Hydrogen Exchange Reaction Research Articles

Simulation of Chemical Reactions on a Quantum Computer.

Studying chemical reactions, particularly in the gas phase, relies heavily on computing scattering matrix elements. These elements are essential for characterizing molecular reactions and accurately determining reaction probabilities. However, the intricate nature of quantum interactions poses challenges, necessitating the use of advanced mathematical models and computational approaches to tackle the inherent complexities. In this study, we develop and apply a quantum computing algorithm for the calculation of scattering matrix elements. In our approach, we employ the time-dependent method based on the Møller operator formulation where the S-matrix element between the respective reactant and product channels is determined through the time correlation function of the reactant and product Møller wavepackets. We successfully apply our quantum algorithm to calculate scattering matrix elements for 1D semi-infinite square well potential and on the colinear hydrogen exchange reaction. As we navigate the complexities of quantum interactions, this quantum algorithm is general and emerges as a promising avenue, shedding light on new possibilities for simulating chemical reactions on quantum computers.

High-Resolution Crossed-Beam Dynamics Studies of the D + Para-H2 → HD + H Reaction at 1.21 eV.

Understanding kinetic isotope effects is important in the study of the reaction dynamics of elementary chemical reactions, particularly those involving hydrogen atoms and molecules. As one of the isotopic variants of the hydrogen exchange reaction, the D + para-H2 reaction has attracted much attention. However, experimental studies of this reaction have been limited primarily due to its strong experimental background noise. In this study, by using the velocity map ion imaging method and the near-threshold ionization technique, together with improvements on the vacuum condition in the vicinity of the collision zone, background noise was reduced significantly, and quantum state-resolved differential cross sections (DCSs) for the D + para-H2 reaction at a collision energy of 1.21 eV were acquired in a crossed molecular beams experiment. Interestingly, clear rotational state-dependent angular distributions were noticed in the quantum state-resolved DCSs. The most intense peak's positions for HD (v', j') products shift to different scattering directions as the product's ro-vibrational quantum number increases. Two different microscopic reaction mechanisms are found to be involved in this reaction for HD products in different vibrational states. The results show a direct correlation between the scattering angle and the product's rotational quantum number, revealing that the contributions of impact parameters are strongly influenced by the corresponding centrifugal barrier.

Observation of geometric phase effect through backward angular oscillations in the H + HD → H2 + D reaction

Quantum interference between reaction pathways around a conical intersection (CI) is an ultrasensitive probe of detailed chemical reaction dynamics. Yet, for the hydrogen exchange reaction, the difference between contributions of the two reaction pathways increases substantially as the energy decreases, making the experimental observation of interference features at low energy exceedingly challenging. We report in this paper a combined experimental and theoretical study on the H + HD → H2 + D reaction at the collision energy of 1.72 eV. Although the roaming insertion pathway constitutes only a small fraction (0.088%) of the overall contribution, angular oscillatory patterns arising from the interference of reaction pathways were clearly observed in the backward scattering direction, providing direct evidence of the geometric phase effect at an energy of 0.81 eV below the CI. Furthermore, theoretical analysis reveals that the backward interference patterns are mainly contributed by two distinct groups of partial waves (J ~ 10 and J ~ 19). The well-separated partial waves and the geometric phase collectively influence the quantum reaction dynamics.

Hydrophobically modified ceramic-supported Pt-particle catalyst for enhanced water–hydrogen exchange reactions

Hydrophobic catalysts are key to realizing water–hydrogen exchange reactions. However, current catalysts exhibit low mechanical strength, low utilization rate of Pt particle, and complex preparing process. Thus, further research is required to produce more stable and active catalysts that can be fabricated using simple manufacturing methods. However, the use of a ceramic carrier with a hydrophobic structure is expected to fill this need. Herein, a novel hydrophobically modified ceramic carrier was effectively fabricated by constructing a rough CeO2 surface structure with a low surface energy 1H,1H,2H,2H-perfluorooctyltrimethoxysilane coating. The Pt/hydrophobic-modified ceramic catalyst was then prepared via impregnation method using Pt-precursor solution and H2 reduction. Results revealed that the catalyst exhibited an average Pt particle size of 2.15 nm, and the Pt0 content reached 54.59 %. The catalyst achieved best conversion rate of 98.13 % using a test temperature of 60 °C with a hydrogen flow rate of 0.5 L/min. After testing for 4 weeks, the conversion rate of the novel catalyst decreased by less than 5 %. These results indicate the suitability of hydrophobically modified ceramic for the preparation of novel hydrophobic catalysts with good catalytic activity and stability; therefore, it has good application prospects for water–hydrogen exchange reactions.

Heat charging and discharging of coupled MgH2–LaNi5 based thermal storage: Cycling stability and hydrogen exchange reactions

Heat charging and discharging performances and cycling stability of the coupled MgH2–LaNi5 thermal storage system are investigated. Heat storage reaction is studied by tracking temperatures and pressures of hydride beds as well as hydrogen mass flow rates exchanging between MgH2 and LaNi5. Upon 20 heat storage cycles, MgH2–LaNi5 pair reveals remarkably cycling stability with the energy densities during heat charging and discharging of 797 ± 37.5 and 680 ± 28 kJ/kg, respectively. The hydrogen content exchange between MgH2 and LaNi5 during heat storage cycles is up to 57 % of theoretical hydrogen capacity. The possibilities to enhance the hydrogen contents participating in the heat storage reaction are discussed. The heat charging and discharging performances at different positions in the hydride beds of MgH2–LaNi5 pair are characterized. Not only thermodynamic compatibility of MgH2 and LaNi5 but also kinetics as well as hydrogen and heat transfer in MgH2 beds considerably influence heat storage performance.

Theoretical Calculations of the Thermal Rate Coefficients for the Interstellar NH3+ + H2 → NH4+ + H Reaction on a New Δ-Machine Learning Potential Energy Surface

The NH3+ + H2 → NH4+ + H ion–molecule hydrogen-exchange reaction is important for understanding the mechanisms of ammonia formation in interstellar medium and circumstellar environments. The thermal rate coefficients of this reaction are calculated using the ring polymer molecular dynamics approach, which can account for the nuclear quantum effects, on a newly developed ab initio potential energy surface (PES). The PES was constructed by fitting a large number of ab initio points at the MP2/cc-pVDZ and CCSD(T)/cc-pVTZ levels using a Δ-machine learning approach. The obtained rate coefficients exhibited a minimum at T ∼ 130 K, and this characteristic temperature-dependent behavior qualitatively agreed with the experimental measurements. This study confirms that quantum tunneling plays a significant role in the reaction dynamics along with the existence of the metastable NH3+···H2 pre-reactive complex in the entrance channel of the PES.

Electronic nonadiabatic effects in the state-to-state dynamics of the H + H2 → H2 + H exchange reaction with a vibrationally excited reagent.

Out of the many major breakthroughs that the hydrogen-exchange reaction has led to, electronic nonadiabatic effects that are mainly due to the geometric phase has intrigued many. In this work we investigate such effects in the state-to-state dynamics of the H + H2 (v = 3, 4, j = 0) → H2 (v', j') + H reaction with a vibrationally excited reagent at energies corresponding to thermal conditions. The dynamical calculations are performed by a time-dependent quantum mechanical method both on the lower adiabatic potential energy surface (PES) and also using a two-states coupled diabatic theoretical model to explicitly include all the nonadiabatic couplings present in the 1E' ground electronic manifold of the H3 system. The nonadiabatic couplings are considered here up to the quadratic term; however, the effect of the latter on the reaction dynamics is found to be very small. Adiabatic population analysis showed a minimal participation of the upper adiabatic surface even for the vibrationally excited reagent. A strong nonadiabatic effect appears in the state-to-state reaction probabilities and differential cross sections (DCSs). This effect is manifested as "out-of-phase" oscillations in the DCSs between the results of the uncoupled and coupled surface situations. The oscillations persist as a function of both scattering angle and collision energy in both the backward and forward scattering regions. The origins of these oscillations are examined in detail. The oscillations that appear in the forward direction are found to be different from those due to glory scattering, where the latter showed a negligibly small nonadiabatic effect. The nonadiabatic effects are reduced to a large extent when summed over all product quantum states, in addition to the cancellation due to integration over the scattering angle and partial wave summation.

Exploring Potential Energy Surface with <i>Mathematica</i>: An Algorithmic Demonstration of Minimum Energy Path, Stationary Points and Transition State

The reaction profile (energy profile) is a widely used conceptual tool in chemical kinetics to represent the progress of a chemical reaction. Quantitatively, a reaction profile can be viewed as a minimum energy path (MEP) on the potential energy surface (PES), which connects the reactants and products through one or more transition states or intermediates. In this article, we used Mathematica program to demonstrate a generic method for finding reaction profile on a Müller-Brown PES by applying steepest descent algorithm. The properties of the MEP and stationary points were discussed in detail. The general characteristics of the transition state (TS), and imaginary mode were illustrated with a vibrational analysis of hydrogen exchange reaction, H2+H H+H2.

Photo-Induced Reactions between Glyoxal and Hydroxylamine in Cryogenic Matrices.

In this paper, the photochemistry of glyoxal–hydroxylamine (Gly–HA) complexes is studied using FTIR matrix isolation spectroscopy and ab initio calculations. The irradiation of the Gly–HA complexes with the filtered output of a mercury lamp (λ > 370 nm) leads to their photoconversion to hydroxyketene–hydroxylamine complexes and the formation of hydroxy(hydroxyamino)acetaldehyde with a hemiaminal structure. The first product is the result of a double hydrogen exchange reaction between the aldehyde group of Gly and the amino or hydroxyl group of HA. The second product is formed as a result of the addition of the nitrogen atom of HA to the carbon atom of one aldehyde group of Gly, followed by the migration of the hydrogen atom from the amino group of hydroxylamine to the oxygen atom of the carbonyl group of glyoxal. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structures and vibrational spectra of the identified species.

Organocatalytic Asymmetric Synthesis of Si-Stereogenic Silyl Ethers.

Functionalized enantiopure organosilanes are important building blocks with applications in various fields of chemistry; nevertheless, asymmetric synthetic methods for their preparation are rare. Here we report the first organocatalytic enantioselective synthesis of tertiary silyl ethers possessing “central chirality” on silicon. The reaction proceeds via a desymmetrizing carbon–carbon bond forming silicon–hydrogen exchange reaction of symmetrical bis(methallyl)silanes with phenols using newly developed imidodiphosphorimidate (IDPi) catalysts. A variety of enantiopure silyl ethers was obtained in high yields with good chemo- and enantioselectivities and could be readily derivatized to several useful chiral silicon compounds, leveraging the olefin functionality and the leaving group nature of the phenoxy substituent.

MgH2-based hydrogen storage tank: Kinetics, reversibility, and MWCNTs content

The de/rehydrogenation performance, mechanism, and reversibility of a MgH2-based hydrogen storage tank with enhanced packing volume of up to 337.40 mL have been investigated. Due to significant upscaling, the MWCNTs loading content significantly affects the thermal conductivity and hydrogen diffusion in the tank. By increasing the MWCNTs content from 5 to 10 wt%, the hydrogen sorption kinetics is significantly improved. This has led to an enhancement in the reversible hydrogen capacity from 38.9 to 52.5% of the theoretical value upon 10–15 hydrogen release and uptake cycles. In addition, the de/rehydrogenation behavior at different positions in the radial and axial directions of the tank have been studied by tracking temperature and pressure changes observed during the hydrogen exchange reaction and studying the chemical compositions of the sample after cycling.

Dense radical formation in L-alanine-3,3,3-d3 and L-alanine-d4 by 1.5 keV soft X-ray irradiation

Radicals produced in crystalline L-alanine-3,3,3-d3 and L-alanine-d4 were observed by the electron spin resonance (ESR) technique during 1.5 keV soft X-ray irradiation. The spectral change from •CHCD3COOH to •CDCD3COOH by a hydrogen exchange reaction was directly observed in L-alanine-3,3,3-d3. The line width of the ESR spectra obtained by the soft X-ray irradiation was 1.5 times wider than that of hard X-rays from a previous report, meaning a higher density of radicals. The efficiency of the radical yield by the soft X-ray irradiation was 10−6 relative to that by γ-irradiation. The product formed by the radical recombination was observed by an LC/MS analysis. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, just as the high-LET irradiation by heavy ions. The result was the same as the yield of hydroxyl radicals in an aqueous solution that decreased with the decreasing photon energy from 1.25 MeV to 1.5 keV. We concluded that the high LET nature of the lower energy photons leads to the dense radical formation in the crystalline alanine powder.

The Silicon–Hydrogen Exchange Reaction: Catalytic Kinetic Resolution of 2-Substituted Cyclic Ketones

AbstractWe have recently reported the strong and confined, chiral acid-catalyzed asymmetric ‘silicon−hydrogen exchange reaction’. One aspect of this transformation is that it enables access to enantiopure enol silanes in a tautomerizing σ-bond metathesis, via deprotosilylation of ketones with allyl silanes as the silicon source. However, until today, this reaction has not been applied to racemic, 2-substituted, cyclic ketones. We show here that these important substrates readily undergo a highly enantioselective kinetic resolution furnishing the corresponding kinetically preferred enol silanes. Mechanistic studies suggest the fascinating possibility of advancing the process to a dynamic kinetic resolution.

The evolution of intra- and inter-molecular isotope equilibria in natural gases with thermal maturation

Naturally occurring hydrocarbon fluids in sedimentary basins have economic, geological and environmental significance. Connecting sedimentary basin temperature-time evolution with petroleum generation and transformation is a long-studied problem. In this study, we investigate the use of a novel tool – multiply substituted isotopologues of methane, for distinguishing between different chemical mechanisms in catagenesis and for characterizing the extent of thermal maturation of thermogenic natural gases. We analyze the stable isotope compositions of a suite of thermogenic gas samples that are globally distributed and cover a wide range in composition and thermal maturation, from dominantly unconventional shale gas formations and a few conventional gas plays. Our data show that methane generated at early thermal maturity has a stable isotope composition governed by chemical kinetics, characterized by a pronounced deficit in Δ12CH2D2; this signature can be explained by its formation chemistry that combines a more D-rich methyl radical pool and more D-poor H radical pool. Methane from higher thermal maturity fluids increases in Δ12CH2D2, reaching equilibrium at vitrinite reflectance maturity (Ro) of approximately 1.5% (equivalent to 170–210 °C peak burial temperature) and higher, which is interpreted to be the result of isotope exchange erasing the disequilibrium signature of catagenetic chemistry, mediated by CH activation during either radical chain reactions or organic-inorganic interactions on mineral surfaces. We further examined hydrogen isotope fractionations among methane, ethane and propane for a compiled global dataset and found that the intermolecular fractionation exhibits a trend similar to that seen for the Δ12CH2D2 value of methane, departing from equilibrium at low thermal maturities and moving towards equilibrium as maturity increases. These findings indicate that the inter- and intra-molecular hydrogen isotope structures of components of thermogenic natural gas transition from chemical-kinetic control at low thermal maturities toward thermodynamic control at higher thermal maturities, mediated by hydrogen exchange reactions. We propose that these systematic relationships could be used to identify the exact thermal maturation stages for natural gases and their associated fluids, especially for oil-associated gas at early maturation.

Comparison of Properties of the Hydrophobic Catalyst RCTU-3SM in Reactions of Isotope Exchange Between Hydrogen and Water Vapors and Oxidation of Trace Hydrogen in Gas Flows

A comparative study of the efficiency of the hydrophobic catalyst RCTU-3SM in chemical isotope exchange reactions of hydrogen with water and the oxidation of trace amounts of hydrogen in relation to the detritiation tasks of technological streams was carried out. It is shown that, depending on the equilibrium conditions of the isotope exchange process, there is an optimum temperature at which the reaction rate has a maximum. It was found that the rate of oxidation reaction of trace hydrogen depends on the content of oxygen in the purified stream. With oxygen concentration reducing, the oxidation rate initially increases, and when the ratio of oxygen and hydrogen concentrations is less than 100, the rate remains constant within the experimental error.

Al2O3 ALD films grown using TMA + rare isotope 2[formula omitted]O and 1[formula omitted]O precursors

In this work hydrogen and oxygen migration and exchange reactions in the atomic layer deposited (ALD) Al2O3 thin films were studied together with hydrogen incorporation by varying deposition parameters. Al2O3 films deposited at low temperatures can contain more than 20 at.% of hydrogen. Both higher temperature and longer purge length decrease the hydrogen and carbon concentrations significantly. In order to track the hydrogen and oxygen movement in the films, heavy water (2H216O) and oxygen-18 enriched water (1H218O) were used as precursors in combination with trimethylaluminium (TMA). Different isotopes of the same element were quantified by means of time-of-flight elastic recoil detection analysis (ToF-ERDA). It was found out that 1H/2H exchange reactions take place even at room temperature if the hydrogen concentration is high enough. On the other hand, oxygen atoms in the films do not migrate notably.

Effect of Reagent Vibration and Rotation on the State-to-State Dynamics of the Hydrogen Exchange Reaction, H + H2 → H2 + H.

State-to-state dynamics of the benchmark hydrogen exchange reaction H + H2 (v = 0-4, j = 0-3) → H2 (v', j') + H is investigated with the aid of the real wave packet approach of Gray and Balint-Kurti (J. Chem. Phys. 1998, 108, 950-962) and electronic ground BKMP2 potential energy surface of Boothroyd et al. (J. Chem. Phys. 1996, 104, 7139-7152). Initial state-selected and product state-resolved reaction probabilities, integral cross section, and product diatom vibrational and rotational level populations at a few collision energies are reported to elucidate the energy disposal mechanism. State-specific thermal rate constants are also calculated and compared with the available literature results. Coriolis coupling terms of the nuclear Hamiltonian are included, and calculations are parallelized over the helicity quantum number, Ω'. Attempts are made, in particular, to study the effect of reagent vibrational and rotational excitations on the dynamical attributes. It is found that the calculations become computationally expensive with reagent vibrational and rotational excitation. Reagent vibrational excitation is found to enhance the reactivity and has significant impact on the energy disposal to the vibrational and rotational degrees of freedom of the product. The interplay of reagent translational and vibrational energy on the product vibrational distribution unfolds an important aspect of the energy disposal mechanism. The effect of reagent rotation on the state-to-state dynamics is found not to be very significant, and the weak effect turns out to be specific to v'.

The Silicon-Hydrogen Exchange Reaction: A Catalytic σ-Bond Metathesis Approach to the Enantioselective Synthesis of Enol Silanes.

The use of chiral enol silanes in fundamental transformations such as Mukaiyama aldol, Michael, and Mannich reactions as well as Saegusa–Ito dehydrogenations has enabled the chemical synthesis of enantiopure natural products and valuable pharmaceuticals. However, accessing these intermediates in high enantiopurity has generally required the use of either stoichiometric chiral precursors or stoichiometric chiral reagents. We now describe a catalytic approach in which strongly acidic and confined imidodiphosphorimidates (IDPi) catalyze highly enantioselective interconversions of ketones and enol silanes. These “silicon–hydrogen exchange reactions” enable access to enantiopure enol silanes via tautomerizing σ-bond metatheses, either in a deprotosilylative desymmetrization of ketones with allyl silanes as the silicon source or in a protodesilylative kinetic resolution of racemic enol silanes with a carboxylic acid as the silyl acceptor.

Franck-Condon simulations of transition-state spectra for the OH + H2O and OD + D2O reactions.

We present the results of quantum wave packet calculations performed to analyze the experimental transition-state spectra for the OH + H2O and OD + D2O reactions based on photodetachment of the H3O2- and D3O2- anions. We used a reduced-dimensionality model in which four normal-mode coordinates were considered for the neutral transition state. High-level ab initio potential energy surfaces were used for both the neutral and anionic states. The calculated spectra were found to be in reasonable agreement with the experimental spectra. The present study confirms that the vibrational progression observed experimentally is associated with the antisymmetric motion of the transferred H/D atom. We also found that the O-O stretching motion plays an important role in the transition-state dynamics. The influence of vibrational excitation of the H3O2- and D3O2- anions on the photodetachment spectra was also investigated.

Ensemble-Based Molecular Simulation of Chemical Reactions under Vibrational Nonequilibrium.

We present an approach to incorporate the effect of vibrational nonequilibrium in molecular dynamics (MD) simulations. A perturbed canonical ensemble, in which selected modes are excited to higher temperature while all others remain equilibrated at low temperature, is simulated by applying a specifically tailored bias potential. Our method can be readily applied to any (classical or quantum mechanical) MD setup at virtually no additional computational cost and allows the study of reactions of vibrationally excited molecules in nonequilibrium environments such as plasmas. In combination with enhanced sampling methods, the vibrational efficacy and mode selectivity of vibrationally stimulated reactions can then be quantified in terms of chemically relevant observables, such as reaction rates and apparent free energy barriers. We first validate our method for the prototypical hydrogen exchange reaction and then show how it can capture the effect of vibrational excitation on a symmetric SN2 reaction and radical addition on CO2.