Gas-phase Properties Research Articles

Could organoaluminium complexes act as prominent TADF emitters for designing efficient diode devices? A DFT/TDA simulation study

Theoretical calculations suggest possible designs of Thermally Activated Delayed Fluorescence (TADF) emitters using three-coordinate aluminium (Al-X3) complexes for the design of organometal light emitting diodes. We investigate the optical properties of gas-phase and toluene-solvated Ac-Al, Ac-Al-F, Ac-Al-CN and Ac-Al-NO2 complexes using DFT/TDA methods. All calculations were carried out using the long-range corrected ωB97XD functional with optimal ω values. Except for Ac-Al-CN contender, the aluminum atom has magnified the spin–orbit couplings between the excited singlet (S1) and triplet (T1) states. The decrease in the reorganization energies of Ac-Al-CN and Ac-Al-NO2 complexes has maximized their reverse intersystem crossing rate constants. The presence of the strong electron withdrawing nitro group has further stabilized its LUMO together with improving both its oscillator strength and the emission decay rate constant. This contender is predicted to be the most prominent TADF emitter and highly promising for designing diode devises amongst the understudy complexes.

Crystal structure and hydrogen sorption properties of Nd0.5Y0.5MgNi4-xCox alloys (x = 0–3)

The gas-phase and electrochemical hydrogenation properties of Nd0.5Y0.5MgNi4-xCox (where x varies from 0 to 3) were studied. Samples were prepared using sintering and annealing procedures. X-ray diffraction analysis indicated that all the alloys were single-phase. The alloys readily absorbed hydrogen, and the crystal structures of the resulting saturated hydrides were refined. Nd0.5Y0.5MgNi4H4.2 and Nd0.5Y0.5MgNi3CoH4.4 belong to the NdMgNi4H3.6 structural type, while Nd0.5Y0.5MgNi2Co2H5.5 and Nd0.5Y0.5MgNiCo3H6.0 belong to the LaMgNi4H4.85 structural type. Electrochemical studies revealed that the maximum discharge capacity of Nd0.5Y0.5MgNi4-xCox electrodes increased from 236 mAh/g to 328 mAh/g as the cobalt content increased. The high-rate dischargeability (HRD1000) initially decreased from 48 % to 7 % with increasing cobalt content, but then increased to 32 % at the highest cobalt concentration. Additionally, the electrochemical kinetic properties were determined and compared for these electrodes, including the charge-transfer resistance (Rct), polarization resistance (Rp), exchange current density (I0), limiting current density (IL), and hydrogen diffusion coefficient (DH).

Topological structures and adsorption properties of the [Fe4S4] clusters

The [Fe4S4] compositions are ubiquitous in biological systems as integral parts of the complex catalytic mechanisms as in hydrogenases and nitrogenases. The current reports about [Fe4S4] species are based on the cube-like structure framework. Here, the topological structures, stability and electronic properties of gas phase [Fe4S4]+, [Fe4S4]0 and [Fe4S4]− are analyzed. It is found that ground state structures of these three clusters have similar cubic cages but different symmetries and spin multiplicities. The molecular dynamics simulations demonstrate that the cubic cage remains thermodynamically stable at 700 K. The density of states show that the charge state is the key to affect electronic behaviors of them even under the same structural framework. The molecular orbitals show that the LUMO orbitals are distributed throughout whole structures, showing great delocalized characteristics, especially for the anionic [Fe4S4]−, while the HOMO orbits are mainly localized in Fe-S bonds, which are also confirmed by the electron localization function analyses. After one CO molecule is adsorbed on these clusters, it prefers to locate at the Fe atoms. Moreover, the C–O bond length and vibration frequency of the [Fe4S4]−-CO undergone a significant red shift. Our work shows that the [Fe4S4]− may act as a potential catalyst for activating the C–O bond.

Unveiling the Multifaceted Nature of 4‐(4‐Methylphenyl Thio)benzophenone: Electronic Structure and Excited States in Gas Phase and Solvents

AbstractBenzophenone and its derivatives are widely used as UV filters and UV‐ink photoinitiators. The photoinitiating properties of benzophenones depend on their degree of conjugation and delocalization within the molecule. By understanding how conjugation, delocalization, and different substituents affect these properties, benzophenone derivatives can be customized for specific applications. Using quantum mechanical calculations based on B3LYP/6‐311++G(d, p) density functional theory (DFT), chemical reactivity, stability, and photoinitiating capabilities of 4‐(4‐methylphenylthio)benzophenone are analyzed. This includes studying its physical and chemical properties in the gas phase, as well as its excited state electronic transitions, vibrational characteristics, and spectroscopic properties both in gas phase and in various solvents. The DFT‐computed infrared spectra match experimental results. The UV/Visible spectra shows absorption towards longer wavelengths due to extended delocalization of π‐electrons. In different solvents with varying polarity, the absorption spectra exhibit high‐intensity peaks, shift in excitation energy and wavelengths based on the polarity of the solvent. This knowledge allows for the development of novel initiators with customized light absorption, excited state lifetimes, and reaction selectivities, which can enhance processes like UV‐curing, photopolymerization, and other light‐driven reactions.

Structural and bonding analysis of PtO2− anion and neutral clusters

This study investigates the structures and bonding properties of gas-phase PtO2ˉ anion and PtO2 neutral using anion photoelectron spectroscopy and theoretical calculations. Notably, both species adopt a D∞h symmetric linear O−Pt−O structure, with PtO2 neutral featuring notably shorter Pt–O bond lengths. Charge transfer from the central Pt atom to the terminal O2 motifs is evident in both clusters, as indicated by Natural Population Analysis (NPA). Chemical bonding analysis reveals σ and π double bonding patterns in PtO2ˉ anion, while PtO2 neutral demonstrates σ and π antiaromaticity. This research enhances our understanding of platinum oxide clusters and their potential in developing co-catalysts for efficient solar-driven water splitting.

A Lumped Model of Water and Heat Transport in a PEMFC Fuel Cell and the Associated Methods for Estimating the Effective Transport Parameters

The fine and quantitative modelling of the coupled phenomena of water and oxygen transport and heat and charge transfer in PEMFCs is difficult from a practical point of view because the interfaces between the different layers are heterogeneous and difficult to characterize. They depend in particular on the mechanical stress field. Moreover, the two-phase flows in the porous layers and feeding channels are by nature stochastic and very difficult to predict. This fine modelling requires a perfect knowledge of the geometry, mechanical and thermal properties, wettability, etc... of the materials, their interfaces and their heterogeneity in space and time. Most of these parameters are unknown and so numerous that it is impossible to estimate them independently of each other by simple experiments. Based on this observation, our philosophy is to develop simple models whose effective transport parameters can be estimated by experiments carried out in situ, for real operating conditions [1]. These models are lumped models that depend on few parameters which integrate the properties of the interfaces. In this presentation, we propose a one-dimensional coupled water and heat transport model (adapted to a differential cell), associated with methods for estimating the unknown water transport and heat transfer parameters. The estimation of the parameters is performed in situ, for an imposed flow field geometry and clamping force. Original experiments are developed to decorrelate the effective diffusion coefficients in the gas phase, adsorbed phase and heat transport properties. The estimation of the parameters is based on simple water balances, i.e. a measurement of the quantities of water leaving the anode and cathode. The model and the experimental set-up are presented. The inverse technique of parameter estimation is detailed. Different materials are implemented in order to observe the resulting impact on the estimated effective transport coefficients. Acknowledgements The authors gratefully acknowledge the financial support of the Lorraine Université d’Excellence program.

The impact of La/Y and Ni/Co substitutions on the gas-phase and electrochemical hydrogenation properties of the La3-xMgxNi9 alloys

This paper presents the results of investigations of the impact of elemental substitution on the hydrogenation properties of La3-xMgxNi9-based alloys, focusing on both gas-phase and electrochemical hydrogenation processes. Alloys derived from La3-xMgxNi9 with La → Y and Ni → Co substitutions were synthesized using powder metallurgy methods. All of them were crystallized with PuNi3 structure type. Gas-phase hydrogenation studies revealed that Y-free samples exhibited faster gas-phase hydrogenation rates compared to Y-substituted ones, whereas electrochemical performance measurements showed the opposite behaviour. Notably, the La1.5Y0.5MgNi6Co3 alloy demonstrated a discharge capacity of approximately 400 mAh/g, while the La1.5Y0.5MgNi7Co2 alloy exhibited good cyclic stability with a discharge capacity of 389.5 mAh/g and preserved approximately 84% of its capacity after 50 charge/discharge cycles at a current density of 50 mA/g. Y-containing samples demonstrated improved electrochemical characteristics, especially in terms of the HRD (high-rate dischargeability) parameter. The La1.5Y0.5MgNi9 alloy has shown ∼86% of its maximum discharge capacity at 1 A/g current density. This electrode with the highest HRD rate demonstrated highest diffusion coefficient (DH = 2.67·10−11 cm2/s), which also correlates with the highest value of exchange current density (I0 = 222 mA/g) and higher limit of the anodic current (IL=878 mA/g). This highlights the prospects of application of Y-containing alloys for areas where high-rate discharge capabilities are required for Ni-MH batteries.

Multiphase neutral interstellar medium: analysing simulation with H i 21cm observational data analysis techniques

ABSTRACT Several different methods are regularly used to infer the properties of the neutral interstellar medium (ISM) using atomic hydrogen (H i) 21cm absorption and emission spectra. In this work, we study various techniques used for inferring ISM gas phase properties, namely the correlation between brightness temperature and optical depth (TB(v), τ(v)) at each channel velocity (v), and decomposition into Gaussian components, by creating mock spectra from a 3D magnetohydrodynamic simulation of a two-phase, turbulent ISM. We propose a physically motivated model to explain the TB(v) − τ(v) distribution and relate the model parameters to properties like warm gas spin temperature and cold cloud length-scales. Two methods based on Gaussian decomposition – using only absorption spectra and both absorption and emission spectra – are used to infer the column density distribution as a function of temperature. In observations, such analysis reveals the puzzle of large amounts (significantly higher than in simulations) of gas with temperature in the thermally unstable range of ∼200–2000 K and a lack of the expected bimodal (two-phase) temperature distribution. We show that, in simulation, both methods are able to recover the actual gas distribution in the simulation till temperatures ≲2500 K (and the two-phase distribution in general) reasonably well. We find our results to be robust to a range of effects such as noise, varying emission beam size, and simulation resolution. This shows that the observational inferences are unlikely to be artefacts, thus highlighting a tension between observations and simulations. We discuss possible reasons for this tension and ways to resolve it.

Cold atomic gas identified by H I self-absorption

Context. Stars form in the dense interiors of molecular clouds. The dynamics and physical properties of the atomic interstellar medium (ISM) set the conditions under which molecular clouds and eventually stars form. It is, therefore, critical to investigate the relationship between the atomic and molecular gas phase to understand the global star formation process. Aims. Using the high angular resolution data from The H I/OH/Recombination (THOR) line survey of the Milky Way, we aim to constrain the kinematic and physical properties of the cold atomic hydrogen gas phase toward the inner Galactic plane. Methods. H I self-absorption (HISA) has proven to be a viable method to detect cold atomic hydrogen clouds in the Galactic plane. With the help of a newly developed self-absorption extraction routine (astroSABER), we built upon previous case studies to identify H I self-absorption toward a sample of giant molecular filaments (GMFs). Results. We find the cold atomic gas to be spatially correlated with the molecular gas on a global scale. The column densities of the cold atomic gas traced by HISA are usually on the order of 1020 cm−2 whereas those of molecular hydrogen traced by 13CO are at least an order of magnitude higher. The HISA column densities are attributed to a cold gas component that accounts for a fraction of ~5% of the total atomic gas budget within the clouds. The HISA column density distributions show pronounced log-normal shapes that are broader than those traced by H I emission. The cold atomic gas is found to be moderately supersonic with Mach numbers of approximately a few. In contrast, highly supersonic dynamics drive the molecular gas within most filaments. Conclusions. While H I self-absorption is likely to trace just a small fraction of the total cold neutral medium within a cloud, probing the cold atomic ISM by the means of self-absorption significantly improves our understanding of the dynamical and physical interaction between the atomic and molecular gas phase during cloud formation.

Vibrational characterization of active drug to the treatment of chagas disease, benznidazole by using force fields and internal coordinates

Two experimental structures of benznidazole active drug used to the treatment of Chagas disease have been structurally characterized and its vibrational spectra completely assigned combining B3LYP/6-311++G** calculations with the experimental FT-IR and FT-Raman spectra and the SQMFF methodology. The most stable conformer of benznidazole found in the study of the potential energy surface is in agreement with that experimentally observed by X-ray diffraction at room temperature while the other one was observed with the heating up to 195 ºC. Both differs in the positions of CH2 groups of acetamide fragment. Their structural properties in gas phase and ethanol solution were computed by using natural bond orbital (NBO), atoms in molecules (AIM), Merz-Kollman (MK) charges, molecular electrostatic potentials (MEP) and frontier orbitals calculations by using the hybrid B3LYP method and the 6-31G* and 6-311++G** basis sets. Additional WB97XD/6-311++G** calculations show that the energy values optimized for the most stable species in both media present lower values than the obtained with the B3LYP/6-31G* method. The vibrational assignments for those two conformers in both media were obtained from their corresponding harmonic force fields together with the scaled force constants.

Development of Imidazolium-Based Parameters for AMOEBA-IL.

A new approach for the efficient parametrization of the polarizable ionic liquid potential AMOEBA-IL and its application to develop parameters for imidazolium-based cations is presented. The new approach relies on the development of parameters for fragments that can be transferred to generate new molecules. The parametrization uses the original AMOEBA-IL parametrization approach, including the use of Gaussian electrostatic model-distributed multipoles (GEM-DM) for the permanent multipoles and approximation of the van der Waals parameters using quantum mechanics energy decomposition analysis (QM-EDA) data. Based on this, functional groups of the selected initial structures are employed as building blocks to develop parameters for new imidazolium-based cations (symmetric or asymmetric) with longer alkyl chains. The parameters obtained with this proposed method were compared with intermolecular interactions from QM references via energy decomposition analysis using symmetry adapted perturbation theory (SAPT) and counterpoise-corrected total intermolecular interactions. The validation of the new parametrized cations was carried out by running molecular dynamics simulations on a series of imidazolium-based ionic liquids with different anions to compare selected thermodynamic and transport properties, including density ρ, enthalpy of vaporization ΔHvap, radial distribution function g(r), and diffusion coefficients D±, with experimental data. Overall, the calculated gas-phase and bulk properties show good agreement with the reference data. The new procedure provides a straightforward approach to generating the required AMOEBA-IL parameters for any imidazolium-based cation.

Magnetic sustentation as an adsorption characterization technique for paramagnetic metal-organic frameworks

Nowadays, there are many reliable characterization techniques for the study of adsorption properties in gas phase. However, the techniques available for the study of adsorption processes in solution, rely on indirect characterization techniques that measure the adsorbate concentration remaining in solution. In this work, we present a sensing method based on the magnetic properties of metal-organic frameworks (MOFs) containing paramagnetic metal centres, which stands out for the rapidity, low cost and in situ direct measurement of the incorporated adsorbate within the porous material. To illustrate this sensing technique, the adsorption in solution of four MOFs have been characterized: MIL-88A(Fe), MOF-74(Cu, Co) and ZIF-67(Co). Our simple and efficient method allows the direct determination of the adsorbed mass, as well as the measurement of adsorption isotherm curves, which we hope will greatly advance the study of adsorption processes in solution, since this method is independent of the chemical nature of the adsorbate that often makes its quantification difficult.

Molecular Dynamics Study of CO2 Phase Change Transport in the Near-Critical Region: Model Parameter Optimization

The technical development of supercritical CO2, energy systems, CO2 capture, and other applications has become a hot topic in recent years. Therefore, molecular dynamics simulation (MD) of CO2, especially the investigation at the CO2 supercritical region is urgently needed. This study focused on the optimization of common CO2 potential model EPM2 (elementary physical model—2) combined MD forcefield OPLS-AA (optimized potentials for liquid simulations—all atom) and CHARMM (chemistry at Harvard macromolecular mechanics for MD simulation). Through adjusting angle parameters according to EPM2, vapor-liquid equilibrium curve, critical point and supercritical region could be well corresponding with experiments, which can be more accurate than previous approaches. The simulated results using 179.63° in OPLS-AA forcefield can not only correspond to supercritical phase of near-critical region (within ±10% error range under CO2 is at 468 kg/m3, 304.2–320 K, 7.2–10.0 MPa), but also be consistent with actual CO2 properties in gas phase of near-critical region (temperature range can reach 304.2–350 K while the density scope can reach 15–168 kg/m3). Besides, optimized potential model also has a certain reliability on the investigation of CO2 diffusion properties. The values simulated have the same order of magnitude as literature values, especially simulated diffusion coefficient values at gas phase. The CO2 property of heat capacity is also simulated, and the errors are within ±15%. That is to say, the optimized CO2 potential parameter also has a certain accuracy to analyze CO2 heat transfer. The angle value optimized in this study may be useful for the fundamental understanding of the supercritical state and it can well be applied in the further investigation of CO2 systems.

Improving Condensed-Phase Water Dynamics with Explicit Nuclear Quantum Effects: The Polarizable Q-AMOEBA Force Field.

We introduce a new parametrization of the AMOEBA polarizable force field for water denoted Q-AMOEBA, for use in simulations that explicitly account for nuclear quantum effects (NQEs). This study is made possible thanks to the recently introduced adaptive Quantum Thermal Bath (adQTB) simulation technique which computational cost is comparable to classical molecular dynamics. The flexible Q-AMOEBA model conserves the initial AMOEBA functional form, with an intermolecular potential including an atomic multipole description of electrostatic interactions (up to quadrupole), a polarization contribution based on the Thole interaction model and a buffered 14-7 potential to model van der Waals interactions. It has been obtained by using a ForceBalance fitting strategy including high-level quantum chemistry reference energies and selected condensed-phase properties targets. The final Q-AMOEBA model is shown to accurately reproduce both gas-phase and condensed-phase properties, notably improving the original AMOEBA water model. This development allows the fine study of NQEs on water liquid phase properties such as the average H-O-H angle compared to its gas-phase equilibrium value, isotope effects, and so on. Q-AMOEBA also provides improved infrared spectroscopy prediction capabilities compared to AMOEBA03. Overall, we show that the impact of NQEs depends on the underlying model functional form and on the associated strength of hydrogen bonds. Since adQTB simulations can be performed at near classical computational cost using the Tinker-HP package, Q-AMOEBA can be extended to organic molecules, proteins, and nucleic acids opening the possibility for the large-scale study of the importance of NQEs in biophysics.

HI-H2 transition: Exploring the role of the magnetic field

Context. Atomic gas in the diffuse interstellar medium (ISM) is organized in filamentary structures. These structures usually host cold and dense molecular clumps. The Galactic magnetic field is considered to play an important role in the formation of these clumps. Aims. Our goal is to explore the role of the magnetic field in the HI-H2 transition process. Methods. We targeted a diffuse ISM filamentary cloud toward the Ursa Major cirrus where gas transitions from atomic to molecular. We probed the magnetic field properties of the cloud with optical polarization observations. We performed multiwavelength spectroscopic observations of different species in order to probe the gas phase properties of the cloud. We observed the CO (J = 1−0) and (J = 2−1) lines in order to probe the molecular content of the cloud. We also obtained observations of the [C ii] 157.6µm emission line in order to trace the CO-dark H2 gas and estimate the mean volume density of the cloud. Results. We identified two distinct subregions within the cloud. One of the regions is mostly atomic, while the other is dominated by molecular gas, although most of it is CO-dark. The estimated plane-of-the-sky magnetic field strength between the two regions remains constant within uncertainties and lies in the range 13–30 µG. The total magnetic field strength does not scale with density. This implies that gas is compressed along the field lines. We also found that turbulence is trans-Alfvénic, with MA ≈ 1. In the molecular region, we detected an asymmetric CO clump whose minor axis is closer, with a 24° deviation, to the mean magnetic field orientation than the angle of its major axis. The H i velocity gradients are in general perpendicular to the mean magnetic field orientation except for the region close to the CO clump, where they tend to become parallel. This phenomenon is likely related to gas undergoing gravitational infall. The magnetic field morphology of the target cloud is parallel to the H i column density structure of the cloud in the atomic region, while it tends to become perpendicular to the H i structure in the molecular region. On the other hand, the magnetic field morphology seems to form a smaller offset angle with the total column density shape (including both atomic and molecular gas) of this transition cloud. Conclusions. In the target cloud where the H i–H2 transition takes place, turbulence is trans-Alfvénic, and hence the magnetic field plays an important role in the cloud dynamics. Atomic gas probably accumulates preferentially along the magnetic field lines and creates overdensities where molecular gas can form. The magnetic field morphology is probed better by the total column density shape of the cloud, and not its H i column density shape.

Large Eddy Simulation of a Reacting Kerosene Spray in Hot Vitiated Cross-Flow

The evaporation and combustion characteristics of a kerosene spray injected perpendicularly into a cross-flow of high-temperature vitiated air is investigated. This fundamental flow configuration has wider implications for the future development of ultra-low emission aeronautical combustors, particularly with respect to technologies involving MILD combustion. Large eddy simulations with a Eulerian–Lagrangian framework are performed to investigate the spray evolution and the characteristics of the reaction zone for a range of conditions. For the closure of turbulence-chemistry interactions at the sub-grid scales, a transported probability density function approach solved by the Eulerian stochastic fields method is applied. A configuration based on the use of airblast atomisation is assessed first and compared with experimental observations. The effect of the atomiser air-to-liquid mass flow ratio is studied in greater detail, both in terms of the resulting gas-phase properties and the droplet evaporation process. Then, the effect of ambient pressure on the global spray flame behaviour is examined. For this part of the study, no atomising air is included in the simulation to separate the effects of ambient pressure on the spray from the interaction with the air jet. Analysis of the flame and spray properties at cross-flow operating pressures of 1 atm, 2 bar and 4 bar highlights the strong coupling between the reacting flow and droplet evaporation characteristics, which are highly affected by the penetration of the spray into a flow field characterised by relatively large gradients of temperature. The results reported in this work provide fundamental understanding for the development of novel low-emission combustion technologies and demonstrate the feasibility of applying large eddy simulation with detailed chemistry for the investigation of reacting aviation fuel sprays in hot vitiated cross-flow.

Longitudinal Relaxation (T 1) of Methane/Hydrogen Mixtures for Operando Characterization of Gas-Phase Reactions.

Catalytic hydrogenation reactions are important in a modern hydrogen-based society. To optimize these gas-phase reactions, a deep understanding of heat, mass, and momentum transfer inside chemical reactors is required. Nuclear magnetic resonance (NMR) measurements can be used to obtain spatially resolved values of temperature, gas composition, and velocity in the usually opaque catalytic macrostructures. For this, the desired values are calculated from measured NMR parameters like signal amplitude, T 1, or T 2. However, information on how to calculate target values from these NMR parameters in gases is scarce, especially for mixtures of gases. To enable detailed NMR studies of hydrogenation reactions, we investigated the T 1 relaxation of methane and hydrogen, which are two gases commonly present in hydrogenation reactions. To achieve industrially relevant conditions, the temperatures are varied from 290 to 600 K and the pressure from 1 bara to 5 bara, using different mixtures of methane and hydrogen. The results show that hydrogen, which is usually considered to be nondetectable in standard MRI sequences, can be measured at high concentrations, starting at a pressure of 3 bara even at temperatures above 400 K. In the investigated parameter range, the absolute T 1 values of hydrogen show only small dependence on temperature, pressure, and composition, while T 1 of methane is highly dependent on all three parameters. At a pressure of 5 bara, the measured values of T 1 for methane agree very well with theoretical predictions, so that they can also be used for temperature calculations. Further, it can be shown that the same measurement technique can be used to accurately calculate gas ratios inside each voxel. In conclusion, this study covers important aspects of spatially resolved operando NMR measurements of gas-phase properties during hydrogenation reactions at industrially relevant conditions to help improve chemical processes in the gas phase.

Protomer Formation Can Aid the Structural Identification of Caffeine Metabolites.

The structural annotation of isomeric metabolites remains a key challenge in untargeted electrospray ionization/high-resolution mass spectrometry (ESI/HRMS) metabolomic analysis. Many metabolites are polyfunctional compounds that may form protomers in electrospray ionization sources and therefore yield multiple peaks in ion mobility spectra. Protomer formation is strongly structure-specific. Here, we explore the possibility of using protomer formation for structural elucidation in metabolomics on the example of caffeine, its eight metabolites, and structurally related compounds. It is observed that two-thirds of the studied compounds formed high- and low-mobility species in high-resolution ion mobility. Structures in which proton hopping was hindered by a methyl group at the purine ring nitrogen (position 3) yielded structure-indicative fragments with collision-induced dissociation (CID) for high- and low-mobility ions. For compounds where such a methyl group was not present, a gas-phase equilibrium could be observed for tautomeric species with two-dimensional ion mobility. We show that the protomer formation and the gas-phase properties of the protomers can be related to the structure of caffeine metabolites and facilitate the identification of the structural isomers.

Numerical analysis of dilute methanol spray flames in vitiated coflow using extended flamelet generated manifold model

This work focuses on the large eddy simulation and the study of turbulent dilute methanol spray flames in vitiated coflow using the secondary-oxidizer Flamelet Generated Model (FGM). The modified FGM model uses an additional secondary oxidizer parameter in addition to the three other parameters previously used for spray flames—progress variable, mixture fraction, and enthalpy. The results for gas phase and droplet properties are validated against the dilute methanol spray flame database for varying fuel injection amounts. The droplet statistics and the liftoff flame heights are accurately captured for all the cases. A proper orthogonal decomposition (POD) of the scalar fluctuating hydroxyl radical (OH) field and the velocity–temperature field captures the flame structures in the downstream region of ignition kernels. The detailed POD analysis reveals that the base frequency of the dominant OH field equals that of the dominant vortical structure of 67.3 Hz. The flame propagation happens around these dominant vortical structures because of the less-strained fluid mixing.

Assessing the persistence of chalcogen bonds in solution with neural network potentials.

Non-covalent bonding patterns are commonly harvested as a design principle in the field of catalysis, supramolecular chemistry, and functional materials to name a few. Yet, their computational description generally neglects finite temperature and environment effects, which promote competing interactions and alter their static gas-phase properties. Recently, neural network potentials (NNPs) trained on density functional theory (DFT) data have become increasingly popular to simulate molecular phenomena in condensed phase with an accuracy comparable to ab initio methods. To date, most applications have centered on solid-state materials or fairly simple molecules made of a limited number of elements. Herein, we focus on the persistence and strength of chalcogen bonds involving a benzotelluradiazole in condensed phase. While the tellurium-containing heteroaromatic molecules are known to exhibit pronounced interactions with anions and lone pairs of different atoms, the relevance of competing intermolecular interactions, notably with the solvent, is complicated to monitor experimentally but also challenging to model at an accurate electronic structure level. Here, we train direct and baselined NNPs to reproduce hybrid DFT energies and forces in order to identify what the most prevalent non-covalent interactions occurring in a solute-Cl--THF mixture are. The simulations in explicit solvent highlight the clear competition with chalcogen bonds formed with the solvent and the short-range directionality of the interaction with direct consequences for the molecular properties in the solution. The comparison with other potentials (e.g., AMOEBA, direct NNP, and continuum solvent model) also demonstrates that baselined NNPs offer a reliable picture of the non-covalent interaction interplay occurring in solution.