A heat transfer study was conducted,in the framework of Computational Fluid Dynamics(CFD),on a Hot-Wire Chemical Vapour Deposition(HWCVD)reactor chamber to determine a safe deposition distance for atomic hydrogen prod...A heat transfer study was conducted,in the framework of Computational Fluid Dynamics(CFD),on a Hot-Wire Chemical Vapour Deposition(HWCVD)reactor chamber to determine a safe deposition distance for atomic hydrogen produced by HWCVD.The objective of this study was to show the feasibility of using heat transfer simulations in determining a safe deposition distance for deposition of this kind.All CFD simulations were set-up and solved within the framework of the CFD packages of OpenFOAM namely;snappyHexMesh for mesh generation,buoyantSimpleFoam and rhoSimpleFoam as the solvers and paraView as the post-processing tool.Using a standard set of deposition parameters for the production of atomic hydrogen by HWCVD,plots of the gas temperature in the deposition region were produced.From these plots,we were able to determine a safe deposition distance in the HWCVD reactor to be in the range between 3 and 4 cm from the filament.展开更多
The energy spectrum of the hydrogen atom has been applied in calculating the time rate of energy transitions between the quantum states of the atom. The formal basis of the approach has been provided by the quantum pr...The energy spectrum of the hydrogen atom has been applied in calculating the time rate of energy transitions between the quantum states of the atom. The formal basis of the approach has been provided by the quantum properties of energy and time deduced from the Joule-Lenz law. The rates of the energy transitions obtained in this way were compared with the quantum-mechanical probabilities of transitions calculated earlier by Bethe and Condon and Shortley for the same pairs of the quantum states.展开更多
In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless number...In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.展开更多
Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fue...Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fueling the suspected central superrmassive black hole. Although optical images show a number of violently interacting systems, in many cases the evidence for such interactions is only circumstantial (e.g., asymmetric optical morphologies, projected nearby companion galaxies) or not at all apparent. Here we image quasar host galaxies for the first time in the redshifted 21 cm line emission of neutral atomic hydrogen (HI) gas, which in nearby galaxies has proven to be a particularly sensitive as well as enduring tracer of tidal interactions. The three quasars studied have different optical environments normally seen around low reshift quasars, ranging from a perhaps mildly interacting system to a relatively undisturbed host with a projected neighbouring galaxy to an isolated and apparently serene host galaxy. By contrast with their optical appearences, all three quasar host galaxies exhibit ongoing or remnant tidal HI disruptions tracing galactic encounters or mergers. These observations provide a better understanding of the likely stage of their interaction.展开更多
We report a theoretical scheme using a B-spline basis set to improve the poor computational accuracy of circular Rydberg states of hydrogen atoms in the intermediate magnetic field. This scheme can produce high accura...We report a theoretical scheme using a B-spline basis set to improve the poor computational accuracy of circular Rydberg states of hydrogen atoms in the intermediate magnetic field. This scheme can produce high accuracy energy levels and valid for an arbitrary magnetic field. Energy levels of hydrogen are presented for circular Rydberg states with azimuthal quantum numbers ｜m｜ =10-70 as a function of magnetic field strengths ranging from zero to 2.35 × 10^9 T. The variation of spatial distributions of electron probability densities with magnetic field strengths is discussed and competition between Coulomb and magnetic interactions is illustrated.展开更多
A modified uncertainty principle coupling the intervals of energy and time can lead to the shortest distance attained in course of the excitation process, as well as the shortest possible time interval for that proces...A modified uncertainty principle coupling the intervals of energy and time can lead to the shortest distance attained in course of the excitation process, as well as the shortest possible time interval for that process. These lower bounds are much similar to the interval limits deduced on both the experimental and theoretical footing in the era when the Heisenberg uncertainty principle has been developed. In effect of the bounds existence, a maximal nuclear charge Ze acceptable for the Bohr atomic ion could be calculated. In the next step the velocity of electron transitions between the Bohr orbits is found to be close to the speed of light. This result provides us with the energy spectrum of transitions similar to that obtained in the Bohr’s model. A momentary force acting on the electrons in course of their transitions is estimated to be by many orders larger than a steady electrostatic force existent between the atomic electron and the nucleus.展开更多
Electrocatalytic nitrate reduction reaction(NO_(3)RR)to ammonia provides a promising approach to environmental preservation and sustainable energy production,but suffers from a low yield rate and poor Faradic efficien...Electrocatalytic nitrate reduction reaction(NO_(3)RR)to ammonia provides a promising approach to environmental preservation and sustainable energy production,but suffers from a low yield rate and poor Faradic efficiency,ascribed to the sluggish active hydrogen(H^(*))generation via water dissociation.Herein,single Ru atoms anchored Co(OH)_(2)(Ru1/Co(OH)_(2))catalysts are synthesized for selective nitrate reduction to ammonia,which exhibits an excellent NH_(3)yield rate of 4200μg h^(-1)cm^(-2)and a high NH_(3)Faradic efficiency of 97%at-0.33 V versus reversible hydrogen electrode,outperforming the counterpart Co(OH)_(2)and the mostly reported electrocatalysts.Experimental and theoretical results reveal that the addition of Ru atoms can boost H^(*)generation and decrease the hydrogenation energy barrier on Ru1/Co(OH)_(2),leading to enhanced NO_(3)RR performance.An integrated system of electrochemical NO_(3)RR electrolyzer and in-situ NH_(3)recovery is present,where the electrochemical NO_(3)RR can be coupled with a hydrazine oxidation reaction to achieve a more highly efficient and electricity-saving system for NH_(3)recovery.This work provides guidance for the rational design of high-performance NO_(3)RR electrocatalysts by the effective regulation of H^(*)generation and holds great promise for simultaneous nitrate-containing wastewater treatment and resource recovery.展开更多
Atomic hydrogen(H∗)plays a crucial role in electrochemical reduction technology towards various environmental and energy applications,but suffers from low utilization efficiency arisen from the undesirable H-H dimeriz...Atomic hydrogen(H∗)plays a crucial role in electrochemical reduction technology towards various environmental and energy applications,but suffers from low utilization efficiency arisen from the undesirable H-H dimerization and the competitive adsorption between water molecule with reactants on the traditional adjacent catalytic sites.Herein,we anchored Pd single atoms on the naturally formed titanium oxide of titanium foam to construct Pd_(1)-O-Ti dual-site electrocatalyst with spatially isolated water dissociation and H∗utilization site,which synchronously inhibits the H-H dimerization and the competitive adsorption of water molecule and targeted reactants.Experiments and theoretical calculations revealed that the Ti-O sites could synergistically dissociate water to H∗,which overflowed to nearby Pd single-atom sites for designed reduction reactions and utilization benefiting from the hydrogen spillover ability of titanium oxide substrate.These Pd_(1)-O-Ti dual sites delivered almost 100%bromate reduction efficiency with a rate constant of 1.57 h^(-1),far superior to those of Pdn-O-Ti with adjacent Pd sites(0.52 h^(-1)),Pd_(1)-N-C with single sites(0.04 h^(-1))and commercial Pd/C(0.18 h^(-1)),respectively.This study sheds light on the importance of integrating synergistic active sites for complicated electrochemical reactions,and provide new insights in improving H∗ utilization for environmental remediation.展开更多
Here we present a highly efficient protocol utilizing nickel-hydride hydrogen atom transfer catalysis for the regio-and enantioselective hydrofluorination of internal alkenes.This method efficiently assembles a wide a...Here we present a highly efficient protocol utilizing nickel-hydride hydrogen atom transfer catalysis for the regio-and enantioselective hydrofluorination of internal alkenes.This method efficiently assembles a wide array of enantioenrichedβ-fluoro amides with excellent regio-and enantioselectivity from internal unactivated alkenes.Mechanistic investigations suggest that this transformation proceeds via a NiHhydrogen atom transfer to alkene,followed by a stereoselective fluorine atom transfer process.The weak coordination effect of the tethered amide group is identified as a crucial factor governing the observed regio-and enantioselectivity.展开更多
Electrochemical nitrate reduction(NO_(3)RR)offers a promising avenue for treating nitrate-contaminated water and recovering ammonia(NH_(3)),yet the complexities of direct electron transfer(DET)and hydrogen atom transf...Electrochemical nitrate reduction(NO_(3)RR)offers a promising avenue for treating nitrate-contaminated water and recovering ammonia(NH_(3)),yet the complexities of direct electron transfer(DET)and hydrogen atom transfer(HAT)mechanisms crucial for efficiency remain elusive.This study bridges the gap with a combined experimental and theoretical approach,elucidating the impact of catalyst structure on NO3RR pathways.We discover that catalysts favoring strong NO_(3^(-))adsorption and efficient water dissociation were more inclined towards DET,enhancing denitrification.The Fe@Fe_(3)O_(4)/FF cathode,leveraging the synergistic interplay between metallic Fe and Fe_(3)O_(4),excelled in NO3RR via DET,achieving an NH3yield of 0.28 mmol h-1cm-2and a Faradaic efficiency of 95.7%for NH3at-1.6 V(vs.SCE),with minimal nitrite accumulation at 100 mmol/L nitrate.Conversely,the Fe/FF and Fe_(3)O_(4)/CC cathodes showed reduced NH3production and increased nitrite levels,attributed to the lack of Fe_(3)O_(4)and metallic Fe,respectively,resulting in a dominant HAT mechanism.Moreover,Fe@Fe_(3)O_(4)/FF facilitated complete denitrification in real wastewater treatment by harnessing Cl^(-)for electrochemically mediated breakpoint chlorination.This research not only deepens our understanding of NO3RR mechanisms but also paves the way for designing superior nitrate reduction catalysts.展开更多
The enantioselective separation of racemate,particularly those containing C(sp^(3))-H bonds knowns for their high bond dissociation energies and significant polarity,presents a significant challenge in pharmaceutical ...The enantioselective separation of racemate,particularly those containing C(sp^(3))-H bonds knowns for their high bond dissociation energies and significant polarity,presents a significant challenge in pharmaceutical synthesis.Recent advances have witnessed the fusion of photocatalysis with hydrogen atom transfer(HAT)methodologies,marking a notable trend in synthesis of chiral molecules.This technique uses the excitation of a catalyst to activate substrates,enabling the selective isomerization of chiral centers containing C(sp^(3))configurations.This process distinctively facilitates the direct activation of the C(sp^(3))-H bond in targeted reagents.This review systematically discusses the photocatalytic isomerization of various chiral molecule featuring C(sp^(3))-H centers,capable of undergoing deracemization through two primary HAT mechanisms:direct and indirect pathways.From the perspective of synthetic organic chemistry,this field has progressed towards the development of isomerization strategies for molecules that incorporate an activating group at theα-position adjacent to the C(sp^(3))chiral center.Moreover,it covers methodologies applicable to molecules characterized by specific C-C and C-S bond configurations.The integration of photocatalysis with HAT technology thus provides valuable strategies for the synthesis of enantiopure compounds with enhanced selectivity and efficiency.展开更多
General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two...General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two stations,the geopotential difference between them can be determined.In this study,with the help of two hydrogen atomic clocks(noted as H-masers),using the two-way satellite time and frequency transfer(TWSTFT)technique,we carried out experiments of the geopotential difference determination at the China Aerospace Science&Industry Corporation(CASIC),Beijing.Here the ensemble empirical mode decomposition(EEMD)method is adopted to remove periodic signals included in the original observations.Finally,the clock-comparison-determined geopotential difference in the experiments is determined.Results show that the difference between the geopotential difference determined by GRT and that determined by measuring tape is about 1316.1±931.0 m2s-2,which is equivalent to 134.3±95.0 m in height,and in consistence with the stability of the H-masers applied in the experiments(at the level of10-15/day).With the rapid improvement of atomic clocks’accuracy,the geopotential determination by accurate clocks is prospective,and it is promising to realize the unification of the world vertical height system(WVHS).展开更多
Enones are widely explored in synthetic chemistry as fundamental building blocks for a wide range of reactions and exhibit intriguing biological activities that are pivotal for drug discovery.The development of synthe...Enones are widely explored in synthetic chemistry as fundamental building blocks for a wide range of reactions and exhibit intriguing biological activities that are pivotal for drug discovery.The development of synthetic strategies for highly efficient preparation of enones thereby receives intense attention,in particular through the transition metal-catalyzed coupling reactions.Here,we describe a carbene-catalyzed cross dehydrogenative coupling(CDC)reaction that enables effective assembly of simple aldehydes and alkenes to afford a diverse set of enone derivatives.Mechanistically,the in situ generated aryl radical is pivotal to“activate”the alkene by forming an allyl radical through intermolecular hydrogen atom transfer(HAT)pathway and thus forging the carbon-carbon bond formation with aldehyde as the acyl synthon.Notably,our method represents the first example on the enone synthesis through coupling of“non-functionalized”aldehydes and alkenes as coupling partners,and offers a distinct organocatalytic pathway to the transition metal-catalyzed coupling transformations.展开更多
The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duratio...The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.展开更多
In this work,molecular dynamics modeling was conducted to study hydrogen(H)-induced plastic deformation and cracking of polycrystalα-Fe.Under cyclic loading,the number of vacancies and the stress intensity increase w...In this work,molecular dynamics modeling was conducted to study hydrogen(H)-induced plastic deformation and cracking of polycrystalα-Fe.Under cyclic loading,the number of vacancies and the stress intensity increase with H atom concentration and the number of loading cycles.However,the effect of cyclic loading on cracking is not as significant as the increment of H concentration.As the H concentration increases,the dislocation generation and emission are enhanced in the{110}<111>slip system,but are inhibited in other slip systems.There is a critical H atom concentration,below which the plastic deformation ofα-Fe is facilitated by H atoms.When the critical H concentration is exceeded,the dislocation emission is inhibited by H atoms at grain boundaries,where the H atoms can pin dislocations,causing piling-up of the dislocations to generate a stress concentration.展开更多
In recent years,FeCl_(3)-photocatalyzed direct C–H/Si–H bond functionalization reactions have attracted huge attention.In those transformations,chlorine radical(Cl·)could be generated from FeCl_(3)via a ligandt...In recent years,FeCl_(3)-photocatalyzed direct C–H/Si–H bond functionalization reactions have attracted huge attention.In those transformations,chlorine radical(Cl·)could be generated from FeCl_(3)via a ligandto-metal charge transfer(LMCT)/homolysis process under light irradiation.The resulting chlorine radical subsequently acts as a hydrogen atom transfer(HAT)agent to abstract the hydrogen atom of aliphatic C–H,O–H,or Si–H bonds to give the corresponding C/Si/O-centered radicals for various organic transformations.In this review,we summarized the recent advances in the application of FeCl_(3)as a HAT photocatalyst for the C/Si–H functionalization to construct C–C,C–N,C–Si,C–S,C–B,and C-P bonds.展开更多
The mechanical angular momentum and magnetic moment of the electron and proton spin have been calculated semiclassically with the aid of the uncertainty principle for energy and time. The spin effects of both kinds of...The mechanical angular momentum and magnetic moment of the electron and proton spin have been calculated semiclassically with the aid of the uncertainty principle for energy and time. The spin effects of both kinds of the elementary particles can be expressed in terms of similar formulae. The quantization of the spin motion has been done on the basis of the old quantum theory. It gives a quantum number n = 1/2 as the index of the spin state acceptable for both the electron and proton particle. In effect of the spin existence the electron motion in the hydrogen atom can be represented as a drift motion accomplished in a combined electric and magnetic field. More than 18,000 spin oscillations accompany one drift circulation performed along the lowest orbit of the Bohr atom. The semiclassical theory developed in the paper has been applied to calculate the doublet separation of the experimentally well-examined D line entering the spectrum of the sodium atom. This separation is found to be much similar to that obtained according to the relativistic old quantum theory.展开更多
In 1935,Wigner and Huntington[1]predicted that under extreme compression,molecular hydrogen would dissociate into atomic hydrogen and exhibit metallic properties similar to alkali metals—forming a metallic phase.Sinc...In 1935,Wigner and Huntington[1]predicted that under extreme compression,molecular hydrogen would dissociate into atomic hydrogen and exhibit metallic properties similar to alkali metals—forming a metallic phase.Since then,the pursuit of metallic hydrogen has long been hailed as the“Holy Grail”in the field of high-pressure research.Ninety years have passed,and scientists are still striving to realize this elusive state.Among these efforts,unveiling the process of structural transformation of hydrogen under high pressure is fundamental.展开更多
The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H...The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H- and Zr3O7H- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr2O5- with C2H6, which supports that the observed Zr2O5H- and Zr3O7H- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.展开更多
A general metal-free photochemcial oxidation of benzylic C—H bonds has been successfully accomplished via a hydrogen atom transfer(HAT)process.A range of high value-added aromatic ketones were facilely synthesized wi...A general metal-free photochemcial oxidation of benzylic C—H bonds has been successfully accomplished via a hydrogen atom transfer(HAT)process.A range of high value-added aromatic ketones were facilely synthesized with high chemoselectivity under mild conditions.Moreover,the mild conditions by using air as the oxidant render the developed proto-col more ecofriendly and environmentally sustainable.展开更多
文摘A heat transfer study was conducted,in the framework of Computational Fluid Dynamics(CFD),on a Hot-Wire Chemical Vapour Deposition(HWCVD)reactor chamber to determine a safe deposition distance for atomic hydrogen produced by HWCVD.The objective of this study was to show the feasibility of using heat transfer simulations in determining a safe deposition distance for deposition of this kind.All CFD simulations were set-up and solved within the framework of the CFD packages of OpenFOAM namely;snappyHexMesh for mesh generation,buoyantSimpleFoam and rhoSimpleFoam as the solvers and paraView as the post-processing tool.Using a standard set of deposition parameters for the production of atomic hydrogen by HWCVD,plots of the gas temperature in the deposition region were produced.From these plots,we were able to determine a safe deposition distance in the HWCVD reactor to be in the range between 3 and 4 cm from the filament.
文摘The energy spectrum of the hydrogen atom has been applied in calculating the time rate of energy transitions between the quantum states of the atom. The formal basis of the approach has been provided by the quantum properties of energy and time deduced from the Joule-Lenz law. The rates of the energy transitions obtained in this way were compared with the quantum-mechanical probabilities of transitions calculated earlier by Bethe and Condon and Shortley for the same pairs of the quantum states.
文摘In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.
文摘Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fueling the suspected central superrmassive black hole. Although optical images show a number of violently interacting systems, in many cases the evidence for such interactions is only circumstantial (e.g., asymmetric optical morphologies, projected nearby companion galaxies) or not at all apparent. Here we image quasar host galaxies for the first time in the redshifted 21 cm line emission of neutral atomic hydrogen (HI) gas, which in nearby galaxies has proven to be a particularly sensitive as well as enduring tracer of tidal interactions. The three quasars studied have different optical environments normally seen around low reshift quasars, ranging from a perhaps mildly interacting system to a relatively undisturbed host with a projected neighbouring galaxy to an isolated and apparently serene host galaxy. By contrast with their optical appearences, all three quasar host galaxies exhibit ongoing or remnant tidal HI disruptions tracing galactic encounters or mergers. These observations provide a better understanding of the likely stage of their interaction.
基金Support from National Science Foundation of USA under Grant No. 0630370National Natural Science Foundation of China under Grant Nos. 90403028 and 11074260
文摘We report a theoretical scheme using a B-spline basis set to improve the poor computational accuracy of circular Rydberg states of hydrogen atoms in the intermediate magnetic field. This scheme can produce high accuracy energy levels and valid for an arbitrary magnetic field. Energy levels of hydrogen are presented for circular Rydberg states with azimuthal quantum numbers ｜m｜ =10-70 as a function of magnetic field strengths ranging from zero to 2.35 × 10^9 T. The variation of spatial distributions of electron probability densities with magnetic field strengths is discussed and competition between Coulomb and magnetic interactions is illustrated.
文摘A modified uncertainty principle coupling the intervals of energy and time can lead to the shortest distance attained in course of the excitation process, as well as the shortest possible time interval for that process. These lower bounds are much similar to the interval limits deduced on both the experimental and theoretical footing in the era when the Heisenberg uncertainty principle has been developed. In effect of the bounds existence, a maximal nuclear charge Ze acceptable for the Bohr atomic ion could be calculated. In the next step the velocity of electron transitions between the Bohr orbits is found to be close to the speed of light. This result provides us with the energy spectrum of transitions similar to that obtained in the Bohr’s model. A momentary force acting on the electrons in course of their transitions is estimated to be by many orders larger than a steady electrostatic force existent between the atomic electron and the nucleus.
基金supported by the National Natural Science Foundation of China(grant nos.22206054,U21A20286,and 22478310)the Fundamental Research Funds for the Central China Normal University.
文摘Electrocatalytic nitrate reduction reaction(NO_(3)RR)to ammonia provides a promising approach to environmental preservation and sustainable energy production,but suffers from a low yield rate and poor Faradic efficiency,ascribed to the sluggish active hydrogen(H^(*))generation via water dissociation.Herein,single Ru atoms anchored Co(OH)_(2)(Ru1/Co(OH)_(2))catalysts are synthesized for selective nitrate reduction to ammonia,which exhibits an excellent NH_(3)yield rate of 4200μg h^(-1)cm^(-2)and a high NH_(3)Faradic efficiency of 97%at-0.33 V versus reversible hydrogen electrode,outperforming the counterpart Co(OH)_(2)and the mostly reported electrocatalysts.Experimental and theoretical results reveal that the addition of Ru atoms can boost H^(*)generation and decrease the hydrogenation energy barrier on Ru1/Co(OH)_(2),leading to enhanced NO_(3)RR performance.An integrated system of electrochemical NO_(3)RR electrolyzer and in-situ NH_(3)recovery is present,where the electrochemical NO_(3)RR can be coupled with a hydrazine oxidation reaction to achieve a more highly efficient and electricity-saving system for NH_(3)recovery.This work provides guidance for the rational design of high-performance NO_(3)RR electrocatalysts by the effective regulation of H^(*)generation and holds great promise for simultaneous nitrate-containing wastewater treatment and resource recovery.
基金supported by the National Natural Science Foundation of China(Nos.U22A20402,U21A20286,and 22102100)the Key Program of Shenzhen Science and Technology Commission(No.JCYJ20220818095601002)the Natural Science Foundation of Shanghai(No.22ZR1431700).
文摘Atomic hydrogen(H∗)plays a crucial role in electrochemical reduction technology towards various environmental and energy applications,but suffers from low utilization efficiency arisen from the undesirable H-H dimerization and the competitive adsorption between water molecule with reactants on the traditional adjacent catalytic sites.Herein,we anchored Pd single atoms on the naturally formed titanium oxide of titanium foam to construct Pd_(1)-O-Ti dual-site electrocatalyst with spatially isolated water dissociation and H∗utilization site,which synchronously inhibits the H-H dimerization and the competitive adsorption of water molecule and targeted reactants.Experiments and theoretical calculations revealed that the Ti-O sites could synergistically dissociate water to H∗,which overflowed to nearby Pd single-atom sites for designed reduction reactions and utilization benefiting from the hydrogen spillover ability of titanium oxide substrate.These Pd_(1)-O-Ti dual sites delivered almost 100%bromate reduction efficiency with a rate constant of 1.57 h^(-1),far superior to those of Pdn-O-Ti with adjacent Pd sites(0.52 h^(-1)),Pd_(1)-N-C with single sites(0.04 h^(-1))and commercial Pd/C(0.18 h^(-1)),respectively.This study sheds light on the importance of integrating synergistic active sites for complicated electrochemical reactions,and provide new insights in improving H∗ utilization for environmental remediation.
基金This research was made possible as a result of a generous grant from the Fundamental Research Funds for the Central Universities(Nos.2232024Y-01,2232024A-03)the National Science Fund for Excellent Young Scholars(No.22122101).
文摘Here we present a highly efficient protocol utilizing nickel-hydride hydrogen atom transfer catalysis for the regio-and enantioselective hydrofluorination of internal alkenes.This method efficiently assembles a wide array of enantioenrichedβ-fluoro amides with excellent regio-and enantioselectivity from internal unactivated alkenes.Mechanistic investigations suggest that this transformation proceeds via a NiHhydrogen atom transfer to alkene,followed by a stereoselective fluorine atom transfer process.The weak coordination effect of the tethered amide group is identified as a crucial factor governing the observed regio-and enantioselectivity.
基金support from the National Natural Science Foundation of China(Nos.U21A2034 and 21876052)the Guangdong Special Support Plan for Innovation Teams(No.2019BT02L218)+1 种基金the Guangdong Special Support Plan for Young Top-notch Talents(No.2019TQ05L179)the Natural Science Foundation of Guangdong Province,China(No.2021B1515120077)。
文摘Electrochemical nitrate reduction(NO_(3)RR)offers a promising avenue for treating nitrate-contaminated water and recovering ammonia(NH_(3)),yet the complexities of direct electron transfer(DET)and hydrogen atom transfer(HAT)mechanisms crucial for efficiency remain elusive.This study bridges the gap with a combined experimental and theoretical approach,elucidating the impact of catalyst structure on NO3RR pathways.We discover that catalysts favoring strong NO_(3^(-))adsorption and efficient water dissociation were more inclined towards DET,enhancing denitrification.The Fe@Fe_(3)O_(4)/FF cathode,leveraging the synergistic interplay between metallic Fe and Fe_(3)O_(4),excelled in NO3RR via DET,achieving an NH3yield of 0.28 mmol h-1cm-2and a Faradaic efficiency of 95.7%for NH3at-1.6 V(vs.SCE),with minimal nitrite accumulation at 100 mmol/L nitrate.Conversely,the Fe/FF and Fe_(3)O_(4)/CC cathodes showed reduced NH3production and increased nitrite levels,attributed to the lack of Fe_(3)O_(4)and metallic Fe,respectively,resulting in a dominant HAT mechanism.Moreover,Fe@Fe_(3)O_(4)/FF facilitated complete denitrification in real wastewater treatment by harnessing Cl^(-)for electrochemically mediated breakpoint chlorination.This research not only deepens our understanding of NO3RR mechanisms but also paves the way for designing superior nitrate reduction catalysts.
基金the National Natural Science Foundation of China(No.22072020)the Science Foundation of the Fujian Province(Nos.2022HZ027004,2022L3082,2021L3003,and 2019 J01203).
文摘The enantioselective separation of racemate,particularly those containing C(sp^(3))-H bonds knowns for their high bond dissociation energies and significant polarity,presents a significant challenge in pharmaceutical synthesis.Recent advances have witnessed the fusion of photocatalysis with hydrogen atom transfer(HAT)methodologies,marking a notable trend in synthesis of chiral molecules.This technique uses the excitation of a catalyst to activate substrates,enabling the selective isomerization of chiral centers containing C(sp^(3))configurations.This process distinctively facilitates the direct activation of the C(sp^(3))-H bond in targeted reagents.This review systematically discusses the photocatalytic isomerization of various chiral molecule featuring C(sp^(3))-H centers,capable of undergoing deracemization through two primary HAT mechanisms:direct and indirect pathways.From the perspective of synthetic organic chemistry,this field has progressed towards the development of isomerization strategies for molecules that incorporate an activating group at theα-position adjacent to the C(sp^(3))chiral center.Moreover,it covers methodologies applicable to molecules characterized by specific C-C and C-S bond configurations.The integration of photocatalysis with HAT technology thus provides valuable strategies for the synthesis of enantiopure compounds with enhanced selectivity and efficiency.
基金supported by National Natural Science Foundation of China(NSFC)(grant Nos.41721003,41631072,41874023,41804012,41429401,41574007)Natural Science Foundation of Hubei Province(grant No.2019CFB611)
文摘General relativity theory(GRT)concludes that a precise clock ticks at different running rates if it is under the influence of different geopotentials.Therefore,by comparing the running rates of clocks at arbitrary two stations,the geopotential difference between them can be determined.In this study,with the help of two hydrogen atomic clocks(noted as H-masers),using the two-way satellite time and frequency transfer(TWSTFT)technique,we carried out experiments of the geopotential difference determination at the China Aerospace Science&Industry Corporation(CASIC),Beijing.Here the ensemble empirical mode decomposition(EEMD)method is adopted to remove periodic signals included in the original observations.Finally,the clock-comparison-determined geopotential difference in the experiments is determined.Results show that the difference between the geopotential difference determined by GRT and that determined by measuring tape is about 1316.1±931.0 m2s-2,which is equivalent to 134.3±95.0 m in height,and in consistence with the stability of the H-masers applied in the experiments(at the level of10-15/day).With the rapid improvement of atomic clocks’accuracy,the geopotential determination by accurate clocks is prospective,and it is promising to realize the unification of the world vertical height system(WVHS).
基金funding supports from the National Natural Science Foundation of China(Nos.21732002,22061007,22071036,and 22207022)Frontiers Science Center for Asymmetric Synthesis and Medicinal Molecules,National Natural Science Fund for Excellent Young Scientists Fund Program(Overseas),the starting grant of Guizhou University[No.(2022)47)]+10 种基金Department of Education,Guizhou Province[Qianjiaohe KY No.(2020)004]The 10 Talent Plan(Shicengci)of Guizhou Province(No.[2016]5649)Science and Technology Department of Guizhou Province(Nos.[Qiankehe-jichu-ZK[2022]zhongdian024],[2018]2802,[2019]1020,QKHJC-ZK[2022]-455)Department of Education of Guizhou Province(No.QJJ(2022)205)Program of Introducing Talents of Discipline to Universities of China(111 Program,No.D20023)at Guizhou UniversitySingapore National Research Foundation under its NRF Investigatorship(No.NRF-NRFI2016–06)Competitive Research Program(No.NRF-CRP22–2019–0002)Ministry of Education,Singapore,under its MOE Ac RF Tier 1 Award(Nos.RG7/20,RG70/21)MOE AcRF Tier 2(No.MOE2019-T2–2–117)MOE AcRF Tier 3 Award(No.MOE2018-T3–1–003)a Chair Professorship Grant,and Nanyang Technological University。
文摘Enones are widely explored in synthetic chemistry as fundamental building blocks for a wide range of reactions and exhibit intriguing biological activities that are pivotal for drug discovery.The development of synthetic strategies for highly efficient preparation of enones thereby receives intense attention,in particular through the transition metal-catalyzed coupling reactions.Here,we describe a carbene-catalyzed cross dehydrogenative coupling(CDC)reaction that enables effective assembly of simple aldehydes and alkenes to afford a diverse set of enone derivatives.Mechanistically,the in situ generated aryl radical is pivotal to“activate”the alkene by forming an allyl radical through intermolecular hydrogen atom transfer(HAT)pathway and thus forging the carbon-carbon bond formation with aldehyde as the acyl synthon.Notably,our method represents the first example on the enone synthesis through coupling of“non-functionalized”aldehydes and alkenes as coupling partners,and offers a distinct organocatalytic pathway to the transition metal-catalyzed coupling transformations.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10575046 and 10775062)
文摘The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.
基金supported by National Natural Science Foundation of China(Nos.52374072,No.52004323)CNPC Innovation Foundation(No.2022DQ02-0502)+1 种基金Natural Science Foundation of Shandong Province(Nos.ZR2020ME094,ZR2019BEE006 and ZR2019MEE108)the Senior Foreign Expert Project Fund(No.G2022152003L).
文摘In this work,molecular dynamics modeling was conducted to study hydrogen(H)-induced plastic deformation and cracking of polycrystalα-Fe.Under cyclic loading,the number of vacancies and the stress intensity increase with H atom concentration and the number of loading cycles.However,the effect of cyclic loading on cracking is not as significant as the increment of H concentration.As the H concentration increases,the dislocation generation and emission are enhanced in the{110}<111>slip system,but are inhibited in other slip systems.There is a critical H atom concentration,below which the plastic deformation ofα-Fe is facilitated by H atoms.When the critical H concentration is exceeded,the dislocation emission is inhibited by H atoms at grain boundaries,where the H atoms can pin dislocations,causing piling-up of the dislocations to generate a stress concentration.
基金the National Natural Science Foundation of China(Nos.21971224,22171249)Program for Science&Technology Innovation Talents in Universities of Henan Province(No.23HASTIT003).
文摘In recent years,FeCl_(3)-photocatalyzed direct C–H/Si–H bond functionalization reactions have attracted huge attention.In those transformations,chlorine radical(Cl·)could be generated from FeCl_(3)via a ligandto-metal charge transfer(LMCT)/homolysis process under light irradiation.The resulting chlorine radical subsequently acts as a hydrogen atom transfer(HAT)agent to abstract the hydrogen atom of aliphatic C–H,O–H,or Si–H bonds to give the corresponding C/Si/O-centered radicals for various organic transformations.In this review,we summarized the recent advances in the application of FeCl_(3)as a HAT photocatalyst for the C/Si–H functionalization to construct C–C,C–N,C–Si,C–S,C–B,and C-P bonds.
文摘The mechanical angular momentum and magnetic moment of the electron and proton spin have been calculated semiclassically with the aid of the uncertainty principle for energy and time. The spin effects of both kinds of the elementary particles can be expressed in terms of similar formulae. The quantization of the spin motion has been done on the basis of the old quantum theory. It gives a quantum number n = 1/2 as the index of the spin state acceptable for both the electron and proton particle. In effect of the spin existence the electron motion in the hydrogen atom can be represented as a drift motion accomplished in a combined electric and magnetic field. More than 18,000 spin oscillations accompany one drift circulation performed along the lowest orbit of the Bohr atom. The semiclassical theory developed in the paper has been applied to calculate the doublet separation of the experimentally well-examined D line entering the spectrum of the sodium atom. This separation is found to be much similar to that obtained according to the relativistic old quantum theory.
文摘In 1935,Wigner and Huntington[1]predicted that under extreme compression,molecular hydrogen would dissociate into atomic hydrogen and exhibit metallic properties similar to alkali metals—forming a metallic phase.Since then,the pursuit of metallic hydrogen has long been hailed as the“Holy Grail”in the field of high-pressure research.Ninety years have passed,and scientists are still striving to realize this elusive state.Among these efforts,unveiling the process of structural transformation of hydrogen under high pressure is fundamental.
基金This work was supported by the Chinese Academy of Sciences （Hundred Talents Fund）, the National Natural Science Foundation of China （No.20703048 and No.20803083）, and the Center of Molecular Science Foundation of Institute of Chemistry, Chinese Academy of Sciences （No.CMS-LX200902）.
文摘The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H- and Zr3O7H- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr2O5- with C2H6, which supports that the observed Zr2O5H- and Zr3O7H- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.
文摘A general metal-free photochemcial oxidation of benzylic C—H bonds has been successfully accomplished via a hydrogen atom transfer(HAT)process.A range of high value-added aromatic ketones were facilely synthesized with high chemoselectivity under mild conditions.Moreover,the mild conditions by using air as the oxidant render the developed proto-col more ecofriendly and environmentally sustainable.
