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The microwave spectra of three isotopologues of the gas-phase heterodimer formed between cis-1,2-difluoroethylene and hydrogen chloride are obtained in the 5–21 GHz region using Fourier transform microwave spectroscopy. The molecular structure, determined from the analysis of the spectra and supported by quantum chemistry calculations, has the hydrogen atom of the hydrogen chloride molecule interacting with both fluorine atoms of the fluoroethylene and no interaction between the chlorine atom and the olefin. Although the equilibrium structure has two inequivalent H⋯F interactions, zero-point motion averages over the two equivalent choices for these interactions, rendering the pairs of like atoms (C, H, and F) of the fluoroethylene equivalent, retaining the C2v symmetry of the olefin. This results in only one unique singly substituted 13C isotopologue and in the observed effects on transition intensities due to nuclear spin statistics. The heterodimer structure allows for a strong, linear hydrogen bond between the HCl donor and the fluoroethylene acceptor that is more important here than in the analogous acetylene containing complex, where the interaction between the π electrons of acetylene and an electrophilic hydrogen atom on the olefin compensates for the loss of linearity required for binding to a geminal F/H pair. [ABSTRACT FROM AUTHOR]

Improved two-body and three-body potentials for helium have been used to calculate from first principles the third density and acoustic virial coefficients for both 4He and 3He. For the third density virial coefficient C(T), uncertainties have been reduced by a factor of 4–5 compared to the previous state of the art; the accuracy of first-principles C(T) now exceeds that of the best experiments by more than two orders of magnitude. The range of calculations has been extended to temperatures as low as 0.5 K. For the third acoustic virial coefficient γa(T), we applied the Schlessinger point method, which can calculate γa and its uncertainty based on the C(T) data, overcoming some limitations of direct path-integral calculation. The resulting γa are calculated at temperatures down to 0.5 K; they are consistent with available experimental data but have much smaller uncertainties. The first-principles data presented here will enable improvement of primary temperature and pressure metrology based on gas properties. [ABSTRACT FROM AUTHOR]

Chloromethane, CH3Cl, is the first organohalogen molecule to be detected in the interstellar medium. Using the recently generated accurate three-dimensional potential energy surface (3D-PES) for the weakly bound CH335Cl–He complex, we deduced that of CH337Cl–He. Both 3D-PESs were incorporated later into dynamical computations code for nuclear motions treatments of each isotopologue colliding with He. We determined the state-to-state (de-)excitation cross sections for transitions among the 105 lowest rotational levels of both ortho-CH335Cl and ortho-CH337Cl (up to jkɛ = 206±). For total energies up to 100 cm−1, we used the quantum close-coupling methodology, and we adopted the coupled state approach for higher energies (up to 2500 cm−1). Rate coefficients for temperatures ranging from 5 to 150 K are then deduced after averaging these cross sections over a Maxwell–Boltzmann velocity distribution. Computations show that isotopic effects are weak, validating the use of collision rates of ortho-CH335Cl for ortho-CH337Cl and vice-versa. However, we expect that our results will be helpful to accurately determine the abundances of these isotopologues in the interstellar medium and, more generally, for understanding the complex and still not fully elucidated chemistry of chlorine containing molecular species there. [ABSTRACT FROM AUTHOR]

The gas-phase rotational spectrum from 8 to 750 GHz and the high-resolution infrared (IR) spectrum of pyridazine (o-C4H4N2) have been analyzed for the ground and four lowest-energy vibrationally excited states. A combined global fit of the rotational and IR data has been obtained using a sextic, centrifugally distorted-rotor Hamiltonian with Coriolis coupling between appropriate states. Coriolis coupling has been addressed in the two lowest-energy coupled dyads (ν16, ν13 and ν24, ν9). Utilizing the Coriolis coupling between the vibrational states of each dyad and the analysis of the IR spectrum for ν16 and ν9, we have determined precise band origins for each of these fundamental states: ν16 (B1) = 361.213 292 7 (17) cm−1, ν13 (A2) = 361.284 082 4 (17) cm−1, ν24 (B2) = 618.969 096 (26) cm−1, and ν9 (A1) = 664.723 378 4 (27) cm−1. Notably, the energy separation in the ν16-ν13 Coriolis-coupled dyad is one of the smallest spectroscopically measured energy separations between vibrational states: 2122.222 (72) MHz or 0.070 789 7 (24) cm−1. Despite ν13 being IR inactive and ν24 having an impractically low-intensity IR intensity, the band origins of all four vibrational states were measured, showcasing the power of combining the data provided by millimeter-wave and high-resolution IR spectra. Additionally, the spectra of pyridazine-dx isotopologues generated for a previous semi-experimental equilibrium structure (reSE) determination allowed us to analyze the two lowest-energy vibrational states of pyridazine for all nine pyridazine-dx isotopologues. Coriolis-coupling terms have been measured for analogous vibrational states across seven isotopologues, both enabling their comparison and providing a new benchmark for computational chemistry. [ABSTRACT FROM AUTHOR]

Modified WKB theory for calculating tunneling splittings in symmetric multi-well systems in full dimensionality is re-derived using Cartesian coordinates. It is explicitly shown that the theory rests on the wavefunction that is exact for harmonic potentials. The theory was applied to calculate tunneling splittings in vinyl radical and some of its deuterated isotopologues in their vibrational ground states and the low-lying vibrationally excited states and compared to exact variational results. The exact results are reproduced within a factor of 2 in most states. Remarkably, all large enhancements of tunneling splittings relative to the ground state, up to three orders in magnitude in some excited mode combinations, are well reproduced. It is also shown that in the asymmetrically deuterated vinyl radical, the theory correctly predicts the states that are localized in a single well and the delocalized tunneling states. Modified WKB theory on the minimum action path is computationally inexpensive and can also be applied without modification to much larger systems in full dimensionality; the results of this test case serve to give insight into the expected accuracy of the method. [ABSTRACT FROM AUTHOR]

Multi-reference configuration interaction potential energy curves (PECs) and spin–orbit couplings for the X 2Π, A 2Σ+, 1 2Σ−, 1 4Σ−, and 1 4Π states of OH are computed and refined against empirical energy levels and transitions to produce a spectroscopic model. Predissociation lifetimes are determined by discretizing continuum states in the variational method nuclear motion calculation by restricting the calculation to a finite range of internuclear separations. Varying this range gives a series of avoided crossings between quasi-bound states associated with the A 2Σ+ and continuum states, from which predissociation lifetimes are extracted. 424 quasi-bound A 2Σ+ state rovibronic energy levels are analyzed, and 374 predissociation lifetimes are produced, offering good coverage of the predissociation region. Agreement with measured lifetimes is satisfactory, and a majority of computed results were within experimental uncertainty. A previously unreported A 2Σ+ state predissociation channel that goes via X 2Π is identified in the calculations. A Python package, binSLT, produced to calculate predissociation lifetimes, associated line broadening parameters, and lifetime uncertainties is made available. The PECs and other curves from this work will be used to produce a rovibronic ExoMol line list and temperature-dependent photodissociation cross sections for the hydroxyl radical. [ABSTRACT FROM AUTHOR]

The largest ever set, RotGT-2023, of statistically validated experimental components of rotational g tensors and respective vibrational corrections, has been created. The experimental values were collected from literature data. The vibrational corrections for obtaining equilibrium molecular g values have been calculated at the highest affordable coupled cluster level of theory. The set comprises 278 parameters from 129 molecules, including their isotopologues. Statistical assessment of the data has been performed to exclude unreliable parameters. A benchmarking of two theoretical approximations, based on coupled cluster and density functional theories, has been performed. The determined weighted mean and weighted standard deviations of the relative errors in calculated equilibrium g values are 1.09% and 2.07% for the ae-CCSD(T)/x2c-TZVPPall-s//ae-CCSD(T)/cc-pwCVTZ level. The obtained results can be used for predicting the rotational Zeeman effect, correcting rotational constants in spectroscopic studies and in molecular structure refinements. The latter has been demonstrated on the refinement of the molecular structure of silane SiH4, which resulted in r e se (Si–H) = 1.473 323 1(27) Å. The other tested theoretical protocol, PBE0/x2c-TZVPPall-s//PBE0-D3BJ/def2-QZVPP, showed considerably worse statistical properties. The RotGT-2023 data set and the developed in this work statistical model are recommended for benchmarking of theoretical approximations for calculations of molecular magnetic properties. [ABSTRACT FROM AUTHOR]

Rationale: Cluster forms of rhenium sulfides have important practical applications as catalysts in oil refining and thus present high interest. However, only a limited number of rhenium sulfide clusters have been described previously. It is known that cluster formation actively occurs under conditions of laser desorption–ionization; nevertheless, detailed studies of rhenium sulfides under such conditions were apparently not conducted previously. Methods: A sample of natural rhenium sulfide, collected from the fumarolic field of Kudriavy volcano (Iturup island, Russia) in 2002, was investigated using the laser desorption–ionization mass spectrometry method. The formed rhenium sulfide clusters were registered by a time‐of‐flight detector and identified programmatically using the software developed in IPCE RAS. The identification involved a comparison of the distribution of isotopic peak intensities, observed in the resulting mass spectra, with the theoretical probabilities of occurrence of various isotopologues for hypothetical rhenium sulfide species. Results: Over 60 rhenium sulfide clusters of RexSy+ and RexSyOz− types containing up to 10 rhenium atoms were formed when a sample of natural rhenium sulfide was exposed to laser desorption–ionization conditions. Several isolated heterometallic ReXMoSY+ and ReXMoSYOZ− clusters containing up to eight rhenium atoms were additionally observed in the resulting mass spectra. The species with compositions, for which the electrically neutral analogs are known, apparently were the most stable rhenium sulfide clusters among the detected ones. Conclusions: The obtained data allowed summarizing the patterns of formation of rhenium sulfide clusters under conditions of laser desorption‐ionization. The ability of rhenium and sulfur to form cluster species containing from 7 to 10 atoms of rhenium was likely discovered for the first time. The majority of the rhenium sulfide clusters described in this study, notably RexSy+ ions containing over seven atoms of rhenium, were apparently not observed previously. [ABSTRACT FROM AUTHOR]

Qudits are anticipated to streamline quantum computation by minimizing iterations, lowering error rates, and facilitating error correction. It has been shown that Dy(III)-based molecular systems can act as qudits with expanded Hilbert spaces. Achieving a robust intramolecular interaction, whether exchange or dipolar, is crucial for spanning the Hilbert space of qudits; hence, short Dy(III)⋯Dy(III) distances are required. Looking for multilevel systems that can be employed as qudits, we have synthesized and characterized two dysprosium-based isotopologues: [163Dy2(BTFA)4(PHZP)2]0 (1(I=5/2)) and [164Dy2(BTFA)4(PHZP)2]0 (2(I=0)), where BTFA = 3-benzoyl-1,1,1-trifluoroacetone and PHZP = N′-[(E)-(pyrazin-2-yl)methylidene]pyrazine-2-carbohydrazonate. Both complexes showed slow magnetic relaxation at zero applied magnetic field. μSQUID investigations, at milli-Kelvin temperatures, and direct and alternating current magnetic measurements reveal distinctions in the magnetic behavior between the two complexes and an operative interaction between the Dy(III) centers. We find that the presence or absence of the nuclear spin plays a minor role in the magnetic properties above 2 K. On the contrary, at milli-Kelvin temperatures, μSQUID studies show enhanced relaxation in 1(I=5/2), attributed to several quantum tunnelling pathways enabled by hyperfine and quadrupole interactions. The interplay between the antiferromagnetic coupling and enhanced relaxation indicates that the exchange coupling influences the relaxation mechanisms at different temperature ranges. [ABSTRACT FROM AUTHOR]

Context. IRAS 16293E is a rare case of a prestellar core being subjected to the effects of at least one outflow. Aims. We want to disentangle the actual structure of the core from the outflow impact and evaluate the evolutionary stage of the core. Methods. Prestellar cores being cold and depleted, the best tracers of their central regions are the two isotopologues of the trihydrogen cation that are observable from the ground: ortho-H2D+ and para-D2H+. We used the Atacama Pathfinder EXperiment (APEX) telescope to map the para-D2H+ emission in IRAS 16293E and collected James Clerk Maxwell Telescope (JCMT) archival data of ortho-H2D+. We compared their emission to that of other tracers, including dust emission, and analysed their abundance with the help of a 1D radiative transfer tool. The ratio of the abundances of ortho-H2D+ to para-D2H+ can be used to estimate the stage of the chemical evolution of the core. Results. We have obtained the first complete map of para-D2H+ emission in a prestellar core. We compare it to a map of ortho-H2D+ and show their partial anti-correlation. This reveals a strongly evolved core with a para-D2H+/ortho-H2D+ abundance ratio towards the centre for which we obtain a conservative lower limit from 3.9 (at 12 K) to 8.3 (at 8 K), while the high extinction of the core is indicative of a central temperature below 10 K. This ratio is higher than predicted by the known chemical models found in the literature. Para-D2H+ (and indirectly ortho-H2D+) is the only species that reveals the true centre of this core, while the emission of other molecular tracers and dust are biased by the temperature structure that results from the impact of the outflow. Conclusions. This study is an invitation to reconsider the analysis of previous observations of this source and possibly questions the validity of the deuteration chemical models or of the reaction and inelastic collisional rate coefficients of the H+3 H 3 + isotopologue family. This could impact the deuteration clock predictions for all sources. [ABSTRACT FROM AUTHOR]

The features of the infrared (IR) spectra of various isotopic forms of water (–OH, –OD, H2O, HDO, and D2O) included in the crystal structure of the main rock-forming minerals of lunar basalts—olivines (forsterite)—have been studied. The results of numerical modeling (CUSTEP/Biovia Materials Studio) and experimental studies using the FT-801 IR Fourier spectrometer with a plug-in using the method of disturbed internal reflection (Simex, Novosibirsk) are presented. Numerical calculations have shown that forsterite can contain hydroxyl groups –OH(D) in its crystal lattice under certain conditions. The possibility of retaining various isotopic forms of molecular water on the surface of forsterite has been experimentally verified and the corresponding IR spectra of the mineral with a water film have been obtained. The IR spectra of forsterite containing isotopologues of water obtained theoretically and experimentally are compared with the observations of the Chandrayaan-1 and SOFIA artificial lunar satellites. [ABSTRACT FROM AUTHOR]

The absorption spectrum of H219O, a radioactive isotopologue of the water molecule, is predicted using variational nuclear motion calculated based on a high precision potential energy function and ab initio dipole moment surface. Vibrational - rotational energy levels and wave functions, line centers and Einstein coefficients for dipole transitions are calculated. Predicted transition wavenumbers are improved by extrapolating known empirical energy levels of the stable H216O, H217O and H218O isotopologues to H219O. A line list for possible atmospheric application is presented which includes air line broadening coefficients. The calculations span a wide spectral range covering infrared and visible wavelengths, and are appropriate for temperatures up to 1000 K. Windows suitable for observing absorption by H219O are identified and comparisons made with the infrared spectra of water vapor in natural abundance, H215O and H214O. [ABSTRACT FROM AUTHOR]

Methods are lacking that can prepare deuterium-enriched building blocks, in the full range of deuterium substitution patterns at the isotopic purity levels demanded by pharmaceutical use. To that end, this work explores the regio- and stereoselective deuteration of tetrahydropyridine (THP), which is an attractive target for study due to the wide prevalence of piperidines in drugs. A series of d0–d8 tetrahydropyridine isotopomers were synthesized by the stepwise treatment of a tungsten-complexed pyridinium salt with H−/D− and H+/D+. The resulting decomplexed THP isotopomers and isotopologues were analyzed via molecular rotational resonance (MRR) spectroscopy, a highly sensitive technique that distinguishes isotopomers and isotopologues by their unique moments of inertia. In order to demonstrate the medicinal relevance of this approach, eight unique deuterated isotopologues of erythro-methylphenidate were also prepared. Deuteration of active pharmaceutical ingredients is increasingly applied as the isosteric and isotopic replacement can modulate the pharmacokinetic profile, without necessarily having to alter the overall synthetic strategy toward the compound of interest. Here, the authors show manifold deuterations of piperidines and apply molecular rotational resonance (MRR) spectroscopy as a methodology to distinguish isotopomers within a distribution of products. [ABSTRACT FROM AUTHOR]

The millimeter-wave rotational spectrum of ketene (H2C=C=O) has been collected and analyzed from 130 to 750 GHz, providing highly precise spectroscopic constants from a sextic, S-reduced Hamiltonian in the Ir representation. The chemical synthesis of deuteriated samples allowed spectroscopic measurements of five previously unstudied ketene isotopologues. Combined with previous work, these data provide a new, highly precise, and accurate semi-experimental (reSE) structure for ketene from 32 independent moments of inertia. This reSE structure was determined with the experimental rotational constants of each available isotopologue, together with computed vibration–rotation interaction and electron-mass distribution corrections from coupled-cluster calculations with single, double, and perturbative triple excitations [CCSD(T)/cc-pCVTZ]. The 2σ uncertainties of the reSE parameters are ≤0.0007 Å and 0.014° for the bond distances and angle, respectively. Only S-reduced spectroscopic constants were used in the structure determination due to a breakdown in the A-reduction of the Hamiltonian for the highly prolate ketene species. All four reSE structural parameters agree with the "best theoretical estimate" (BTE) values, which are derived from a high-level computed re structure [CCSD(T)/cc-pCV6Z] with corrections for the use of a finite basis set, the incomplete treatment of electron correlation, relativistic effects, and the diagonal Born–Oppenheimer breakdown. In each case, the computed value of the geometric parameter lies within the statistical experimental uncertainty (2σ) of the corresponding semi-experimental coordinate. The discrepancies between the BTE structure and the reSE structure are 0.0003, 0.0000, and 0.0004 Å for rC–C, rC–H, and rC–O, respectively, and 0.009° for θC–C–H. [ABSTRACT FROM AUTHOR]

The gas-phase rotational spectra of α-pinene oxide have been recorded using a chirped-pulse Fourier transform microwave spectrometer in the 6–18 GHz frequency range. The parent species and all heavy atom isotopologues (13C and 18O) have been observed in their natural abundance. The experimental rotational constants of all isotopic species observed have been determined and used to obtain the substitution (rs) and the effective (r0) structures of the most stable conformer of α-pinene oxide. Calculations using the density functional theories B3LYP, M06-2X, and MN15-L and the ab initio method MP2 level of theory were carried out to check their performance against experimental results. The structure of the heavy atom's skeleton of α-pinene oxide has been compared to that of α-pinene and has shown that epoxidation does not overly affect the structure of the bicycle, validating its robustness. Furthermore, the structural features have been compared to those of other bicyclic molecules, such as nopinone and β-pinene. [ABSTRACT FROM AUTHOR]

Aerobic methane oxidation (AeOM) is an important biological sink of methane on Earth. Stable isotopes are critical tools in tracking the sources and sinks of Earth's surface methane budget. However, the major factors that influence the two multiply-substituted (clumped) isotope signatures of AeOM, Δ 13 CH 3 D and Δ 12 CH 2 D 2 , are not well known. Here we quantify the influence of kinetics as a function of temperature and different methane monooxygenase (MMO) enzymes (modulated by copper) on the isotopologue concentrations of residual methane by the obligate aerobic methanotroph, Methylococcus capsulatus (Bath). We observe deviations from traditional closed-system distillation (Rayleigh) fractionation during exponential growth at high oxidation rates. We model this as a reservoir effect controlled by the ratio of oxidation rate in the cells to transport rate of methane into the cells, where environmental temperature affects both rates. We also test whether clumped isotope fractionation values vary for the particulate versus soluble MMOs, but the results show minimal differences. We further determine that the back reaction (re-equilibration) of methane with medium water is unlikely. Together, the observations and model demonstrate that at low oxidation-to-transport ratios, the clumped isotope signatures follow canonical Rayleigh fractionation, whereas at high ratios, more positive Δ 12 CH 2 D 2 values result, deviating from simple Rayleigh-like trajectories. This study shows that the methane oxidation-to-transport ratio is a critical influence on clumped isotope signatures of AeOM that should be considered when interpreting the isotopic data of natural methane samples in both open and closed systems. [ABSTRACT FROM AUTHOR]

The potential performance of porous membranes in separating hydrogen isotopologues has been explored employing model systems and quanto-mechanical calculations including both zero-point energy and a numerically exact description of tunneling effects along the reaction coordinate. Membranes have been modeled as cylindrically pierced impenetrable wall, whereas diatomic molecules are described as dumbells composed of hard-sphere atoms. With the relative energetics of diatomics confined into cylindrical pores suggesting that differences in the adiabatic energy profiles between isotopologues for pore radii lower than 2.1 Å should favor transport of heavier species, we investigated the selectivity for the latter process when membranes are 2.0 Å thick. Chosen a pore radius, the results suggest that non-interacting pores represent the best compromise between selectivity and permeance, the addition of attraction between the membrane walls and molecular projectiles improving permeance while markedly depressing selectivity. A repulsive interaction with the pore inner surface, instead, reduced both properties. Finally, sieving molecules through a double membrane layer was found to marginally impact on the separation properties, which could be improved, at best, by 25% with a careful selection of the inter-membrane distance. Our results appear useful for the process of designing more effective sieving systems to separate di-deuterium molecules from its lighter counterparts. [Display omitted] • Determine the quantum energetics of H 2 and D 2 inside cylindrical channels including rotations. • Explore the effect of membrane pore radius on the transmission probability. • Investigating dependence of permeance and D 2 /H 2 selectivity on the molecule/pore interaction modalities. • Defining the impact of sieving H 2 and D 2 through two membranes as a function of their distance. [ABSTRACT FROM AUTHOR]

The total internal partition sum, Qint(T), and the translational partition sum, Qtrans(T), were computed for six isotopologues of NO: 14N16O, 15N16O, 14N18O, 14N17O, 15N18O, 15N17O. These were used to determine the total partition sum, Q(T), and its first and second moments, Q ̃ ′ T and Q ̃ ″ T . The total internal partition sum was computed using term values determined by Qu et al. [Mon. Not. R. Astron. Soc. 504, 5768–5777 (2021)] for 14N16O and those of Wong et al. [Mon. Not. R. Astron. Soc. 470, 882–897, (2017)] for the other isotopologues. These term values are the best available and hence provide the most accurate total internal partition sums and its first and second moments. The uncertainties in Qint(T), its moments, and the resulting thermodynamic functions were determined from the uncertainty in the term values and the uncertainty due to the convergence of the partition sum and its moments. From these quantities, the isobaric heat capacity, Helmholtz energy, entropy, enthalpy, Gibbs function, and the JANAF functions hef and gef, and their uncertainties, were computed on a 1 K grid from 1 to 9000 K. The data are compared with the literature values. The resulting thermodynamic quantities are the most accurate determined from direct summation of Q(T), Q ̃ ′ T , and Q ̃ ″ T . [ABSTRACT FROM AUTHOR]

Rationale: Dual clumped isotope paleothermometry determines carbonate formation temperatures by measuring the frequency of 13C–18O (∆638) and 18O–18O (∆828) pairs in carbonates. It resolves isotopic kinetic biases and thus enables more accurate paleotemperature reconstructions. However, high‐precision measurements of 18O–18O clumping using current techniques requires large sample sizes and long acquisition times. Methods: We developed a mid‐infrared isotope ratio laser spectrometer (IRLS) for simultaneous measurement of the isotopologue ratios ∆638 and ∆828 in gas‐phase carbon dioxide (CO2) at room temperature. Our IRLS uses a single laser scanning from 2290.7 to 2291.1 cm−1 and a 31 m pathlength optical cell, and it simultaneously measures the five isotopologues required for calculating ∆638 and ∆828: 16O12C16O, 16O13C16O, 16O12C18O, 16O13C18O, and 18O12C18O. In addition, our IRLS can measure 16O12C17O, enabling ∆17O analysis. Results: At ~20°C and a CO2 pressure of ~2 Torr, our IRLS system achieved precisions of 0.128‰ and 0.140‰ within 20 s for abundances of the clumped isotopologues 16O13C18O and 18O12C18O, respectively, and precisions of 0.267‰, 0.245‰, and 0.128‰ for 16O12C16O, 16O13C16O, and 16O12C18O. This yielded precisions of 0.348‰ (∆638) and 0.302‰ (∆828) within 25 s. Simulated sample–reference switching highlights the potential of our system and the need for further development. Conclusions: We demonstrated simultaneous measurements of ∆638 and ∆828 in CO2 to precisions of <0.35‰ within 25 s using a room‐temperature, single‐laser IRLS. Future developments on better resolving 16O12C16O and 16O13C16O peaks and system temperature control could further improve the measurement precision. [ABSTRACT FROM AUTHOR]

Rationale: Dual clumped isotope paleothermometry determines carbonate formation temperatures by measuring the frequency of 13C–18O (∆638) and 18O–18O (∆828) pairs in carbonates. It resolves isotopic kinetic biases and thus enables more accurate paleotemperature reconstructions. However, high‐precision measurements of 18O–18O clumping using current techniques requires large sample sizes and long acquisition times. Methods: We developed a mid‐infrared isotope ratio laser spectrometer (IRLS) for simultaneous measurement of the isotopologue ratios ∆638 and ∆828 in gas‐phase carbon dioxide (CO2) at room temperature. Our IRLS uses a single laser scanning from 2290.7 to 2291.1 cm−1 and a 31 m pathlength optical cell, and it simultaneously measures the five isotopologues required for calculating ∆638 and ∆828: 16O12C16O, 16O13C16O, 16O12C18O, 16O13C18O, and 18O12C18O. In addition, our IRLS can measure 16O12C17O, enabling ∆17O analysis. Results: At ~20°C and a CO2 pressure of ~2 Torr, our IRLS system achieved precisions of 0.128‰ and 0.140‰ within 20 s for abundances of the clumped isotopologues 16O13C18O and 18O12C18O, respectively, and precisions of 0.267‰, 0.245‰, and 0.128‰ for 16O12C16O, 16O13C16O, and 16O12C18O. This yielded precisions of 0.348‰ (∆638) and 0.302‰ (∆828) within 25 s. Simulated sample–reference switching highlights the potential of our system and the need for further development. Conclusions: We demonstrated simultaneous measurements of ∆638 and ∆828 in CO2 to precisions of <0.35‰ within 25 s using a room‐temperature, single‐laser IRLS. Future developments on better resolving 16O12C16O and 16O13C16O peaks and system temperature control could further improve the measurement precision. [ABSTRACT FROM AUTHOR]

The predicted rotation-vibration absorption spectrum of the radioactive isotopically substituted water molecule, H214O, is presented. Variational nuclear-motion calculations are performed using the DVR3D software package based on the use of a high-precision potential energy function and an accurate dipole moment surface. Line centres, intensity and Einstein coefficients are calculated, and air pressure broadening coefficients are estimated. The calculation was carried out over a wide wavenumber range from 0 to 25000 cm $ {}^{-1} $ − 1 and total angular momentum up to J = 20. Isotopologue extrapolation rules based on experimental data on the energy levels of the stable isotopologues H216O, H $ {}_{2}^{16} $ 2 16 O H217O and H218O were also used to improve the predicted line positions. Spectral ranges best suited to the detection of H214O are identified. [ABSTRACT FROM AUTHOR]

Thioformyl cyanide, HC(S)CN, and its deuterated isotopologue have been studied by high-level ab initio methods. Based on multidimensional potential energy surfaces including up to four-mode coupling terms and obtained from explicitly correlated coupled-cluster calculations, their geometrical parameters, vibrational transitions, rovibrational spectrum and spectroscopic constants have been studied in detail. The latter two properties, being obtained from vibrational configuration interaction theory (VCI) and vibrational perturbation theory (VPT), have been compared with available experimental data. The rotational and rovibrational spectra have been studied by rovibrational configuration interaction theory (RVCI) and colour coding has been used to obtain detailed insight into the rotational fine structure. [ABSTRACT FROM AUTHOR]

In contrast to the traditional analysis of molecules using local mode behavior, where the degree of locality is given through a function in terms of Morse potential parameters, new criteria for locality/normality (LN) suitable for application to any molecular system are proposed. The approach is based on analysis of the connection between the algebraic normal and local mode representations. It is shown that both descriptions are equivalent as long as the polyad (total number of quanta) in the local representation is not conserved. The constraint of a local polyad conservation naturally provides a criterion for assigning an LN degree in quantitative form, without an analogue in configuration space. The correlation between the different parameters reveals the physical properties of molecules. A clear connection between the LN degree (based on the fundamentals) and spectroscopic properties is also presented, suggesting a promising approach for identifying mixtures of isotopologues. [ABSTRACT FROM AUTHOR]

We performed correlation analyses between the 12CO and 13CO J = 1–0 line intensities in order to derive the variability of the CO-to-H2 conversion factor (X CO,iso) in the central molecular zone (CMZ) of our Galaxy. New high-resolution X CO,iso maps at a resolution of ∼30″ and a longitude–velocity diagram (LVD) at resolution |${\sim }{30^{\prime\prime}}\times 2$| km s−1 are presented using the 12CO and 13CO archival survey data obtained by the Nobeyama 45 m telescope. We revealed the variation of X CO,iso in the CMZ within the range of X CO,iso ∼ (0.2–1.3) × 1020 cm−2 (K km s−1)−1, if we assume a normalization value of 0.59 × 1020 cm−2 (K km s−1)−1. The mean value is obtained as X CO,iso = (0.48 ± 0.15) × 1020 cm−2 (K km s−1)−1 in the CMZ of our Galaxy. [ABSTRACT FROM AUTHOR]

Episodic accretion in protostars leads to luminosity outbursts that end up heating their surroundings. This rise in temperature pushes the snow lines back, enabling the desorption of chemical species from dust grain surfaces, which may significantly alter the chemical history of the accreting envelope. However, a limited number of extensive chemical surveys of eruptive young stars have been performed thus far. In the present study, we carry out a large spectral survey of the binary Class I protostar L1551 IRS 5, known to be a FUor-like object, in the 3 mm and 2mm bands with the IRAM-30m telescope. As a result, we detected more than 400 molecular lines. The source displays a great chemical richness with the detection of 75 species, including isotopologues. Among these species, there are 13 hydrocarbons, 25 N-bearing species, 30 O-bearing species, 15 S-bearing species, 12 deuterated molecules, and a total of 10 complex organic molecules (l-C4H2, CH3CCH, CH2DCCH, CH3CHO, CH3CN, CH3OCH3, CH3OCHO, CH3OH, CH2DOH, and HC5N). With the help of local thermodynamic equilibrium (LTE) and non-LTE models, we determined the column densities of most molecules as well as excitation and kinetic temperatures. While most of those molecules trace the cold envelope (≲20 K), the OCS and CH3OH emission arise from the warm (>100 K) innermost (<2″) regions. We compared the chemical inventory of L1551 IRS 5 and its column density ratios, including isotopic ratios, with other protostellar sources. A broad chemical diversity is seen among Class I objects. More observations with both single-dish telescopes and interferometers are needed to characterize the diversity in a larger sample of protostars, while more astrochemical models would help explain this diversity, in addition to the impact of luminosity outbursts on the chemistry of protostellar envelopes. [ABSTRACT FROM AUTHOR]

We present synthetic line observations of a simulated molecular cloud, utilizing a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues (12CO, 13CO, C18O) and six supposed tracers of dense gas (NH3, HCN, N2H+, HCO+, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N2H+ to HCN or CO, on the other hand, is highly selective of regions with densities above |$10^{22} \, {\rm cm}^{-2}$|⁠ , and the N2H+ line is a very good tracer of the dynamics of high volume density (⁠|$\gt 10^4 \, {\rm cm}^{-3}$|⁠) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data. [ABSTRACT FROM AUTHOR]

The 2,2,2-trifluoroethoxy group increasingly features in drugs and potential tracers for biomedical imaging with positron emission tomography (PET). Herein, we describe a rapid and transition metal-free conversion of fluoroform with paraformaldehyde into highly reactive potassium 2,2,2-trifluoroethoxide (CF3CH2OK) and demonstrate robust applications of this synthon in one-pot, two-stage 2,2,2-trifluoroethoxylations of both aromatic and aliphatic precursors. Moreover, we show that these transformations translate easily to fluoroform that has been labeled with either carbon-11 (t1/2 = 20.4 min) or fluorine-18 (t1/2 = 109.8 min), so allowing the appendage of complex molecules with a no-carrier-added 11C- or 18F- 2,2,2-trifluoroethoxy group. This provides scope to create candidate PET tracers with radioactive and metabolically stable 2,2,2-trifluoroethoxy moieties. We also exemplify syntheses of isotopologues of potassium 2,2,2-trifluoroethoxide and show their utility for stable isotopic labeling which can be of further benefit for drug discovery and development. The 2,2,2-trifluoroethoxy group features in drugs and potential tracers for biomedical imaging with positron emission tomography. Herein, the authors report the conversion of fluoroform into potassium 2,2,2-trifluoroethoxide isotopologues and their applications in late stage 2,2,2-trifluoroethoxylations of aromatic and aliphatic substrates for positron emission tomography and stable isotope labeling. [ABSTRACT FROM AUTHOR]

The thermodynamic and transport properties of hydrogen isotopologues in the solid, liquid, and gas phases are crucial for hydrogen energy exploitation, such as the design of the fuel cycle of nuclear fusion reactors. However, experimental data for tritium-containing species are often not available. Alternatively, path integral (PI) simulation can evaluate hydrogen properties taking into account nuclear quantum effects; however, concerns about its reliability are present. This study proposes a method of Gaussian process regression (GPR) using both experimental and PI simulation data to obtain practically plausible estimates for all isotopologues. Using liquid viscosity and diffusivity as test cases, we demonstrate that the present method has high and robust predictive performance. The method has broad applicability and can also be used to design experiments and calculations to efficiently improve the regression model, and thus is expected to contribute to enhancing the availability and reliability of the hydrogen isotopologue property database. [Display omitted] • Experimental data on hydrogen properties are scarce for tritium-containing species. • Reliability of path-integral simulations is still limited. • Gaussian process regression can yield plausible predictions for all isotopologues. • The regression model can be efficiently improved using estimated model uncertainty. [ABSTRACT FROM AUTHOR]

Imidogen (NH) is a reactive molecule whose presence in astrochemical environments is of interest due to its role in the formation of nitrogen-containing molecules and as a potential probe of nitrogen abundance. Spectroscopic NH monitoring is useful for Earth-based combustion and photolysis processes of ammonia and other nitrogen-containing species. NH is also relevant to ultracold molecular physics and plasma studies. To enable these diverse applications, high-quality molecular spectroscopic data are required. Here, a new line list with significant advantages over existing data is presented. Most notably, this line list models isotopologue spectroscopy and forbidden transitions (important for NH visible absorption), alongside some overall improvements to accuracy and completeness. This approach takes advantage of existing experimental data (from a previous MARVEL compilation) and perturbative line lists together with new MRCI ab initio electronic data. These are used to produce a novel variational spectroscopic model and trihybrid line list for the main 14N1H isotopologue, as well as isotopologue-extrapolated hybrid line lists for the 14N2H, 15N1H, and 15N2H isotopologues. The new 14N1H ExoMol-style trihybrid line list, kNigHt , comprises 4076 energy levels (1078 experimental) and 327 014 transitions up to 47 500 cm−1 (211 nm) between five low-lying electronic states (X 3Σ−, a 1Δ, b 1Σ+, A 3Π, and c 1Π). For most anticipated applications aside from far-infrared studies, this line list will be of sufficient quality; any improvements should focus on the b 1Σ+ energies, and the a 1Δ – A 3Π and b 1Σ+ – A 3Π spin–orbit couplings. [ABSTRACT FROM AUTHOR]

In this work, we present the spectral analysis of 1H- and 2H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1H-1,2,3-triazole and five of its deuteriated isotopologues ([1-2H]-, [4-2H]-, [5-2H]-, [4,5-2H]-, and [1,4,5-2H]-1H-1,2,3-triazole), as well as those of 2H-1,2,3-triazole and five of its deuteriated isotopologues ([2-2H]-, [4-2H]-, [2,4-2H]-, [4,5-2H]-, and [2,4,5-2H]-2H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130–375 GHz frequency region. The normal and [2-2H]-isotopologues of 2H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration–rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500 kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied. [ABSTRACT FROM AUTHOR]

4-aminobenzoic acid (4ABA) is a model scaffold for studying solvent-mediated proton transfer. Although protonation at the carboxylic group (O-protomer) is energetically favored in the gas phase, the N-protomer, where the proton remains on the amino group, can be kinetically trapped by electrospray ionization of 4ABA in an aprotic solvent such as acetonitrile. Here, we report the formation of the hydrated deuterium isotopologues of the N-protomers, RND3+·(H2O)n=1–3, (R = C6H4COOD), which are generated by condensing water molecules onto the bare N-protomers in a liquid nitrogen cooled, radiofrequency octopole ion trap at 80 K. The product clusters are then transferred to a 20 K cryogenic ion trap where they are tagged with weakly bound D2 molecules. The structures of these clusters are determined by analysis of their vibrational patterns, obtained by resonant IR photodissociation. The resulting patterns confirm that the metastable N-protomer configuration remains intact even when warmed by the sequential condensation of water molecules. The attachment of H2O molecules onto the RND3+ head group also affords the opportunity to explore the possibility of H/D exchange between the acid scaffold and the proximal water network. The spectroscopic results establish that although the RND3+·(H2O)n=1,2 clusters are formed without H/D exchange, the n = 3 cluster exhibits about 10% H/D exchange as evidenced by the appearance of the telltale HOD bands. The site of exchange on the acid is determined to be the acidic OH group by the emergence of the OH stretching fundamental in the –COOH motif. [ABSTRACT FROM AUTHOR]

During D-T fusion operations the capture, purification, and recycling of unburned tritium will be crucial, as the formation of tritium containing molecules require additional processing. Removing the tritium can require costly processing to be unbound from the tritium-containing molecules and improvements to these processes will be necessary moving forward. Existing techniques using sorbent material beds to remove tritium-containing molecules from process gas streams undergo repeated high-heat cycling which leads to diminished bed lifespans, necessitating replacement and associated downtime. This work demonstrates the capture and isotopic exchange technique of deuterated ammonia (ND 3), used as a surrogate for tritium, at ambient temperature using a Pt catalyst-loaded 13X molecular sieve. Unmodified 13X molecular sieve is capable of adsorbing and retaining the ND 3 however, incorporation of a catalyst facilitates the isotopic exchange of the hydrogen isotopes. The effluent gas streams were analyzed in conjunction with desorbed ammonia isotopologues post-exchange to verify these results. Isotopically exchanging and removing heavier hydrogen isotopes using this technique provides an alternative to traditional removal methods. • Hydrogen isotopes successfully exchanged at ambient temperature with Pt catalyst present on support material. • Pt-loaded 13X demonstrates higher capacity for ND 3 when compared to 13X • Pt-loaded 13X requires lower temperatures for full desorption of ND 3 when compared to 13X [ABSTRACT FROM AUTHOR]

Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. We reveal the commensurate locking of a SkL to the atomic lattice in Gd3Ru4Al12 via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures – but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, and the role of slight discommensurations, or (line) defects in the magnetic texture. We also contrast our findings with the case of SkLs in noncentrosymmetric material platforms. [ABSTRACT FROM AUTHOR]

This work presents a proposed extension to the International Union of Pure and Applied Chemistry (IUPAC) International Chemical Identifier (InChI) standard that allows the representation of isotopically-resolved chemical entities at varying levels of ambiguity in isotope location. This extension includes an improved interpretation of the current isotopic layer within the InChI standard and a new isotopologue layer specification for representing chemical intensities with ambiguous isotope localization. Both improvements support the unique isotopically-resolved chemical identification of features detected and measured in analytical instrumentation, specifically nuclear magnetic resonance and mass spectrometry. Scientific contribution: This new extension to the InChI standard would enable improved annotation of analytical datasets characterizing chemical entities, supporting the FAIR (Findable, Accessible, Interoperable, and Reusable) guiding principles of data stewardship for chemical datasets, ultimately promoting Open Science in chemistry. [ABSTRACT FROM AUTHOR]

Context. The physics and chemistry of planet-forming disks are far from being fully understood. To make further progress, both broad line surveys and observations of individual tracers in a statistically significant number of disks are required. Aims. Our aim is to perform a line survey of eight planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning). Methods. Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ~80 lines from > 20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210–280 GHz with a 1σ rms sensitivity of ~8–12 mJy beam−1 at a 0.9″ and 0.3 km s−1 resolution will be completed in 2024. The uv visibilities are fitted with the DiskFit model to obtain key stellar and disk properties. Results. In this first paper, the combined 12CO, 13CO, and C18O J = 2–1 data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrained dynamical stellar masses, geometries, temperatures, the CO column densities, and gas masses for each disk. The best-fit temperatures at 100 au are ~ 17–37 K, and decrease radially with the power-law exponent q ~ 0.05–0.76. The inferred CO column densities decrease radially with the power-law exponent p ~ 0.2–3.1. The gas masses estimated from 13CO (2–1) are ~0.001–0.2 M⊙. Conclusions. Using NOEMA, we confirm the presence of temperature gradients in our disk sample. The best-fit CO column densities point to severe CO freeze-out in these disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions. The high 13CO/C18O ratio of ~23 in DM Tau could be indicative of strong selective photodissociation of C18O in this disk. [ABSTRACT FROM AUTHOR]

The isotopically independent parameters Umj, , and of the HBr molecule were determined based on the analysis of the experimental frequencies of transitions of six isotopic modifications. The resulting values were used to calculate both the vibrational-rotational energies and transition frequencies up to the vibrational state v = 8 and the RKR potentials of six isotopologues. The calculated transition frequencies were compared with data from the HITRAN database. [ABSTRACT FROM AUTHOR]

Detection sensitivity is a critical characteristic to consider during selection of spectroscopic techniques. However, high sensitivity alone is insufficient for spectroscopic measurements in spectrally congested regions. Two-color cavity ringdown spectroscopy (2C-CRDS), based on intra-cavity pump-probe detection, simultaneously achieves high detection sensitivity and selectivity. This combination enables mid-infrared detection of radiocarbon dioxide (14CO2) molecules in room-temperature CO2 samples, with 1.4 parts-per-quadrillion (ppq, 10-15) sensitivity (average measurement precision) and 4.6-ppq quantitation accuracy (average calibrated measurement error for 21 samples from four separate trials) demonstrated on samples with 14C/C up to ~1.5× natural abundance (~1,800 ppq). These highly reproducible measurements, which are the most sensitive and quantitatively accurate in the mid-infrared, are accomplished despite the presence of orders-of-magnitude stronger, one-photon signals from other CO2 isotopologues. This is a major achievement in laser spectroscopy. A room-temperature-operated, compact, and low-cost 2C-CRDS sensor for 14CO2 benefits a wide range of scientific fields that utilize 14C for dating and isotope tracing, most notably atmospheric 14CO2 monitoring to track CO2 emissions from fossil fuels. The 2C-CRDS technique significantly enhances the general utility of high-resolution mid-infrared detection for analytical measurements and fundamental chemical dynamics studies. [ABSTRACT FROM AUTHOR]

We present mass‐correlated rotational alignment spectroscopy and the first high‐resolution rotational Raman spectra for furan. Spectra were measured with a spectral range up to 0.5 THz and a resolution down to 1.6 MHz. Spectra for 13C and 18O isotopologues were observed in their corresponding mass channels at natural abundance. Based on our data and literature constants, we performed a purely experimental structure analysis for the effective and equilibrium structures of furan. The results highlight the utility of CRASY to obtain rare isotopologue spectra without isotopically enriched samples. [ABSTRACT FROM AUTHOR]

We present a study of salicylic acid and its hydrates, with up to four water molecules, done by employing chirped-pulse Fourier transform microwave spectroscopy. We employed the spectral data set of the parent, 13C, and 2H isotopologues to determine the molecular structure and characterize the intra- and intermolecular interactions of salicylic acid and its monohydrate. Complementary theoretical calculations were done to support the analysis of the experimental results. For the monomer, we analyzed structural properties, such as the angular-group-induced bond alternation (AGIBA) effect. In the microsolvates, we analyzed their main structural features dominated by the interaction of water with the carboxylic acid group. This work contributes to seeding information on how water molecules accumulate around this group. Moreover, we discussed the role of cooperative effects further stabilizing the observed inter- and intramolecular hydrogen bond interactions. [ABSTRACT FROM AUTHOR]

An investigation of the rotational spectrum of the interstellar molecule thioformaldehyde between 110 and 377 GHz through a pyrolysis reaction revealed a multitude of absorption lines assignable to H $ _2 $ 2 CS and H $ _2 $ 2 C $ ^{34} $ 34 S in their lowest four excited vibrational states besides lines of numerous thioformaldehyde isotopologues in their ground vibrational states reported earlier as well as lines pertaining to several by-products. Additional transitions of H $ _2 $ 2 CS in its lowest four excited vibrational states were recorded in selected regions between 571 and 1386 GHz. Slight to strong Coriolis interactions occur between all four vibrational states with the exception of the two highest lying states because both are totally symmetric vibrations. We present combined analyses of the ground and the four interacting states for our rotational data of H $ _2 $ 2 CS and H $ _2 $ 2 C $ ^{34} $ 34 S. The H $ _2 $ 2 CS data were supplemented with two sets of high-resolution IR data in two separate analyses. The $ v_2 = 1 $ v 2 = 1 state has been included in analyses of Coriolis interactions of low-lying fundamental states of H $ _2 $ 2 CS for the first time and this improved the quality of the fits substantially. We extended furthermore assignments in J of transition frequencies of thioketene in its ground vibrational state. [ABSTRACT FROM AUTHOR]

To facilitate the data analysis of current and future high-resolution space telescope missions, we adopt 'Best Theory + Reliable High-resolution Experiment' (BTRHE) strategy to develop highly accurate infrared line lists for nitrous oxide (N2O). The 'Ames-1' potential energy surface (PES) is a CCSD(T)/aug-cc-pVQZ PES refined using selected HITRAN experimental data, with σrms = 0.02–0.03 cm-1 for five isotopologues. The 'Ames-1' dipole moment surface (DMS) is fitted from CCSD(T)/aug-cc-pV(T,Q,5)Z dipoles extrapolated to one electron basis set limit. Using the Ames-1 PES and DMS, Ames-296K line lists are computed in the full range of 0–15,000 cm-1 for 12 N2O isotopologues, with S296K ≥ 10−31 cm-1/molecule.cm-2. The reliability and consistency of Ames-296K intensity predictions (SAmes) are demonstrated through comparisons with HITRAN (SHITRAN), NOSL-296 (SNOSL), recent observed intensities (Sobs) and Effective Dipole Model (EDM) intensities (SEDM). Agreements and discrepancies are discussed, along with preliminary uncertainty estimate for SAmes. The SAmes provides a good constraint to prevent substantial errors in intensity predictions (e.g. for weak bands and minor isotopologues) and can be further improved. Ames-296K and NOSL-296 may complement each other to provide improved input for future database updates, combining the strengths of EH/EDM and BTRHE approaches. Data available at and https://doi.org/10.48667/9kmk-0334. [ABSTRACT FROM AUTHOR]

We present here the results of the spectroscopic analysis of the high-resolution visible spectra of beryllium hydride and its isotopologues (BeH, BeD, and BeT), produced during plasma–surface interactions during limiter and divertor JET-ILW (ITER-like Wall) pulses. The hydride production, being an important part of the wall erosion via chemical-assisted physical sputtering, shows visible dependence on plasma and wall conditions, and also on the isotope content of the plasma. This work shows that this dependence is also true for the molecular energy distributions, parameterized by rotational and vibrational temperatures. During the increase in the vessel wall temperature by 350 K, with constant plasma parameters, rotational temperature of the excited BeD molecules increases by 500 K, whereas the vibrational temperature decreases by 400 K. Another experiment was the scan of the integrated edge density, during which electron density increases with the increasing edge density, and electron temperature decreases. During that scan for BeD, T rot decreases by 300 K and T vib by 400 K over the change in an integrated edge density of Δ N e = + 8 × 10 18 m − 2 . Both trends were compared with the trends in other isotopes, and the qualitative results are similar, but the limited data available restrict the possibility of a full quantitative comparison. To simplify the comparison between the results presented here and other experiments or modeling data, and also to check the comparability of the pulses performed in different isotopes, the Be ion line ratios are used as benchmarks of the edge plasma condition. [ABSTRACT FROM AUTHOR]

Water stable isotopologue analysis is widely used to disentangle ecohydrological processes. Yet, there are increasing reports of measurement uncertainties for established and emerging methods, such as cryogenic vacuum extraction (CVE) or cavity ring‐down spectroscopy (CRDS). With this study, we investigate two pitfalls, that potentially contribute to uncertainties in water‐stable isotopologue research. To investigate fractionation sources in CVE, we extracted pure water of known isotopic composition with cotton, glass wool or without cover and compared the isotopologue results with non‐extracted reference samples. To characterise the dependency of δ2H and δ18O on the water mixing ratio in CRDS, which is of high importance for in‐situ applications with large natural variations in mixing ratios, we chose samples with a large range of isotopic compositions and determined δ2H and δ18O for different water mixing ratios with two CRDS analysers (Picarro, Inc.). Cotton wool had a strong fractionation effect on δ2H values, which increased with more 2H‐enriched samples. δ2H and δ18O values showed a strong dependency on the water mixing ratio analysed with CRDS with differences of up to 34.5‰ (δ2H) and 3.9‰ (δ18O) for the same sample at different mixing ratios. CVE and CRDS, now routinely applied in water stable isotopologue research, come with pitfalls, namely fractionation effects of cover materials and water mixing ratio dependencies of δ2H and δ18O, which can lead to erroneous isotopologue results and thus, invalid conclusions about (ecohydrological) processes. These practical issues identified here should be reported and addressed adequately in water‐stable isotopologue research. [ABSTRACT FROM AUTHOR]

The intramolecular vibrational relaxation dynamics of formic acid and its deuterated isotopologues is simulated on the full-dimensional potential energy surface of Richter and Carbonnière [J. Chem. Phys. 148, 064303 (2018)] using the Heidelberg MCTDH package. We focus on couplings with the torsion vibrational modes close to the trans–cis isomerization coordinate from the dynamics of artificially excited vibrational mode overtones. The bright C–O stretch vibrational mode is coupled to the out-of-the plane torsion mode in HCOOH, where this coupling could be exploited for laser-induced trans-to-cis isomerization. Strong isotopic effects are observed: deuteration of the hydroxyl group, i.e., in HCOOD and DCOOD, destroys the C–O stretch to torsion mode coupling whereas in DCOOH, little to no effect is observed. [ABSTRACT FROM AUTHOR]

A pure rotational spectrum of methyl p-tolyl sulfoxide (MTSO) was studied using chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 18–26 GHz. A single conformer was unambiguously observed in the supersonic jet expansion, which is consistent with the conformational analysis performed using quantum-chemical calculations. Rotational transitions were split into two components of A and E symmetries due to the low-barrier internal rotation of the ring methyl group [V3 = 11.0178(23) cm−1]. The low energy barrier for the methyl top internal rotation implies an electron-withdrawing effect of the group at the opposite side of the phenyl ring, in comparison with other para-substituted toluenes. The effective ground state (r0) geometry was derived using the rotational constants from the parent species and the 34S and eight 13C singly substituted isotopologues. Compared to two other sulfoxides, methyl phenyl sulfoxide and methyl 4-nitrophenyl sulfoxide, the sulfoxide group in MTSO is slightly more twisted with respect to the plane of the phenyl ring, which could be attributed to the moderate electron-donating effect of the p-methyl group. Furthermore, the pyramidal inversion that interconverts the handedness at the sulfur stereogenic center was explored in the electronic ground (S0) and excited (S1) states with nudged elastic band and time-dependent density functional theory methods. It was found that the pyramidal inversion in S1 is easier than in S0, showing that optical excitation to S1 will facilitate an effectively barrier-free inversion. [ABSTRACT FROM AUTHOR]

We have examined the structure of supercooled liquid D2O as a function of temperature between 185 and 255 K using pulsed laser heating to rapidly heat and cool the sample on a nanosecond timescale. The liquid structure can be represented as a linear combination of two structural motifs, with a transition between them described by a logistic function centered at 218 K with a width of 10 K. The relaxation to a metastable state, which occurred prior to crystallization, exhibited nonexponential kinetics with a rate that was dependent on the initial structural configuration. When the temperature is scaled by the temperature of maximum density, which is an isostructural point of the isotopologues, the structural transition and the non-equilibrium relaxation kinetics of D2O agree remarkably well with those for H2O. [ABSTRACT FROM AUTHOR]

Water molecules trapped in rare gas matrices exhibit conspicuous shifts in their far-infrared (FIR), rotranslational spectral features compared with the corresponding transitions observed in the gas phase. These confinement-induced perturbations have been related not only to the quantization of translational motion but also to the coupling between the orientational and positional degrees of freedom: the rotation–translation coupling (RTC). As the propensity displayed by the nuclear spin isomers (NSI) of water to undergo interconversion in confinement is intimately related to how its nuclear spin degrees of freedom are coupled with those for intra- and intermolecular motions, confinement-induced RTC should also strongly impact the NSI interconversion mechanisms and rates. Insight into the rotranslational dynamics for H 2 16 O , H 2 17 O , and H 2 18 O , confined in argon and krypton matrices, is provided here based on the evolution of rotranslational spectra induced by NSI interconversion while a definitive assignment is provided from the transition energies and intensities calculated using the confined rotor model [Paper I, Wespiser et al., J. Chem. Phys. 156, 074304 (2021)]. In order to build a complete rotranslational energy diagram of confined water, which is fundamental to understand the NSI interconversion rates, the energy difference between the ground ortho and para rotranslational states is derived from the temperature dependence of the intensity ratio of mid-infrared lines emerging from these states. These investigations should provide deeper insight of the factors that control NSI interconversion of water isotopologues under extreme confinement. [ABSTRACT FROM AUTHOR]

The potential interstellar medium molecule, thiirane, has received considerable attention of experimental and theoretical studies in recent years. The anharmonic force field and spectroscopic constants of thiirane are calculated using CCSD(T) and B3LYP methods employing correlation consistent basis sets. Molecular structure, ground state rotational constants, quartic and sextic centrifugal distortion constants, and fundamental frequencies of thiirane are compared with the available experimental data. The B3LYP and CCSD(T) results can reproduce them well. The rotational parameters and vibrational wave numbers of isotopologues for thiirane are also determined using B3LYP method. The new data obtained in this study might be used to assist astronomical search for thiirane. [ABSTRACT FROM AUTHOR]

The phase diagrams for the light H2O, heavy D2O water, and inert substances (Ne, Ar, Kr, and Xe) have been compared. A method of choosing the starting point for entropy and internal energy was proposed. It allowed testing the principle of corresponding states using caloric variables. In the given coordinates of temperature, pressure, and chemical potential, the water isotopologues form one group of substances and have similar phase diagrams. The inert substances in the same coordinates form another group of substances with similar phase diagrams. The phase diagrams for inert Ne with significant de Boer quantum parameters differ to a certain extent from the phase diagrams of other inert substances. [ABSTRACT FROM AUTHOR]

Stable water isotopes are used to infer changes in the hydrological cycle for different climate periods and various climatic archives. Following previous developments of δ18 O in the coupled climate model of intermediate complexity, iLOVECLIM, we present here the implementation of the 1 H 2 H 16 O and 1 H 2 17 O water isotopes in the different components of this model and calculate the associated secondary markers deuterium excess (d-excess) and oxygen-17 excess (17 O-excess) in the atmosphere and ocean. So far, the latter has only been modelled by the atmospheric model LMDZ4. Results of a 5000-year equilibrium simulation under preindustrial conditions are analysed and compared to observations and several isotope-enabled models for the atmosphere and ocean components. In the atmospheric component, the model correctly reproduces the first-order global distribution of the δ2 H and d-excess as observed in the data (R=0.56 for δ2 H and 0.36 for d-excess), even if local differences are observed. The model–data correlation is within the range of other water-isotope-enabled general circulation models. The main isotopic effects and the latitudinal gradient are properly modelled, similarly to previous water-isotope-enabled general circulation model simulations, despite a simplified atmospheric component in iLOVECLIM. One exception is observed in Antarctica where the model does not correctly estimate the water isotope composition, a consequence of the non-conservative behaviour of the advection scheme at a very low moisture content. The modelled 17 O-excess presents a too-important dispersion of the values in comparison to the observations and is not correctly reproduced in the model, mainly because of the complex processes involved in the 17 O-excess isotopic value. For the ocean, the model simulates an adequate isotopic ratio in comparison to the observations, except for local areas such as the surface of the Arabian Sea, a part of the Arctic and the western equatorial Indian Ocean. Data–model evaluation also presents a good match for the δ2 H over the entire water column in the Atlantic Ocean, reflecting the influence of the different water masses. [ABSTRACT FROM AUTHOR]