AMD-affected karst rivers increase the transfer of carbon dioxide to the atmosphere, which diminishes net carbon sink fluxes in karst river basins, so reasonable AMD treatment methods should be applied to minimize these negative impacts.

Improved volume variable cluster model method for crystal-lattice optimization: effect on isotope fractionation factor

The isotopic fractionation factor and element partition coefficient can be calculated only after the geometric optimization of the molecular clusters is completed. Optimization directly affects the accuracy of some parameters, such as the average bond length, molecular volume, harmonic vibrational frequency, and other thermodynamic parameters. Here, we used the improved volume variable cluster model (VVCM) method to optimize the molecular clusters of a typical oxide, quartz. We documented the average bond length and relative volume change. Finally, we extracted the harmonic vibrational frequencies and calculated the equilibrium fractionation factor of the silicon and oxygen isotopes. Given its performance in geometrical optimization and isotope fractionation factor calculation, we further applied the improved VVCM method to calculate isotope equilibrium fractionation factors of Cd and Zn between the hydroxide (Zn–Al layered double hydroxide), carbonate (cadmium-containing calcite) and their aqueous solutions under superficial conditions. We summarized a detailed procedure and used it to re-evaluate published theoretical results for cadmium-containing hydroxyapatite, emphasizing the relative volume change for all clusters and confirming the optimal point charge arrangement (PCA). The results showed that the average bond length and isotope fractionation factor are consistent with those published in previous studies, and the relative volume changes are considerably lower than the results calculated using the periodic boundary method. Specifically, the average Si–O bond length of quartz was 1.63 Å, and the relative volume change of quartz centered on silicon atoms was − 0.39%. The average Zn–O bond length in the Zn–Al-layered double hydroxide was 2.10 Å, with a relative volume change of 1.96%. Cadmium-containing calcite had an average Cd–O bond length of 2.28 Å, with a relative volume change of 0.45%. At 298 K, the equilibrium fractionation factors between quartz, Zn–Al-layered double hydroxide, cadmium-containing calcite, and their corresponding aqueous solutions were Delta ^{30/28} {text{Si}}_{{{text{Qtz-H}}_{4} {text{SiO}}_{4} }} = 2.20{permil} , Delta^{18/16} {text{O}}_{ {text{Qtz}}{-} ( {text{H}}_{2} {text{O}} )_{text{n}}} = 36.05{permil}, Delta^{66/64} {text{Zn}}_{ {text{Zn}} {-} {text{Al LDH-Zn}} ( {text{H}}_{2} {text{O}} )_{text{n}}^{2+}} = 1.12{permil} and Delta^{114/110} {text{Cd}}_{ {text{(Cd--Cal)-Cd}} ( {text{H}}_{2} {text{O}} )_ {text{n}}^{2 +} } = - 0.26{permil} respectively. These results strongly support the reliability of the improved VVCM method for geometric optimization of molecular clusters.

Determination of the stable carbon isotopic compositions of 2-methyltetrols for four forest areas in Southwest China: The implications for the δ13C values of atmospheric isoprene and C3/C4 vegetation distribution

Isoprene is the most abundant non-methane hydrocarbons (NMHCs) in the troposphere and is released predominantly by vegetation. The δ13C values of atmospheric isoprene vary with different plant types (e.g. C3 and C4 plants). In this work, aerosol samples were collected in four forest areas in Sichuan Province, China, i.e., the Baima Spring Scenic Area (BM), the Panzhihua Cycas Nature Reserve (PZ), the Gongga Mountain National Nature Reserve (GG) and the Wolong National Nature Reserve (WL) during the summers of 2010–2012. The stable carbon isotopic compositions of 2-methyltetrols, the stable products of isoprene oxidation by OH, were measured using a GC/C/IRMS (gas chromatography/combustion/isotopic ratio mass spectrometry) with methylboronic acid derivatization. The stable carbon isotopic fractionation coefficient of isoprene oxidized by OH (OHεi) was derived in laboratory. With the δ13C values of 2-methyltetrols, OHεi and meteorological parameters, the δ13C values of atmospheric isoprene were calculated. The results show that forests can remarkably change the δ13C values of isoprene in the regional scales, making significant contributions to isoprene emissions. Moreover, C3/C4 proportions of shrubs and grasses depend on altitudes. The average δ13C values of atmospheric isoprene are −24.18 ± 1.72‰, −25.81 ± 1.36‰, −24.96 ± 0.94‰, −25.89 ± 1.35‰ for BM, PZ, GG and WL, respectively. The average δ13C value of atmospheric isoprene in SW China and the surrounding areas was −25.23 ± 1.44‰. C4 plants emitted 26.9 ± 10.3% of isoprene in the research atmosphere.

Variation of Isotope Coefficient with Number of CuO2 Layers in High TC Superconductors

In this paper, an effort has been made to study the isotope coefficient in high TC Superconductors by using the variation of isotopic coefficient with the number of CuO2 layers and the variation of isotope coefficients on transition temperature TC . The Hamiltonian for CuO2 layers using BCS type model and extra term of interlayer interaction between CuO2 layers has been considered. Expressions for isotope effect (α) and transition temperature (TC) are obtained and numerically calculated for experimental values by using Green’s function technique.

Use of glucose and carbon isotope fractionation by microbial cells immobilized on solid-phase surface

By the example of glucose uptake by the soil bacteria Pseudomonas aureofaciens BS1393(pBS216) and Rhodococcus sp. 3–30 immobilized on a solid-phase surface (quartz sand), their growth parameters were determined: growth rate (doubling time), total CO2 production, CO2 production per cell, lag period with respect to substrate uptake, respiratory quotient. The growth of P. aureofaciens and Rhodococcus sp. on glucose revealed (1) differences of the lag period with respect to substrate (lag time of ∼4 h for P. aureofaciens and ∼26 h for Rhodococcus sp.); (2) differences between the maximal rates of CO2 production (∼50 μg C-CO2 g−1 sand h−1 for P. aureofaciens and ∼8.5 μg C-CO2 g−1 sand h−1 for Rhodococcus sp.); (3) differences in CO2 production per cell (∼1.94 × 10−9 μM CO2/CFU for P. aureofaciens and more than ∼3.4 × 10−9 μM CO2/CFU for Rhodococcus sp.). The kinetics of the metabolic CO2 isotopic composition was shown to be determined by the difference in the carbon isotopic characteristics of products in the cell. Upon introduction of glucose into the medium (the preparatory stage of the metabolism), the uptake of intracellular 13C-depleted products (lipids) is noted; at the stage of the maximal cell growth rate, introduced glucose is mainly metabolized; and at the final stage, upon exhaustion of substrate, the “stored” products—the lipid fraction—get involved in the metabolism. At the maximal rate of glucose uptake, the CO2 carbon isotopic fractionation coefficient relative to organic products of microbial biosynthesis was determined to be α = 1.009 ± 0.002.

Inverse Iron Isotope Effect in FeSe0.35Te0.65

Abstract We study an iron isotope effect of FeSe1- x Te x ( x =0.65) polycrystalline samples with three types of iron isotopes (54Fe, natural Fe, and 57Fe) which were synthesized carefully in order to rule out differences in the Te content x between them. Our estimate of an isotope coefficient αFe defined by –d ln T c/ d ln M , where T c and M are the superconducting transition temperature and the iron isotope mass, is -0.54(1). Measurements of powder x-ray diffraction (XRD) show no significant difference in lattice parameters between the samples. These indicate that compositionally well-controlled FeSe1- x Te x may possess inverse iron isotope coefficients.

Multiple-sulfur isotope effects during photolysis of carbonyl sulfide

Abstract. Laboratory experiments were carried out to determine sulfur isotope effects during ultraviolet photolysis of carbonyl sulfide (OCS) to carbon monoxide (CO) and elemental sulfur (S0). The OCS gas at 3.7 to 501 mbar was irradiated with or without a N2 bath gas using a 150 W Xe arc lamp. Sulfur isotope ratios for the product S0 and residual OCS were analyzed by an isotope ratio mass-spectrometer with SF6 as the analyte gas. The isotope fractionation after correction for the reservoir effects is −6.8‰ for the ratio 34S/32S, where product S0 is depleted in heavy isotopes. The magnitude of the overall isotope effect is not sensitive to the addition of N2 but increases to −9.5‰ when radiation of λ > 285 nm is used. The measured isotope effect reflects that of photolysis as well as the subsequent sulfur abstraction (from OCS) reaction. The magnitude of isotope effects for the abstraction reaction is estimated by transition state theory to be between −18.9 and −3.1‰ for 34S which gives the photolysis isotope effect as −10.5 to +5.3‰. The observed triple isotope coefficients are ln(δ34S + 1)/ln(δ34S + 1) = 0.534 ± 0.005 and ln(δ36S + 1)/ln(δ34S + 1) = 1.980 ± 0.021. These values differ from canonical values for mass-dependent fractionation of 0.515 and 1.90, respectively. The result demonstrates that the OCS photolysis does not produce large isotope effects of more than about 10‰ for 34S/32S, and can be the major source of background stratospheric sulfate aerosol (SSA) during volcanic quiescence.

Large isotope effect onTcin cuprates despite a small electron-phonon coupling

We calculate the isotope coefficients $\ensuremath{\alpha}$ and ${\ensuremath{\alpha}}^{\ensuremath{\ast}}$ for the superconducting critical temperature ${T}_{c}$ and the pseudogap temperature ${T}^{\ensuremath{\ast}}$ in a mean-field treatment of the $t\text{\ensuremath{-}}J$ model including phonons. The pseudogap phase is identified with the $d$-charge-density wave $(d\text{-CDW})$ phase in this model. Using the small electron-phonon coupling constant ${\ensuremath{\lambda}}_{d}\ensuremath{\sim}0.02$ obtained previously in local-density approximation calculations in ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7}$, ${\ensuremath{\alpha}}^{\ensuremath{\ast}}$ is negative but negligibly small, whereas $\ensuremath{\alpha}$ increases from about 0.03 at optimal doping to values around 1 at small dopings, in agreement with the general trend observed in many cuprates. Using a simple phase fluctuation model where the $d\text{-CDW}$ has only short-range correlations, it is shown that the large increase of $\ensuremath{\alpha}$ at low dopings is rather universal and does not depend on the existence of sharp peaks in the density of states in the pseudogap state or on specific values of the phonon cutoff. Rather, it is caused by the large depletion of spectral weight at low frequencies by the $d\text{-CDW}$ and thus should also occur in other realizations of the pseudogap.

Isotopic Distribution Coefficient of Tritiated Water Adsorbed on Faujasite-Type Zeolite

The fixed-bed adsorption processusing zeolite has been studied as one of the promising processes for the recovery of tritiated water in the field of nuclear fusion. In H2O-HTO binary systems, the difference in adsorption rate must be considered to obtain the isotopic distribution coefficient of tritiated water adsorbed on zeolite. The static method is probably the best approach to measure the distribution coefficient considering the difference in adsorption rate. In this study, the influence of framework SiO2/Al2O3 ratio ranging from 2.0 to 10.0 and of cations (K+, Na+, Ca2+) on isotopic distribution coefficient of tritiated water adsorbed on faujasite-type zeolite was systematically examined. The isotopic distribution coefficient of tritiated water between water adsorbed on zeolite absorbent was 1.1˜1.4. The effect of framework SiO2 to Al2O3 ratio of the X/Y type zeolite on the isotopic distribution coefficient depended on the content of cation in zeolite. The framework SiO2 to Al2O3 ratio of the NaX/NaY zeolite had negligible effect on the isotopic distribution coefficient. The considerable effect of framework SiO2 to Al2O3 ratio was found in the case of KX/KY and CaX/CaY zeolite.

Isotopic Distribution Coefficient of Tritiated Water Adsorbed on Faujasite-Type Zeolite

Isotopic Distribution Coefficient of Tritiated Water Adsorbed on Faujasite-Type Zeolite

High-TcSuperconductivity in Superhard DiamondlikeBC5

Using density functional theory calculations we show that the recently synthesized superhard diamondlike BC5 is superconducting with a critical temperature of the same order as that of MgB2. The average electron-phonon coupling is lambda=0.89, the phonon-frequency logarithmic average is <omega>log=67.4 meV, and the isotope coefficients are alpha(C)=0.3 and alpha(B)=0.2. In BC5, superconductivity is mostly sustained by concerted vibrations of the B atom and its C neighbors.

Estimating the Triple-Point Isotope Effect and the Corresponding Uncertainties for Cryogenic Fixed Points

The sensitivities of melting temperatures to isotopic variations in monatomic and diatomic atmospheric gases using both theoretical and semi-empirical methods are estimated. The current state of knowledge of the vapor-pressure isotope effects (VPIE) and triple-point isotope effects (TPIE) is briefly summarized for the noble gases (except He), and for selected diatomic molecules including oxygen. An approximate expression is derived to estimate the relative shift in the melting temperature with isotopic substitution. In general, the magnitude of the effects diminishes with increasing molecular mass and increasing temperature. Knowledge of the VPIE, molar volumes, and heat of fusion are sufficient to estimate the temperature shift or isotopic sensitivity coefficient via the derived expression. The usefulness of this approach is demonstrated in the estimation of isotopic sensitivities and uncertainties for triple points of xenon and molecular oxygen for which few documented estimates were previously available. The calculated sensitivities from this study are considerably higher than previous estimates for Xe, and lower than other estimates in the case of oxygen. In both these cases, the predicted sensitivities are small and the resulting variations in triple point temperatures due to mass fractionation effects are less than 20 μK.

Optical phonon and collective charge fluctuation induced superconductivity ofMgB2

In this paper, we undertake a quantitative analysis of observed parameters that influence the superconductingstate in MgB2. The analysis assumes a three-square-well model with three interactions, namely,the Coulomb, the electron–phonon and the electron charge fluctuations. Itis based on indirect-exchange Cooper pairing of electrons (quasiparticles)via ad hoc attractive charge fluctuations apart from those of phonons inMgB2. The relevant energy gap expressions in the formalism are solved byimposing experimental constraints on their solution (critical temperatureTc, isotope effectof 10B replaced by11B and pressurecoefficient of Tc).It is found that the indirect-exchange formalism provides a unique set of electronic parameters (electron–phonon(λphσ), electron charge fluctuation(λplσ), electron–electron(μσ) and Coulombscreening parameters (μσ*)) which, in particular, reproduce the dependence ofTc on the pressureP includingthe slope dTc/dP. The Tcσ ofMgB2 for two-dimensionalσ band carriers isestimated as 41 K for λphσ≈0.49, μ(μσ*)≈0.346 (0.19) andλplσ≈0.1. However we find areduction in Tcπ (21.6 K)for three-dimensional π band carriers with λphπ≈0.35, μ(μπ*)≈0.2 (0.115)and λplπ≈0.1. We comment on isotope coefficients for this system and draw further essential support forthe indirect-exchange mechanism adopted, via charge fluctuations.

Two-band superconductivity theory beyond the Migdal theorem

We propose a superconductivity theory of two-band nonadiabatic systems with strong electron correlations in the linear approximation in nonadiabaticity. Assuming a weak electron-phonon interaction, we obtain analytic expressions for the vertex and “intersecting” functions for each of the two bands. With the diagrams involving intersections of two electron-phonon interaction lines taken into account (which means going beyond the Migdal theorem), we determine mass operators of the Green’s functions and use them to derive the basic equations of the superconductivity theory for two-band systems. We find an analytic expression for the superconducting transition temperature Tc that differs from the expression in the case of the standard two-band systems by an essential renormalization of the relevant quantities that results from the nonadiabaticity effects and strong electron correlations. We study the dependence of Tc and of the isotopic coefficient α on the Migdal parameter m = ω0/eF and show that accounting for the overlap of energy bands on the Fermi surface and for the nonadiabaticity effects at small values of the transferred momentum (q ≪ 2pF) allows obtaining high values of Tc even for the weak electron-phonon interaction.

The charge carrier density effect on the superconductor parameters in a two-band model

The effect of the mobile charge concentration on the electron–phonon coupling constant, the band overlapping parameter and the isotopic coefficient is studied for a two-dimensional superconductor in a two-band model. This model is applied to describe the relation between the superconducting transition and the carrier density in CuO 2 layered superconductors, within the BCS framework. The experimental data for doping-induced charge in layered Hg-based cuprates are used to obtain numerical results.

Temperature Dependence of Isotope Effects in Uranium Chemical Exchange Reactions

Temperature dependence of isotope effects in U(IV)-U(VI) exchange reaction was experimentally studied by means of redox chromatography using columns packed with anion exchange resin in the temperature range 87- 160°C (360–433 K). The experimentally observed isotopic separation coefficient, ε, was converted to the isotopic equilibrium constant, 1n K-εo, of the U(IV)-U(VI) exchange reaction with the aid of the experimentally measured ionic mole fractions of U(IV) and U(VI) in the resin phase and the aqueous solution phase. The plots of εo vs. 1/T led to the temperature dependence of εo=0.69/T-82/T2 , where the first term is due to the nuclear field effect (nuclear-electron interaction effect) and the second term is due to the molecular-vibration mass effect. The discussion is extended to the temperature dependence of the previously reported isotope effects in the U(III)-U(IV) electron exchange reaction, and the U(VI)-malate-complex ligand exchange reaction.

Effects of lattice geometry and interaction range on polaron dynamics

We study the effects of lattice type on polaron dynamics using a continuous-time quantum Monte-Carlo approach. Holstein and screened Froehlich polarons are simulated on a number of different Bravais lattices. The effective mass, isotope coefficients, ground state energy and energy spectra, phonon numbers, and density of states are calculated. In addition, the results are compared with weak and strong coupling perturbation theory. For the Holstein polaron, it is found that the crossover between weak and strong coupling results becomes sharper as the coordination number is increased. In higher dimensions, polarons are much less mobile at strong coupling, with more phonons contributing to the polaron. The total energy decreases monotonically with coupling. Spectral properties of the polaron depend on the lattice type considered, with the dimensionality contributing to the shape and the coordination number to the bandwidth. As the range of the electron-phonon interaction is increased, the coordination number becomes less important, with the dimensionality taking the leading role.

Nonisothermal Brownian motion: Thermophoresis as the macroscopic manifestation of thermally biased molecular motion

A quiescent single-component gravity-free gas subject to a small steady uniform temperature gradient T, despite being at rest, is shown to experience a drift velocity UD=-D* gradient ln T, where D* is the gas's nonisothermal self-diffusion coefficient. D* is identified as being the gas's thermometric diffusivity alpha. The latter differs from the gas's isothermal isotopic self-diffusion coefficient D, albeit only slightly. Two independent derivations are given of this drift velocity formula, one kinematical and the other dynamical, both derivations being strictly macroscopic in nature. Within modest experimental and theoretical uncertainties, this virtual drift velocity UD=-alpha gradient ln T is shown to be constitutively and phenomenologically indistinguishable from the well-known experimental and theoretical formulas for the thermophoretic velocity U of a macroscopic (i.e., non-Brownian) non-heat-conducting particle moving under the influence of a uniform temperature gradient through an otherwise quiescent single-component rarefied gas continuum at small Knudsen numbers. Coupled with the size independence of the particle's thermophoretic velocity, the empirically observed equality, U=UD, leads naturally to the hypothesis that these two velocities, the former real and the latter virtual, are, in fact, simply manifestations of the same underlying molecular phenomenon, namely the gas's Brownian movement, albeit biased by the temperature gradient. This purely hydrodynamic continuum-mechanical equality is confirmed by theoretical calculations effected at the kinetic-molecular level on the basis of an existing solution of the Boltzmann equation for a quasi-Lorentzian gas, modulo small uncertainties pertaining to the choice of collision model. Explicitly, this asymptotically valid molecular model allows the virtual drift velocity UD of the light gas and the thermophoretic velocity U of the massive, effectively non-Brownian, particle, now regarded as the tracer particle of the light gas's drift velocity, to each be identified with the Chapman-Enskog "thermal diffusion velocity" of the quasi-Lorentzian gas, here designated by the symbol UM/M, as calculated by de la Mora and Mercer. It is further pointed out that, modulo the collective uncertainties cited above, the common velocities UD,U, and UM/M are identical to the single-component gas's diffuse volume current jv, the latter representing yet another, independent, strictly continuum-mechanical concept. Finally, comments are offered on the extension of the single-component drift velocity notion to liquids, and its application towards rationalizing Soret thermal-diffusion separation phenomena in quasi-Lorentzian liquid-phase binary mixtures composed of disparately sized solute and solvent molecules, with the massive Brownian solute molecules (e.g., colloidal particles) present in disproportionately small amounts relative to that of the solvent.

Polaronic and Nonadiabatic Phase Diagram from Anomalous Isotope Effects

Isotope effects (IEs) are powerful tools to probe directly the dependence of many physical properties on lattice dynamics. In this Letter we investigate the onset of anomalous IEs in the spinless Holstein model by employing the dynamical mean field theory. We show that the isotope coefficients of the electron effective mass and of the dressed phonon frequency are sizable also far away from the polaronic crossover and mark the importance of nonadiabatic lattice fluctuations. We draw a nonadiabatic phase diagram in which we identify a novel crossover, not related to polaronic features, where the IEs attain their largest anomalies.