Calculations of Thermodynamic Sulfur Isotope Effect

The isotopic reduced partition function ratios (RPFR), (s/s')f, for the ³⁴S/³²S isotopic pair were calculated for 24 sulfur compounds between 10 and 2,000K. Their magnitudes were in the following sequences; at low enough temperatures at which In(s/s')f depends only on the isotopic difference in frequency-sum, SF₆>SO₂F₂>SF₅Cl>SF₅Br>SO₄ ^2->SO₂Cl₂>SO₃>NSF₃>SF₄>SOF₂>SOCl₂>Me₂SO>SOBr₂>SO₂>SPBr₃>SCBr₂>Me₂S>SPCl₃>SCCl₂>SCF₂>SPF₃>CS₂>OCS>H₂S, and at high enough temperatures at which In(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO₂F₂>SO₄ ^2->SO₃>SF₆>SO₂Cl₂>SF₅C1>NSF₃>SF₅Br>SOF₂>SO₂>SF₄>Me₂SO>SCCl₂>SOBr₂>H₂S>Me₂S>CS₂>SCF₂>OCS<SCCl₂>SCBr₂>SPF₃>SPCl₃>SPBr₃ where Me--CH₃. Correlation of the RPFR with molecular structure and molecular forces was discussed.

The equilibrium constants K for the ³⁴S/³²S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two types of temperature dependences were observed; one being smooth monotonic and the other having single cross-over with no pre-inflection.     

Uranium Isotope Separation by Cation Exchange Chromatography Using Uranous Sulfate Complexes

A nearly ideal displacement chromatography has been realized with an eluent of MgS0₄ and H₂SO₄ in the study of uranium isotope separation by means of cation exchange chromatography using uranous sulfate complexes. Uranium-235 was enriched at the end of the chromatogram and ²³⁸U was enriched at the front. Two long distance displacement experiments have been carried out, keeping an isotopic plateau region on the chromatogram. Consequently, good accumulation of the isotopic fractionation based on uranous-sulfate complex formation reactions obtained. The separation coefficient ε of this system was estimated to be about 5×10^?5.     

Reduced Partition Function Ratio of Uranyl Ion and Uranium Isotope Effect

Density of 30v/o tri-n-butyl phosphate-n-dodecane solution loaded with uranyl nitrate, nitric acid and water was measured. An empirical density equation was derived from regression analysis of the density data. The equation represents the density values well in a wide range of composition and temperature.     

Ab initio Quantum Chemical Study on Charge Distribution and Molecular Structure of Uranyl (VI) Species with Raman Frequency

Ab initio molecular orbital calculation was performed for uranyl (VI) monomer and dimer complexes with some water molecules and/or hydroxide ions. The Raman active frequencies were calculated for each complex after structural optimization in vacuum state, and investigated the molecular structure and the charge distribution. For uranyl monomer, the calculated Raman frequencies for uranyl with 5 or 6 water molecules show good agreement with experimental Raman frequencies for uranyl hydrates. On the contrary, the calculation underestimates the Raman frequency in case of hydroxide ions in uranyl complex. The calculation models for uranyl dimer were made from [UO₂(H₂O)₅]²⁺, then the hydroxide ions bridging model, [(UO₂)₂(OH)₂(H₂O)₆]²⁺, is more stable than water molecules bridging, [(UO₂)₂(H₂O)₈]⁴⁺, and the theoretical Raman frequency and uranyl bond lengths have the good coincidence with those of experiments. The calculated uranyl bond length of dimer is slightly longer than that of monomer. Also, the charge of oxygen atom in uranyl shows larger change than that of uranium atom between dimer and monomer. And this charge distribution is mostly influenced by the charge donation of ligands. If only same ligands are surrounding, the number of ligands influenced this charge distribution.     

Isotope Effects in Electrolytic Formation of Lithium Amalgam

Isotope effects in the lithium amalgam formation were studied by using the mercury cathode and LiOH solutions. The electrolyses were carried out at different conditions of both applied voltages 4–10 V, and the concentrations of initially charged LiOH, 0.5–5 mol/dm³. Higher efficiency of electrolytic amalgam formation was observed at higher LiOH concentrations and higher applied voltages. At these conditions, however, significant amount of solid amalgam was produced in the mercury phase. From the isotopic analyses on the samples taken during the electrolyses, it was found that the isotopic equilibrium was attained between the aqueous and the liquid amalgam phases. The isotopic equilibrium constant (isotope separation factor) was determined as 1.056 (average value for all the experiments) at 20°C.     

Rapid-Swept CW Cavity Ring-down Laser Spectroscopy for Carbon Isotope Analysis

With the aim of developing a portable system for an in field isotope analysis, we investigate an isotope analysis based on rapid-swept CW cavity ring-down laser spectroscopy, in which the concentration of a chemical species is derived from its photo absorbance. Such a system can identify the isotopomer and still be constructed as a quite compact system. We have made some basic experimental measurements of the overtone absorption lines of carbon dioxide (¹²C¹⁶O₂, ¹³C¹⁶O₂) by rapid-swept cavity ring-down spectroscopy with a CW infrared diode laser at 6,200 cm^?1(1.6)mm). The isotopic ratio has been obtained as (1.07±0.13)x 10^?2, in good agreement with the natural abundance within experimental uncertainty. The detection sensitivity in absorbance has been estimated to be 3x 10^?8cm^?1.     

Zinc Isotope Fractionation on Benzo-15-crown-5 Resin by Liquid Chromatography

Chromatographic fractionation of zinc isotopes was performed on the synthesized benzo-15-crown-5 resin as a column packing material at 323K in the breakthrough manner for both a frontal and a rear bands. Zinc adsorption capacity was affected by anion chloride concentration and solvent dielectric constant. The heavier zinc isotopes were found enriched to the solution phase and the lighter zinc isotope was concentrated on the resin phase. The frontal maximum enrichment ratio for isotopic pair of ⁶⁸Zn/⁶⁴Zn was 1.0081. The isotope separation coefficients for isotopic pair of ⁶⁸Zn/⁶⁴Zn for frontal and rear band, were 5.3 × 10^?4, 4.5 × 10^?4, respectively.     

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H₂=H₂O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D₂=D₂O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H₂O/D₂, D₂O/H₂, H₂O/HDO/H₂ or H₂O/D₂O/HDO/H₂ to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.     

Carbon and Oxygen Isotope Separation by Plasma Chemical Reactions in Carbon Monoxide Glow Discharge

The separation of carbon and oxygen isotopes in CO glow discharge has been studied. The isotope enrichment in the products was measured by quadru-pole mass spectrometer. The reaction yield and empirical formula of solid phase products were determined by the gas-volumetric analysis. The stable products obtained in our experiment are CO₂ and solid polymers formed on the discharge wall. The polymer consists of both carbon and oxygen and the oxygen/carbon mole ratio in the polymer is 0.35±0.05. The isotope enrichment coefficients show a strong negative dependence on discharge current though the relative reaction yields have an opposite tendency. Consequently, the maximum isotope enrichment coefficients for ¹³C in wall deposit of 2.31 and for ¹⁸O in CO₂ of 1.37 are obtained when the discharge current and the reaction yields are minimum in our experimental range. The experimental results of isotope enrichment have been compared with theoretical values estimated by an analytical model of literature. The dilution mechanism of the isotope enrichment of stable products is inferred from the isotopic distributions of ¹³C and ¹⁸O in products and theoretical predictions for isotope enrichment.     

Reduced partition function ratios of hydrogen species adsorbed on platinum cluster Pt19 studied by density functional theory

Geometry optimization and estimation of H/D reduced partition function ratios (RPFRs) of Pt₁₉–H, Pt₁₉–H⁺, Pt₁₉–H₂, and Pt₁₉–H₂⁺ models of hydrogen species adsorbed on surfaces of metallic platinum particles, were carried out based on the density functional theory. Two types of optimized structures were obtained for Pt₁₉–H and Pt₁₉–H⁺, and three for Pt₁₉–H₂ and Pt₁₉–H₂⁺. Stabilization energy consideration suggested that the most probable structure for Pt₁₉–H and Pt₁₉–H⁺ is the one in which H/H⁺ is bonded to a Pt atom, and that for Pt₁₉–H₂ and Pt₁₉–H₂⁺ is the one in which two H/H⁺s are bonded to two adjacent Pt atoms with no direct bonding between the two H/H⁺s. The value of RPFR obtained for those structures ranged from 3.9303 to 4.4014 at 25 °C. Interaction between two adjacent H–Pt bonds seems to slightly enhance the mutual RPFR values.     

ABSTRACTS OF 1993 AESJ AWARDS

The UB3LYP/LanL2DZ level calculations were carried out for sixty-seven Li-M diatomic molecules of lithium between LiH and LiBi to explore the periodic properties of their ⁶Li-to-⁷Li isotopic reduced partition function ratios (rpfrs) and some other quantities. The Li-M bond distance, the frequency shift upon ⁷Li/⁶Li isotope substitution and the rpfr all show plots typical of any chemical and physical property which is a periodic function of the atomic number. The rpfr is strongly correlated with the Li-M bond stretching force constant except for LiH. The present calculations show that the rpfrs of diatomic molecules of group 2, group 12 and group 18 elements are relatively small, which reflects the filled electron shell and subshell characters of those elements. The results of the calculations and the consideration on chemical properties of elements suggest that zinc is a possible substitute for mercury in lithium isotope separation processes utilizing the redox reaction of lithium.     

Strontium Isotope Effect in Liquid-Liquid Extraction of Strontium Chloride Using a Crown Ether

Isotope effects in a liquid-liquid extraction of strontium with dicyclohexano-18-crown-6 (DC18C6) were investigated. Unit mass enrichment factors were observed to increase with concentrations of strontium salt in an aqueous phase. Isotope distinguishing ability of DC18C6 to strontium isotopes was calculated as an intrinsic separation factor to be K _c =1.00051±0.00004. An odd mass number isotope, ⁸⁷Sr, was recognized to behave differently from even mass number isotopes, ⁸⁴Sr, ⁸⁶Sr and ⁸⁸Sr. The enrichment factor induced by a nuclear property (odd or even mass number) other than the mass difference was ε_O/E = ?8.0 × 10^?4 which was observed with 3.2M Sr aqueous solution. Isotope shift of energy state for 5S-orbital of strontium produces the isotope shift in vibrational energy between the strontium ion and the DC18C6.     

Researches on Laser Isotope Separation of Gadolinium and Boron

Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. ¹⁰BCl₃ was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO₂ laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation.     

Selectivity Loss Due to Magnetic Field in Laser Isotope Separation of Gadolinium Based on Polarization Selection Rules

The magnetic field effect on the isotopic selectivity with J=2→2→1→0 multistep photoionization was studied by the experiment and the numerical analysis. Three linearly polarized dye laser pulses were used to photoionize the atomic gadolinium and the isotopic selectivity was measured by changing the magnetic field strength and the angle between the laser polarization and the magnetic field. The experimental data was reproduced well by the numerical simulation. From the oscillatory behavior of the isotopic selectivity, the Lande factor of the high-lying excited level (34,586.7 cm^-1) of atomic gadolinium was determined.     

Gadolinium Isotope Separation by Cation Exchange Chromatography

Displacement chromatographies of Gd adsorption band in cation exchange resin were performed to observe the isotope effects in the Gd ion exchange processes involving complex forming reagents. The heavy isotope of ¹⁶⁰Gd was found to be enriched at the front boundary of Gd adsorption band and the lighter isotopes of 1MGd, ¹⁵⁶Gd and ¹⁵⁷Gd were enriched at the rear boundary in both cases of 20.1m elution with EDTA and 14 m elution with malic acid, as predicted in the theoretical relations. Observed separation coefficients are 4.9×10^?5, 4.0×10^?5 and 2.5×10^?5for isotopie pairs of ^{156 160}Gd, ¹⁵⁸Gd and ¹⁶⁰Gd, respectively, in the case of EDTA elution. In the case of malic acid elution, smaller separation coefficients were observed as 1.8×10^?5, 1.6 ⁵O^?5 and 0.92×10^?5 for isotopie pairs of ^{156 160}Gd, ¹⁵⁷Gd and^{158 160} respectively.     

Radiation oxidation of tetravalent uranium solutions

Treatment of a sulfuric acid solution of tetravalent uranium. containing 0.8 N H₂SO₄, in the absence of O₂ and at a concentration of U⁺⁴ 100 mg-equiv/liter, with Co⁶⁰ -radiation gave an oxidation yield of U⁺⁴ close to 5.0. U⁺⁴ was not oxidized by the molecular ion H ₂ ⁺ even with greatly increased acidity of the solution and a decreased U⁺⁴ concentration. A decrease in U⁺⁴ concentration resulted in a lower yield mainly due to recombination of the H and OH radicals. An equation for the relation of G to [U⁺⁴] is put forward which agrees with experimental data, and a ratio involving the rate constants of the three reactions H + OH, H + H and U⁺⁴ + OH was found. A decrease in the yield G was observed on increasing the U⁺⁴ concentration above 110 mg-equiv/liter. This phenomenon is apparently explained by the reduction of U⁺⁴ radicals by H. We considered, some mechanism by which uranyl ions may retard U⁺⁴ oxidation. As a result of this consideration we were able to calculate the ratio of the rate constants of the reactions UO ₂ ⁺² + H and H + H and a ratio involving the rate constants of the reactions UO ₂ ⁺² + OH, H + OH and H + H.An equation based on the mechanism suggested for the oxidation of tetravalent uranium in dilute solution in the presence of uranyl ion has been deduced for the relation of G to [U⁺⁴] and [UO ₂ ⁺² ] and this agrees with the experimental data for a wide range of concentrations.     

Calcium isotope separation by band chromatography using 18-crown-6-ether resin

To develop the ⁴⁸Ca enrichment process, a feasibility study on a band chromatography was made using 9 M HCl solution and crown ether resin synthesized in porous silica beads. Prior to the chromatographic experiments, distribution coefficients, Kd, of Ca²⁺ and Sr²⁺ were measured at different concentrations of these ionic species. The frontal boundary of the chromatography was made by a usual manner of the breakthrough mode of calcium feeding, and the rear boundary was made by introducing strontium as a following ion on the basis of the observed Kd values. It was confirmed that the heavy isotope ⁴⁸Ca was depleted in the rear boundary region, while ⁴⁸Ca was enriched in the front boundary region. The values of separation coefficient ε (= α – 1) in three chromatographic operations at different temperatures were observed as 2 × 10^?3 ~ 3 × 10^?3. The separation coefficients observed in the front boundary regions, where ⁴⁸Ca was enriched, agreed with those observed in the rear boundary regions, where ⁴⁰Ca was enriched.     

Precipitation Reaction of Uranyl Ion in Molten Potassium Thiocyanate

The qualitative and the quantitative analyses of the reaction products obtained by heating uranyl solution of molten potassium thiocyanate were carried out. It was found that in the presence of water in the melt, uranyl ion is converted into UO₂ accompanied with the evolution of CO₂ and the formation of free sulfur. The molar ratios on these products were almost equal to each other.

By detecting ammonia in reaction products, it was concluded that the precipitation reaction of uranyl ion in the melt is expressed as follows:

UO₂ ⁺⁺ + SCN^? + 2H₂O = UO₂ + CO₂ +S+ NH₄ ⁺.     

基于光化学锂同位素分离条件的同位素比率测量

从光化学锂同位素分离实验研究的需求出发,基于其分离条件,提出了一种测量锂同位素比率的方法。该方法利用锂原子蒸气对探测光吸收峰的峰值来计算锂的同位素比率,避开了测量原子密度时所需的吸收信号频率定标与光强随频率变化积分中积分限的选择问题。该方法还根据锂同位素吸收谱的特殊性采用具有较强吸收效应的⁶Li的D₂线对应的吸收峰峰值,可在原子蒸气中⁶Li含量较低时提高对比率的测量精度。设计并搭建了实验装置,对该方法进行了测试。同一条件下所测得的同位素比率相对标准偏差小于1%,表明该方法对光化学分离方法中锂同位素比率相对变化是敏感的。这意味着该方法可作为以原子蒸气为分离介质的激光锂同位素分离研究的诊断手段。     

Zinc Isotope Effects Observed by Liquid Chromatography with Benzo-15-Crown-5 Resin

The chromatographic fractionation in Zn isotopes was performed on the synthesized benzo-15-crown-5 resin at 313 and 343 K. The lighter isotopes were found enriched in the resin phase. The isotope fractionation coefficients (ε) were 3.4 and 2.9×10^?4, 4.7 and 4.7×10^?4, and 6.7 and 5.7×10^?4 for the ⁶⁶Zn/⁶⁴Zn, ⁶⁷Zn/⁶⁴Zn and ⁶⁸Zn/⁶⁴Zn isotopic pairs at 313 and 343 K, respectively. They reflected mass-dependence among the Zn isotopes at each operated temperature but did not show 1/T² -temperature proportionality. The temperature effects of the composition of Zn species both in the solution phase and in the resin phase may account in part for the latter observation. The magnitudes of ε's in this study were comparable to the ones obtained by ion exchange chromatography, but much smaller than those observed in the solvent extraction systems with a crown ether in the organic phase.