Isotopic Selectivity Research Articles

Viability of hydrogen isotopes separation via heterolytic dissociation-driven Chemical Affinity Quantum Sieving on inexpensive alkali-earth oxides

The quest for economically viable strategies to separate hydrogen molecule isotopologues has recently provided clear indications on the design principles that ought to be implemented to satisfy the growing request for deuterium and tritium homodimers. In this respect, we investigate by electronic structure calculations whether easily obtainable, environmentally respectful, and inexpensive alkali-earth oxides may be suitable materials when it comes to separating hydrogen isotopologues. We found that hydrogen dimers heterolytically dissociate upon chemisorption on the most reactive three-coordinated vertex Mg, Ca, Sr and O sites, the formed species remaining in close proximity due to a strong H+/H– interaction. The inclusion of quantum zero point motion in the description of the adsorption energetics, mandatory if one wishes to differentiate the isotopologues behavior, indicated that the chemisorption energy becomes more negative the heavier the isotope involved. Isotopic selectivities estimated via Ideal Adsorbed Solution Theory (IAST) appear orders of magnitude higher than those previously presented. As chemisorbed species may catalyze an exchange reaction with gaseous molecules hinging on their nature as Broensted acid and Lewis base, we searched for possible processes competing with the desorption of vicinal adsorbed species; our results suggest that production of heterodimers (e.g. HD) is unlikely.

Inverse kinetic isotope effect of proton and deuteron permeation through pyridinic N-doped graphene

Graphene is becoming an increasingly popular platform for developing high-efficiency hydrogen isotope separation technologies operated at room temperature. However, its performance can be strongly affected by contributions from atomic defects. Understanding the influence of defects on the hydrogen isotope selectivity of graphene is thus imperative but remains elusive. In this work, we investigated the electrically driven proton/deuteron permeation through nitrogen-doped graphene membranes with varying N concentrations and configurations. The results show that N-doping significantly enhances the proton and deuteron permeability of graphene (by one order of magnitude). More importantly, deuterons are found to permeate faster through pyridinic N-containing defects than protons, demonstrating a pronounced inverse kinetic isotope effect (KIE) with kH/kD of 0.75. Conversely, pyrrolic N-containing defects exhibit a normal KIE (kH/kD = 1.56). The exclusive contribution of the pyridinic N to the inverse KIE is confirmed by the reversed KIE factor of the pyridinic N-dominated sample subjected to modification. Theoretical calculations indicate that the explicit dependence of KIE on N configuration originates from the different leading mechanisms of proton/deuteron permeation through these N-containing defects, which is governed by the size and the chemisorption imparted by defects. These findings provide fundamental insights into the correlation between defect characteristics and proton/deuteron transport in graphene, and contribute to developing economical hydrogen isotope separation technologies through the defect engineering of graphene.

Realization and simulations of the new SPES Beam Cooler

One of the aim of the new project Selective Production of Exotic Species (SPES) is to produce and select new, neutron reach, isotopes [1,2,3,4]. The technique adopted to produce these species is the Isotope Selection On Line (ISOL) that postpones the separation of the isotopes after the beam production, using a High-Resolution Mass Spectrometer (HRMS).In order to allow a good separation of isotopes , the transverse emittance and the energy spread of the beam should have very low values, for this reason the Beam Cooler (BC) is located between the ISOL target, i.e. the beam source, and the HRMS.In the SPES project, where heavy isotopes are expected (mass number >100), the spectrometer resolution must be preferably higher than dm/m = 5 × 10-5 and thus the features of the beam at the entrance of the HRMS should be at least εn 95% < 8.3 × 10-3 π mm mrad and σE < 1.5 eV.BC devices are devoted to improve the beam features in terms of emittance and energy spread. A new BC has been designed and realized by the Laboratoire de Physique Corpuscolaire (LPC) at Caen, France, for the SPES facility at Laboratori Nazionali di Legnaro (LNL), near Padova, Italy.BCs cool down the beam thanks to a dissipative process in which the thermal energy passes from the beam ions to another medium whose constituent is typically much lighter, Helium gas in our case. This process takes place inside a confinement system that on the one hand to limit the spread of the cooling medium, and on the other to allow the beam to continue along the required trajectory, in the presented device it is a row of radio frequency quadrupoles in an almost closed chamber.Some specifications of the BC described in this document: the RFQ is 723 mm long, its internal radius is 5 mm; the RFQ is included in the gas chamber which is 730 mm×280 mm×220 mm. Before it there is the injection part composed by, following the beam trajectory, a grounded pipe (388 mm long) and three focusing electrodes. On the opposite side there is the extraction part with two focusing electrodes.This document presents the main features of the new BC together with the results of a preliminary study where the beam dynamic has been simulated. The analysis embeds also the investigation of the gas distribution inside and outside the BC.The beam dynamic simulations are based on the Simion code [5] while the estimation of the gas distribution is computed with MolFlow+ [6].Simulations show that accurately setting the BC leads to a large improvement of the emittance while the energy spread still needs to be improved. Limiting the gas pressure in the acceleration zone seems to allow the required final boost.

A High‐Resolution Versatile Focused Ion Implantation Platform for Nanoscale Engineering

The ability to spatially control and modify material properties on the nanoscale, including within nanoscale objects themselves, is a fundamental requirement for the development of advanced nanotechnologies. The development of a platform for nanoscale advanced materials engineering (P‐NAME) designed to meet this demand is demonstrated. P‐NAME delivers a high‐resolution focused ion beam system with a coincident scanning electron microscope and secondary electron detection of single‐ion implantation events. The isotopic mass‐resolution capability of the P‐NAME system for a wide range of ion species is demonstrated, offering access to the implantation of isotopes that are vital for nanomaterials engineering and nanofunctionalization. The performance of the isotopic mass selection is independently validated using secondary ion mass spectrometry (SIMS) for a number of species implanted into intrinsic silicon. The SIMS results are shown to be in good agreement with dynamic ion implantation simulations, demonstrating the validity of this simulation approach. The wider performance capabilities of P‐NAME, including sub‐10 nm ion beam imaging resolution and the ability to perform direct‐write ion beam doping and nanoscale ion lithography, are also demonstrated.

Analytical HDR prostate brachytherapy planning with automatic catheter and isotope selection.

High dose rate (HDR) brachytherapy is commonly used to treat prostate cancer. Existing HDR planning systems solve the dwell time problem for predetermined catheters and a single energy source. Additional degrees of freedom can be obtained by relaxing the catheters' pre-designation and introducing more source types, and may have a dosimetric benefit, particularly in improving conformality to spare the urethra. This study presents a novel analytical approach to solving the corresponding HDR planning problem. The catheter and dual-energy source selection problem was formulated as a constrained optimization problem with a non-convex group sparsity regularization. The optimization problem was solved using the fast-iterative shrinkage-thresholding algorithm (FISTA). Two isotopes were considered. The dose rates for the HDR 4140 Ytterbium (Yb-169) source and the Elekta Iridium (Ir-192) HDR Flexisource were modeled according to the TG-43U1 formalism and benchmarked accordingly. Twenty-two retrospective HDR prostate brachytherapy patients treated with Ir-192 were considered. An Ir-192 only (IRO), Yb-169 only (YBO), and dual-source (DS) plan with optimized catheter location was created for each patient with N catheters, where N is the number of catheters used in the clinically delivered plans. The DS plans jointly optimized Yb-169 and Ir-192 dwell times. All plans and the clinical plans were normalized to deliver a 15Gy prescription (Rx) dose to 95% of the clinical treatment volume (CTV) and evaluated for the CTV D90%, V150%, and V200%, urethra D0.1cc and D1cc, bladder V75%, and rectum V75%. Dose-volume histograms (DVHs) were generated for each structure. The DS plans ubiquitously selected Ir-192 as the only treatment source. IRO outperformed YBO in organ at risk (OARs) OAR sparing, reducing the urethra D0.1cc and D1cc by 0.98% ( ) and 1.09% ( ) of the Rx dose, respectively, and reducing the bladder and rectum V75% by 0.09 ( ) and 0.13 cubic centimeters (cc) ( ), respectively. The YBO plans delivered a more homogenous dose to the CTV, with a smaller V150% and V200% by 3.20 ( ) and 1.91 cc ( ), respectively, and a lower CTV D90% by 0.49% ( ) of the prescription dose. The IRO plans reduce the urethral D1cc by 2.82% ( ) of the Rx dose compared to the clinical plans, at the cost of increased bladder and rectal V75% by 0.57 ( ) and 0.21 cc ( ), respectively, and increased CTV V150% by a mean of 1.46 cc ( ) and CTV D90% by an average of 1.40% of the Rx dose ( ). While these differences are statistically significant, the clinical differences between the plans are minimal. The proposed analytical HDR planning algorithm integrates catheter and isotope selection with dwell time optimization for varying clinical goals, including urethra sparing. The planning method can guide HDR implants and identify promising isotopes for specific HDR clinical goals, such as target conformality or OAR sparing.

Influence factors of lead in whole blood in the German External Quality Assessment Scheme by ICP-MS

To investigate the influence factors of lead in whole blood in the German External Quality Assessment Scheme(G-EQUAS) biological materials by inductively coupled plasma mass spectrometry(ICP-MS) from 2018 to 2020. ICP-MS was used to determine lead in whole blood of G-EQUAS by optimizing the reaction gas mode, sample dilution ratio, internal standard element, isotope and so on, analyzed the result. This study indicated that selection of internal standard elements, isotopes, matrix effect and physical effect may affect the accuracy of ICP-MS determination of lead in biological samples. Avoided the factors that may affect the result when determining lead in whole blood by ICP-MS.

Isotopologue pattern based data mining for selenium species from HILIC-ESI-Orbitrap-MS-derived spectra.

Automated and specific picking of selenium-containing molecular entities has not been an obvious option for software tools associated with electrospray high-resolution mass spectrometry (MS). In our study, a comprehensive pattern matching approach based on intra-isotopologue distance and isotopologue ratio data was critically evaluated in terms of reproducibility and selenium isotope selection on three samples, including selenized Torula yeast and the selenium hyperaccumulator plant Cardamine violifolia. Hydrophilic interaction liquid chromatography was applied to provide a one-step separation for water soluble metabolites to put an end to the need for either orthogonal setups or poor retention on reversed phase chromatography. Assistance from inductively coupled plasma-MS was taken only for chromatographic verification purposes, and the involvement of absolute mass defect (MD) data in selenometabolite-specific screening was assessed by multivariate statistical tools. High focus was placed on screening efficiency and on the validation of discovered selenized molecules to avoid reporting of artefacts. From the >1000 molecular entries detected, selenium-containing molecules were picked up with a recovery rate of >88% and a false positive rate of <10%. Isotop(ologu)e pairs of 78Se-80Se and 80Se-82Se proved to be the most performant in the detection. On the basis of accurate mass information and hypothetical deamination processes, elemental composition could be proposed for 72 species out of the 75 selenium species encountered without taking into account selenocompound databases. Absolute MD data were used to significantly differentiate a potentially sample-specific subgroup of false positive molecular entities from non-selenized and selenized entities.

Defining the Bounds of Using Radioactive Isotope Tracers to Sense Past Groundwater Recharge Under Transient State Conditions

AbstractAnalyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.

(Invited) Long-Term Stability of Electrochemical Hydrogen Isotope Separation Using Graphene Layers

Hydrogen isotope separation is vital for multiple application areas including nuclear energy sectors and nuclear weapons, and is fundamentally interesting. Two-dimensional (2-D) materials such as monolayer graphene have been demonstrated in the past to selectively transport ions including hydrogen isotopes through them which provides a pathway for membrane-based isotope separation. Recent studies have shown that monolayer graphene and other 2-D materials embedded in membrane electrode assemblies (MEAs) prepared from proton exchange membranes (PEMs) such as Nafion® can selectively transport protons at rates up to 14 times higher than deuterons. The mechanism for this unusually high isotope selectivity is still under study and is thought to involve transport at localized defects sites with one or more chemical steps having a high kinetic isotope effect. The long-term stability of electrochemical hydrogen isotope separation using monolayer graphene-based membranes is crucial for the graphene to become a good sieving layer candidate for large-scale hydrogen isotope separation. The focus of this study is on the long-term stability of separating characteristics of graphene layers embedded in MEAs that actively pump protons and deuterons through them over an extended period of time. Initial results suggest that graphene embedded within Nafion sandwiches in their current form have a high isotope selectivity initially but that isotope selectivity can diminish as current is passed through the sandwich structures for extended time periods. Findings from chronoamperometry experiments performed on graphene-embedded MEAs while interchanging H2 and D2 gas feeds in symmetric electrochemical H/D pump cells, and potential factors affecting separation capability over long periods of time, will be discussed during the talk.

Laser-induced isotope selective photoionization of atomic samarium

Resonance ionization spectroscopy of samarium has been performed in an atomic beam in conjunction with a time-of-flight mass spectrometer. Isotope selective photoionization studies have been carried out on one of the even isotopes of samarium (152Sm). High degree of isotopic selectivity (> 95%) has been achieved experimentally for 152Sm using multi-mode dye lasers. Isotopic abundance of 152Sm in mass selective photoionization has been studied as a function of excitation laser energy density. By employing isotope selective photoionization spectroscopy, the isotope shifts for the first- and second-step transitions have also been determined.

Strong isotopic selectivity on dication formation of benzene

Double ionization of benzene initiates a competition between its fragmentation driven by Coulomb repulsion and dication stabilization, in which the molecule undergoes a strong geometric rearrangement. We find experimentally that stabilization following an electron-impact-induced double-ionization is remarkably sensitive to the isotopic replacement of just one $^{13}\mathrm{C}$ atom in the benzene ring. This result has no analog in dications of smaller molecules. The large reactivity of medium-size hydrocarbon dications points towards an alternative route to imprint isotopic signatures in astrophysical processes.

Laser double optical resonance excitation-ionization of Mo with optogalvanic detection

We report on the first measurement of resonant three-step, two-colour ionization of atomic molybdenum, using a hollow cathode lamp (HCL) with optogalvanic detection. Wavelength scans were made for two specific transitions involved in the ionization pathways under investigation, namely 4d5(6S)5s 7S3–4d5(6S)5p 7P4 and 4d5(6S)5p 7P4–4d5(6S)6d 7D5. So-called ‘slow’ and ‘fast’ optogalvanic signals were respectively observed for each resonant quantum jump and for the simultaneous excitation of the two laser frequencies. This successful detection confirms the HCL as a cost effective spectroscopic investigation tool. In particular its use in the optogalvanic mode of operation allows one to precisely, easily and reliably tune the wavelength of one or more lasers to resonances of interest for experiments in the general domain of atomic vapour laser isotope selection (AVLIS). This activity has been undertaken in the framework of the Selective Production of Exotic Species (SPES) project at the ISOL facility of the Legnaro National Laboratories of INFN. These measurements are a necessary step towards the realization of the MOLAS subproject of SPES, whose aim is to verify the production of 99m technetium for medical application via laser ionization of the 99 uma isotope of Molibdenum.

Investigation of Molecular Interferences at GDMS Analysis of Main Elements and Microalloing of High-Entropy Alloy AlCrFeCoNiCu

The peculiarities of the glow discharge mass-spectrometry (GDMS) analysis of the main components and elements of microalloying of high-entropy AlCrFeCoNiCu alloy are considered in the paper. Molecular interferences of ArxAy+i, ArxG+i, AxBy+i types (where A, B are the components of the sample, G are single and 2-3 atomic gases; x, y = 1, 2, i - charge of ion, i = 1, 2), which are formed during cathode sputtering of this alloy in glow discharge plasma were calculated and experimentally tested. It is shown for spectrometers at resolution R0.5 ≥ 7000, the greatest influence of molecular ions of Me2+ and ArMe+ types exist in the range of isotope masses from 85Rb to about 107Ag. A careful selection of isotopes is required in this mass range to meet detection limit conditions. In other areas of the mass spectrum, the sensitivity of the analysis is limited by the background current and the sensitivity of the detectors and is at the usual ppb-level for this method.

Analysis of ENRESA BWR samples: nuclide inventory and decay heat

In this paper the isotopic compositions from 8 Boiling Water Reactor samples are analyzed following different irradiation assumptions as well as different simulation tools. These samples are part of a proprietary experimental program by a Spanish consortium, and they were obtained from a GE14 assembly irradiated in Sweden. Calculated nuclide concentrations are compared with measured ones providing biases for a selection of isotopes and samples; calculated uncertainties are also provided. Finally, the decay heat from one the sample segment is calculated and compared among the different simulation assumptions. It is shown that depending on the considered nuclear data library and modeling, different contributors affect the calculated quantities, indicating a certain level of prediction power.

Separation of manganese isotopes by resonance ionization mass spectrometry for 53Mn half-life determination

We report on the production of ultra-pure samples of the long-lived radioisotope 53Mn for precision measurements of its half-life. Activated samples from a copper beam dump from PSI, which was irradiated with 590 MeV protons, were used for extraction of the manganese fraction. Following initial radiochemical purification, efficient three-photon laser resonance ionization of manganese inside a hot-cavity laser ion source was applied for subsequent isotope selection in a 30 keV high transmission magnetic mass separator. A new ionization scheme was developed and characterized for 53Mn implantation. In this way the isobar 53Cr and the Mn isotopes 54,55Mn are quantitavely removed, with a special focus on the radioactive 54Mn isotope. Microgram quantities of 53Mn were implanted into Al targets with an isotopic and isobaric purity of well above 103. An overall efficiency of the enrichment process of about 15% was demonstrated.

Fusion Visualization Technique to Improve a Three-Dimensional Isotope-Selective CT Image Based on Nuclear Resonance Fluorescence with a Gamma-CT Image

One of the most noteworthy aspects of computed tomography (CT) based on the nuclear resonance fluorescence (NRF) transmission method is the isotope selectivity that makes it possible to discern an isotope of interest from other isotopes within a sample. We experimentally obtained a three-dimensional (3D) isotope-selective CT image based on the NRF transmission method (3D NRF-CT) for the enriched lead isotope distribution of 208Pb in a cylindrical holder in a previous study. The cylindrical holder’s diameter and height are 25 mm and 20 mm, respectively. The NRF-CT imaging technique requires a considerable data accumulation time. It took 48 h to obtain an image with a resolution of 4 mm/pixel in the horizontal plane and 8 mm/pixel in the vertical plane using a laser Compton scattering (LCS) gamma-ray beam with a beam size of 2 mm and a flux density of 10 photons/s/eV. Improving the NRF-CT image resolution with the existing hardware is challenging. Therefore, we proposed an alternative method to improve the NRF-CT image resolution using the fusion visualization (FV) technique by combining the NRF-CT image including isotopic information with a gamma-CT image, which provides better pixel resolution. The 3D gamma-CT image for the same sample was measured at the same beamline BL1U in the ultraviolet synchrotron orbital radiation-III (UVSOR-III) synchrotron radiation facility at the Institute of Molecular Science at the National Institutes of Natural Sciences in Japan under similar experimental conditions except for the LCS gamma-ray beam flux and beam size. Obtaining a 3D gamma-CT image with a resolution of 1 mm/pixel took 5 h using an LCS gamma-ray beam with a beam size of 1 mm and a flux density of 0.7 photons/s/eV. The data processing of the FV technique has been developed, and the 3D NRF-CT image quality was improved.

Effects of partial crystallization on the glassy slowdown of aqueous ethylene glycol solutions

Combining differential scanning calorimetry, nuclear magnetic resonance, and broadband dielectric spectroscopy studies, we ascertain the glass transition of aqueous ethylene glycol (EG) solutions, in particular the effects of partial crystallization on their glassy slowdown. For the completely liquid solutions in the weakly supercooled regime, it is found that the dynamics of the components occur on very similar time scales, rotational and translational motions are coupled, and the structural (α) relaxation monotonously slows down with increasing EG concentration. Upon cooling, partial crystallization strongly alters the glassy dynamics of EG-poor solutions; in particular, it strongly retards the α relaxation of the remaining liquid fraction, causing a non-monotonous concentration dependence, and it results in a crossover from non-Arrhenius to Arrhenius temperature dependence. In the deeply supercooled regime, a recrossing of the respective α-relaxation times results from the Arrhenius behaviors of the partially frozen EG-poor solutions together with the non-Arrhenius behavior of the fully liquid EG-rich solutions. Exploiting the isotope selectivity of nuclear magnetic resonance, we observe different rotational dynamics of the components in this low-temperature range and determine the respective contributions to the ν relaxation decoupling from the α relaxation when the glass transition is approached. The results suggest that the ν process, which is usually regarded as a water process, actually also involves the EG molecules. In addition, we show that various kinds of partially crystalline aqueous systems share a common relaxation process, which is associated with the frozen fraction and differs from that of bulk hexagonal ice.

High Spatial Resolution Neutron Transmission Imaging Using a Superconducting Two-Dimensional Detector

Neutron imaging is one of the most powerful tools for nondestructive inspection owing to the unique characteristics of neutron beams, such as high permeability for many heavy metals, high sensitivity for certain light elements, and isotope selectivity owing to a specific nuclear reaction between an isotope and neutrons. In this study, we employed a superconducting detector, current-biased kinetic-inductance detector (CB-KID) for neutron imaging using a pulsed neutron source. We employed the delay-line method, and high spatial resolution imaging with only four reading channels was achieved. We also performed wavelength-resolved neutron imaging by the time-of-flight method for the pulsed neutron source. We obtained the neutron transmission images of a Gd–Al alloy sample, inside which single crystals of GdAl <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> were grown, using the delay-line CB-KID. Single crystals were well imaged, in both shapes and distributions, throughout the Al–Gd alloy. We identified Gd nuclei via neutron transmissions that exhibited characteristic suppression above the neutron wavelength of 0.03 nm. In addition, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd resonance dip, a dip structure of the transmission caused by the nuclear reaction between an isotope and neutrons, was observed even when the number of events was summed over a limited area of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m × 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. Gd selective imaging was performed using the resonance dip of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd, and it showed clear Gd distribution even with a limited neutron wavelength range of 1 pm.

Insertion products in the reaction of carbonyl oxide Criegee intermediates with acids: Chloro(hydroperoxy)methane formation from reaction of CH2OO with HCl and DCl

The reactions of carbonyl oxide Criegee intermediates with acids proceed predominantly by an insertion mechanism. We characterise the products from one of the simplest reactions of carbonyl oxides with inorganic acids, CH2OO + hydrogen chloride, which occurs via a 1,2-insertion in the H–Cl bond. Reactions of both HCl and DCl isotopologues yield product signal at the mass of the insertion product chloro(hydroperoxy)methane and a dissociative ionisation peak at the mass of the protonated (or deuteronated) Criegee intermediate. The isotopic composition of the insertion product has been measured for reaction mixtures where both HCl isotopologues are present, and the H/D ratio of the product is consistently higher (by a factor of 1.6 ± 0.3) than that of the reactants. This isotope selectivity in the products has smaller uncertainty than the ratio of measured rate coefficients and suggests a normal (k H > k D) kinetic isotope effect in the reaction. Theoretical kinetics calculations predict a small normal kinetic isotope effect for the overall reaction (k H / k D = 1.35 at 20 Torr N2 and k H / k D = 1.2 at 1 atm N2) but predict a substantial inverse kinetic isotope effect (k D > k H) for the stabilisation fraction, in disagreement with the experimental observation.

The Intermolecular NOE Depends on Isotope Selection: Short Range vs Long Range Behavior.

The nuclear Overhauser effect (NOE) is a powerful tool in molecular structure elucidation, combining the subtle chemical shift of NMR and three-dimensional information independent of chemical connectivity. Its usage for intermolecular studies, however, is fundamentally limited by an unspecific long-ranged interaction behavior. This joint experimental and computational work shows that proper selection of interacting isotopes can overcome these limitations: Isotopes with strongly differing gyromagnetic ratios give rise to short-ranged intermolecular NOEs. In this light, existing NOE experiments need to be re-evaluated and future ones can be designed accordingly. Thus, a new chapter on intermolecular structure elucidation is opened.