Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ra...Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.展开更多
We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affiniti...We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affinities of PB and AsB are measured to be 2.751(1)and 2.600(1)eV,respectively.The ground states of the PB^(−)and AsB−anions are determined to be ^(2)Σ^(+) with a σ^(1)π^(4) valence electron configuration.The ground states of neutral PB and AsB are found to be ^(3)Π_(2) with a σ^(1)π^(3) electron configuration.The spin-orbit excited states(^(3)Π_(1) and ^(3)Π_(0)),as well as two low-lying singlet excited states(^(1)Σ^(+)and ^(1)Π),are observed.Unusual spectroscopic characteristics are observed in the ^(3)Π_(2) ground state of AsB,probably due to state mixing with a higher-lying ^(1)Δ_(2) state.The current work provides extensive electronic and spectroscopic information for the PB and AsB molecules.展开更多
High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The...High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The highly structured spectra were compared with results from DFT calculations to determine the dominant structure to be cis-CH_(3)OTi(O)OH^(−),a dissociative adduct in which CH3OH is split by TiO_(2)^(−).The experiment yields an electron affinity of 1.2152(7)eV for TiO_(2)CH^(3)OH as well as several vibrational frequencies for the neutral species.Comparison to Franck−Condon(FC)simulations shows that while most experimental features appear in the simulations,several are not and are assigned to FC-forbidden transitions involving non-totally symmetric vibrational modes.The FC-allowed and forbidden transi-tions also exhibit different photoelectron angular distributions.The FC-forbidden transitions are attributed to Herzberg−Teller(HT)coupling with the A^(2)A″excited state of the anion.The results are compared to previous cryogenic slow electron velocity-map imaging(cryo-SE-Ⅵ)studies of bare TiO_(2)^(−)and the water-split adduct TiO_(3)H_(2)^(−).展开更多
The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment ene...The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment energy of Co_(2)Ge_(10)^(-)was measured to be 2.86±0.08 eV.The lowest-energy isomer of Co_(2)Ge_(10)^(-)is in a doublet state and has a cage-like structure with Cs symmetry,which can be constructed by a tetragonal bipyramid on top of a pentagonal bipyramid and these two bipyramid structures share a common Co atom.The most stable structure of neutral Co_(2)Ge_(10)resembles its anionic counterpart and it is in a triplet state.The natural population analysis showed that the inner Co atom of both the anionic and neutral Co_(2)Ge_(10)acquires negative charge from the neighboring Ge atoms.The outer Co atom has a larger spin moment than the inner Co atom,indicating that the magnetic moments of Co_(2)Ge_(10)^(-/0)are mainly contributed by the outer Co atom.Analyses of the density of states and molecular orbitals indicated that there are a few highly delocalized molecular orbitals in Co_(2)Ge_(10)^(-),which are mainly contributed by Ge 4s atomic orbitals.展开更多
MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy t...MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy to support essential biological functions.To understand the structure and stabilization mechanism of MgATP,we conducted a joint negative ion photoelectron spectroscopic and computational study of the[ATP^(4-)·Mg^(2+)]^(2-)complex dianion,using[ATP^(4-)·2H^(+)]^(2-)as a reference.The experimentally determined adiabatic and vertical detachment energies(ADE and VDE)of[ATP^(4-)·Mg^(2+)]^(2-)at 20 K are 3.51±0.05 eV and 3.82±0.05 eV,respectively.The major spectral features of[ATP^(4-)·Mg^(2+)]^(2-)are attributed to two theoretically identified isomers with unfolded geometries,which are stabilized primarily by electrostatic interactions between Mg^(2+)and the triphosphate and ribose groups,with four deprotonated oxygens forming a pseudo-tetrahedral coordination.In contrast,[ATP^(4-)·2H^(+)]^(2-)exhibits a fundamentally different stabilization mechanism.Although most of the fifteen identified[ATP^(4-)·2H^(+)]^(2-)isomers also adopt unfolded geometries,they are primarily stabilized by intramolecular hydrogen bonds within the triphosphate group and between triphosphate and ribose groups.The interaction between ATP^(4-)and two protons is found to be much weaker than that with Mg^(2+),and[ATP^(4-)·2H^(+)]^(2-)exhibits substantial structural flexibility compared to[ATP^(4-)·Mg^(2+)]^(2-)due to the conformational constraint of the triphosphate chain by Mg^(2+).Thirteen[ATP^(4-)·2H^(+)]^(2-)isomers with unfolded geometries likely account for the major high-EBE(electron-binding-energy)spectral features.Notably,for the first time,a low EBE and temperature-dependent spectral feature is observed and attributed to two folded isomers of[ATP^(4-)·2H^(+)]^(2-),which exist at 20 K but disappear at room temperature.This study provides valuable molecular-level insights into cellular MgATP that resides within the hydrophobic pockets of proteins.展开更多
The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(...The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(2)(M=Ti,Zr,and Hf)compounds are formed in bent insertion structures.The observed ground-state adiabatic detachment energy(ADE)is measured to be 1.597±0.003,1.651±0.003,and 2.119±0.003 eV for TiO_(2)^(-),ZrO_(2)^(-),and HfO_(2)^(-),respectively.The vibrational frequencies of the anionic and neutral MO_(2)are also determined from the experimental spectra.The results of theoretical calculations show that the electronic configurations of MO_(2)^(-)are^(2)A_(1)with C_(2v)point group.Bond order analysis indicates that the two M-O bonds are all multiple characters.展开更多
The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectros...The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectroscopy(XPS)is designed here to accurately characterize the chemical and structural differences between different QDs.This method enables the determination of the reason for the minimal differences between the optical properties of different QDs depending on the synthesis process,which is difficult to determine using conventional methods alone.Combined with model simulations,the XPS spectra obtained at different photon energies reveal the internal structures and chemical-state distributions of the QDs.In particular,the QD synthesized under optimal conditions demonstrates a relatively lower degree of oxidation of the core and more uniformly stacked ZnSe/ZnS shell layers.The internal structures and chemical-state distributions of QDs are closely related to their optical properties.Finally,the synchrotron-based XPS proposed here can be applied to compare nearly equivalent QDs with slightly different optical properties.展开更多
A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-lar...A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-larly crosses the master supersonic jet beam from a home-made pulsed piezo valve.The discharge nozzle is designed for high voltage gas discharge with efficient metal sputtering of the cathode,and thus plays a role in met-al atom and ion source.Supersonically jet-cooled anions can be produced in the master gas jet via reactions of the plasma products.The source is integrated into a photoelectron ve-locity imaging spectrometer.Test mass spectrometry experiments show that the ion source can efficiently produce transition metal containing anions,such as FeO_(m)^(-),CuO_(m)^(-),CuC_(n)^(-),CuC_(n)O_(m)^(-).The photoelectron imaging results by photodetachment of O-show that the pho-toelectron energy resolution of the whole instrument isΔE/E≈2.3%,and the results of FeO^(-)indicate that internal temperatures of anions from the source could be efficiently cooled down.展开更多
We have developed a compact photoelectron imaging facility, including an anion source with dissociative photoelectron attachment to molecules, a linear time-of-flight mass spec-trometry （TOFMS）, and an orthogonal hi...We have developed a compact photoelectron imaging facility, including an anion source with dissociative photoelectron attachment to molecules, a linear time-of-flight mass spec-trometry （TOFMS）, and an orthogonal high-resolution threshold photoelectron velocity map imaging spectrometer （VMI）. Intense and cold cluster anions were prepared in photoelectron- attachment processes upon pulsed UV laser ablation of metal target. Combining this anion source with TOFMS-VMI, the achieved mass resolution is about 200, and the electron ki- netic energy resolution is better than 3%, i.e., 30 meV for 1 eV electrons. More importantly, low-energy photoelectron imaging spectra for CH3S- and S2- at 611.46 nm are obtained. In both cases, the refined electron affinities are determined to be 1.86264-0.0020 eV for CH3S and 1.67444-0.0035 eV for S2, respectively. Preliminary results suggest that the apparatus is a powerful tool for estimating precise electron affinities values from threshold photoelectron imaging spectroscopy.展开更多
The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm ...The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.展开更多
The wavelength dependence of photoelectron angular distributions （PADs） of two-photon detachment of Cu^- has been directly studied by using the photoelectron map imaging. Results show that for the laser field intens...The wavelength dependence of photoelectron angular distributions （PADs） of two-photon detachment of Cu^- has been directly studied by using the photoelectron map imaging. Results show that for the laser field intensity of 6.0×10^10W/cm^2, PADs exhibit dramatic change with the external field wavelength. Comparison between the experimental observation and the lowest-order perturbation theory prediction indicates that the pattern of PADs can be explained by the interference of the s and d partial waves in the final state. Relative contri- butions of s and d partial waves in the two-photon detachment at different laser wavelengths are obtained.展开更多
By developing a full quantum scattering theory of high-order above-threshold ionization,we study the energy spectra and the angular distributions of photoelectrons from atoms with intense laser fields shining on them....By developing a full quantum scattering theory of high-order above-threshold ionization,we study the energy spectra and the angular distributions of photoelectrons from atoms with intense laser fields shining on them.We find that real rescattering can occur many times,and even infinite times.The photoelectrons from the rescattering process form a broad plateau in the kinetic-energy spectrum.We further disclose a multiple-plateau structure formed by the high-energy photoelectrons,which absorb many photons during the rescattering process.Moreover,we find that both the angular distributions and the kinetic-energy spectra of photoelectrons obey the same scaling law as that for directly emitted photoelectrons.展开更多
We investigated the structural evolution and elecfronic properties of ConC3-/0 and ConC4-/0 （n=1-4） clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabati...We investigated the structural evolution and elecfronic properties of ConC3-/0 and ConC4-/0 （n=1-4） clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of CO1-4C3- and COl-4C4- were obtained from their photoelectron spectra. By comparing the theoretical results with the experimental data, the global minimum structures were determined. The results indicate that the carbon atoms of ConC3-/0 and ConC4-/0 （n=1-4） are separated from each other gradually with increasing number of cobalt atoms but a C2 unit still remains at n=4. It is interesting that the Co2C3- and Co2C4- anions have planar structures whereas the neutral Co2C3 and Co2C4 have linear structures with the Co atoms at two ends. The Co3C3- anion has a planar structure with a Co2C2 four-membered ring and a Co3C four-membered ring sharing a Co-Co bond, while the neutral Co3C3 is a three-dimensional structure with a C2 unit and a C atom connecting to two faces of the Co3 triangle.展开更多
The AgOCH3- and Ag-（CH3OH）x（x=l, 2） anions are studied by photoelectron imaging as well as ab initio calculations. The adiabatic and vertical detachment energies （ADE and VDE） of AgOCH3- are determined as 1.29（...The AgOCH3- and Ag-（CH3OH）x（x=l, 2） anions are studied by photoelectron imaging as well as ab initio calculations. The adiabatic and vertical detachment energies （ADE and VDE） of AgOCH3- are determined as 1.29（2） and 1.34（2） eV, respectively, from the vibrational resolved photoelectron spectrum. The Ag-（CH3OH）l,2 anionic complexes are characterized as metal atomic anion solvated by the CH3OH molecules with the electron mainly localized on the metal. The photoelectron spectra of Ag-（CH3OH）x （x=O, 1, 2） show a gradual increase in VDE with increasing x, due to the solvent stabilization. Evidence for the methanol-methanol hydrogen bonding interactions appears when the Ag- is solvated by two methanol molecules.展开更多
The growth pattern and electronic properties of TiGen^- （n=7-12） clusters were investigated using anion photoelectron spectroscopy and density functional theory calculations. For both anionic and neutral TiGen clust...The growth pattern and electronic properties of TiGen^- （n=7-12） clusters were investigated using anion photoelectron spectroscopy and density functional theory calculations. For both anionic and neutral TiGen clusters, a half-encapsulated boat-shaped structure appears at n=8, and the boat-shaped structure is gradually covered by the additional Ge atoms to form Gen cage at n=9-11. TiGe12^- cluster has a distorted hexagonal prism cage structure. According to the natural population analysis, the electron transfers from the Gen framework to the Ti atom for TiGen^-/0 clusters at n=8-12, implying that the electron transfer pattern is related to the structural evolution.展开更多
Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the vale...Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO2, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO2（110） surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO2 substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytie process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.展开更多
We investigate Autler-Townes splitting in the photoelectron spectra of K2 molecule driven by pump-probe pulses via employing the time-dependent wave packet approach. It is found that the magnitude of Aulter-Townes spl...We investigate Autler-Townes splitting in the photoelectron spectra of K2 molecule driven by pump-probe pulses via employing the time-dependent wave packet approach. It is found that the magnitude of Aulter-Townes splitting varies with the wavelength of the intense laser pulse. In particular, the phenomenon of Aulter-Townes splitting vanishes for the far-off resonance of the pump pulse. Also, the split peaks of Autler Townes in the case of resonant pump pulse give us an approach to directly obtaining the transition dipole moment of a molecule.展开更多
We present photoelectron angular distribution of the aligned molecular ion H2^＋ by intense ultrashort attosecond extreme ultraviolet laser pulses from numerical solutions of timedependent Schrodinger equations. Photo...We present photoelectron angular distribution of the aligned molecular ion H2^＋ by intense ultrashort attosecond extreme ultraviolet laser pulses from numerical solutions of timedependent Schrodinger equations. Photoionization from a superposition state of the ground 1sσg and the excited 2pσu states with pulses at photon energies above the ionization potential, hω〉Ip, and intensity 10^14 W/cm^2, yields pulse duration dependent asymmetry of photoelectron angular distributions. We attribute the asymmetry to the periodical oscillation of the coherent electron wave packets, resulting from the interference of the two electronic states. For the processes with long pulse durations, such duration dependence is absent and symmetric angular distributions are obtained.展开更多
We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse...We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_(1/2) and 5P_(3/2) in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.展开更多
An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is chara...An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.展开更多
基金supported by the Vinnova(project number 2020-03778)supported by the Swedish Research Council(Vetenskapsradet,project number 2021-04157).
文摘Nano-scale chemical inhomogeneity in surface oxide films formed on a V-and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron-based hard X-ray Photoelectron emission spectroscopy(HAXPES)and microscopy(HAXPEEM)as well as microscopic X-ray absorption spectroscopy(μ-XAS)techniques.The results reveal the inhomogeneity in the oxide films on the micron-sized Cr_(2)N-and VN-type particles,while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600℃.The oxide film formed on Cr_(2)N-type particles is rich in Cr_(2)O_(3) compared with that on the martensite matrix and VN-type particles.With the increase of tempering temperature,Cr_(2)O_(3) formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.
基金supported by the National Science Foundation (Grant No.CHE-2403841)。
文摘We report a study on the electronic structure and chemical bonding of the PB and AsB diatomic molecules using high-resolution photoelectron imaging of cryogenically-cooled PB^(−)and AsB^(−)anions.The electron affinities of PB and AsB are measured to be 2.751(1)and 2.600(1)eV,respectively.The ground states of the PB^(−)and AsB−anions are determined to be ^(2)Σ^(+) with a σ^(1)π^(4) valence electron configuration.The ground states of neutral PB and AsB are found to be ^(3)Π_(2) with a σ^(1)π^(3) electron configuration.The spin-orbit excited states(^(3)Π_(1) and ^(3)Π_(0)),as well as two low-lying singlet excited states(^(1)Σ^(+)and ^(1)Π),are observed.Unusual spectroscopic characteristics are observed in the ^(3)Π_(2) ground state of AsB,probably due to state mixing with a higher-lying ^(1)Δ_(2) state.The current work provides extensive electronic and spectroscopic information for the PB and AsB molecules.
基金funded by the Air Force Office of Scientific Research (AFOSR) under Grant (No.FA955023-1-0545)。
文摘High-resolution photoelectron spectra of cryogenically cooled TiO_(2)CH_(3)OH^(−)anions obtained with slow electron velocity-map imaging are reported and used to explore the reactions of TiO_(2)^(−/0)with methanol.The highly structured spectra were compared with results from DFT calculations to determine the dominant structure to be cis-CH_(3)OTi(O)OH^(−),a dissociative adduct in which CH3OH is split by TiO_(2)^(−).The experiment yields an electron affinity of 1.2152(7)eV for TiO_(2)CH^(3)OH as well as several vibrational frequencies for the neutral species.Comparison to Franck−Condon(FC)simulations shows that while most experimental features appear in the simulations,several are not and are assigned to FC-forbidden transitions involving non-totally symmetric vibrational modes.The FC-allowed and forbidden transi-tions also exhibit different photoelectron angular distributions.The FC-forbidden transitions are attributed to Herzberg−Teller(HT)coupling with the A^(2)A″excited state of the anion.The results are compared to previous cryogenic slow electron velocity-map imaging(cryo-SE-Ⅵ)studies of bare TiO_(2)^(−)and the water-split adduct TiO_(3)H_(2)^(−).
基金supported by the National Natural Science Foundation of China(Nos.92461313,12074387,and 92161114)the Innovation Capability Support Program of Shaanxi Province(No.2023-CX-TD-49).
文摘The structure and electronic properties of Co_(2)Ge_(10)^(-)anion and its neutral counterpart were investigated by anion photoelectron spectroscopy and theoretical calculations.The experimental vertical detachment energy of Co_(2)Ge_(10)^(-)was measured to be 2.86±0.08 eV.The lowest-energy isomer of Co_(2)Ge_(10)^(-)is in a doublet state and has a cage-like structure with Cs symmetry,which can be constructed by a tetragonal bipyramid on top of a pentagonal bipyramid and these two bipyramid structures share a common Co atom.The most stable structure of neutral Co_(2)Ge_(10)resembles its anionic counterpart and it is in a triplet state.The natural population analysis showed that the inner Co atom of both the anionic and neutral Co_(2)Ge_(10)acquires negative charge from the neighboring Ge atoms.The outer Co atom has a larger spin moment than the inner Co atom,indicating that the magnetic moments of Co_(2)Ge_(10)^(-/0)are mainly contributed by the outer Co atom.Analyses of the density of states and molecular orbitals indicated that there are a few highly delocalized molecular orbitals in Co_(2)Ge_(10)^(-),which are mainly contributed by Ge 4s atomic orbitals.
基金was supported by the U.S.Department of Energy(DOE),Office of Science,Office of Basic Energy Sciences,Division of Chemical Sciences,Geosciences,and Biosciences,Condensed Phase and Interfacial Molecular Science program,FWP 16248.
文摘MgATP is a stable complex formed by the chelation of Mg^(2+)with deprotonated adenosine-5'-triphosphate(ATP).In the cellular environment,MgATP plays a critical role in ATP hydrolysis,releasing substantial energy to support essential biological functions.To understand the structure and stabilization mechanism of MgATP,we conducted a joint negative ion photoelectron spectroscopic and computational study of the[ATP^(4-)·Mg^(2+)]^(2-)complex dianion,using[ATP^(4-)·2H^(+)]^(2-)as a reference.The experimentally determined adiabatic and vertical detachment energies(ADE and VDE)of[ATP^(4-)·Mg^(2+)]^(2-)at 20 K are 3.51±0.05 eV and 3.82±0.05 eV,respectively.The major spectral features of[ATP^(4-)·Mg^(2+)]^(2-)are attributed to two theoretically identified isomers with unfolded geometries,which are stabilized primarily by electrostatic interactions between Mg^(2+)and the triphosphate and ribose groups,with four deprotonated oxygens forming a pseudo-tetrahedral coordination.In contrast,[ATP^(4-)·2H^(+)]^(2-)exhibits a fundamentally different stabilization mechanism.Although most of the fifteen identified[ATP^(4-)·2H^(+)]^(2-)isomers also adopt unfolded geometries,they are primarily stabilized by intramolecular hydrogen bonds within the triphosphate group and between triphosphate and ribose groups.The interaction between ATP^(4-)and two protons is found to be much weaker than that with Mg^(2+),and[ATP^(4-)·2H^(+)]^(2-)exhibits substantial structural flexibility compared to[ATP^(4-)·Mg^(2+)]^(2-)due to the conformational constraint of the triphosphate chain by Mg^(2+).Thirteen[ATP^(4-)·2H^(+)]^(2-)isomers with unfolded geometries likely account for the major high-EBE(electron-binding-energy)spectral features.Notably,for the first time,a low EBE and temperature-dependent spectral feature is observed and attributed to two folded isomers of[ATP^(4-)·2H^(+)]^(2-),which exist at 20 K but disappear at room temperature.This study provides valuable molecular-level insights into cellular MgATP that resides within the hydrophobic pockets of proteins.
基金supported by the National Natural Science Foundation of China(No.22273065)Shandong Energy institute(SEI U202312)"Strategic Priority Research Program"of the Chinese Academy of Sciences(No.XDA02020000).
文摘The vibrational resolved spectra of MO_(2)^(-)/MO_(2)(M=Ti,Zr,and Hf)are reported by using photoelectron imaging and theoretical calculations.The results indicate that all the ground states of anionic and neutral MO_(2)(M=Ti,Zr,and Hf)compounds are formed in bent insertion structures.The observed ground-state adiabatic detachment energy(ADE)is measured to be 1.597±0.003,1.651±0.003,and 2.119±0.003 eV for TiO_(2)^(-),ZrO_(2)^(-),and HfO_(2)^(-),respectively.The vibrational frequencies of the anionic and neutral MO_(2)are also determined from the experimental spectra.The results of theoretical calculations show that the electronic configurations of MO_(2)^(-)are^(2)A_(1)with C_(2v)point group.Bond order analysis indicates that the two M-O bonds are all multiple characters.
基金Advanced Light Source,which is a DOE Office of Science User Facility under contract no.DE-AC02-05CH11231the Basque Government for funding through a PhD Fellowship(Grant no.PRE_2018_2_0285)+1 种基金through Egonlabur Travel Fellowship(Grant no.EP_2018_1_0004)partially supported by an Early Career Award in the Condensed Phase and Interfacial Molecular Science Program,in the Chemical Sciences Geosciences and Biosciences Division of the Office of Basic Energy Sciences of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231.
文摘The development of an analytical method for determining the properties of quantum dots(QDs)is crucial for improving the optical performance of QD-based displays.Therefore,synchrotron-based X-ray photoelectron spectroscopy(XPS)is designed here to accurately characterize the chemical and structural differences between different QDs.This method enables the determination of the reason for the minimal differences between the optical properties of different QDs depending on the synthesis process,which is difficult to determine using conventional methods alone.Combined with model simulations,the XPS spectra obtained at different photon energies reveal the internal structures and chemical-state distributions of the QDs.In particular,the QD synthesized under optimal conditions demonstrates a relatively lower degree of oxidation of the core and more uniformly stacked ZnSe/ZnS shell layers.The internal structures and chemical-state distributions of QDs are closely related to their optical properties.Finally,the synchrotron-based XPS proposed here can be applied to compare nearly equivalent QDs with slightly different optical properties.
基金supports from the National Natural Science Foundation of China(No.22173089,No.21827804,and No.22103075)the National Key R&D Program of China(No.2021YFA0716801 and No.2017YFA0303502).
文摘A plasma injection ion source has been de-veloped for the photoelectron velocity imag-ing studies of metal-containing anions.The source employs a pulse discharge nozzle for generating a plasma beam that perpendicu-larly crosses the master supersonic jet beam from a home-made pulsed piezo valve.The discharge nozzle is designed for high voltage gas discharge with efficient metal sputtering of the cathode,and thus plays a role in met-al atom and ion source.Supersonically jet-cooled anions can be produced in the master gas jet via reactions of the plasma products.The source is integrated into a photoelectron ve-locity imaging spectrometer.Test mass spectrometry experiments show that the ion source can efficiently produce transition metal containing anions,such as FeO_(m)^(-),CuO_(m)^(-),CuC_(n)^(-),CuC_(n)O_(m)^(-).The photoelectron imaging results by photodetachment of O-show that the pho-toelectron energy resolution of the whole instrument isΔE/E≈2.3%,and the results of FeO^(-)indicate that internal temperatures of anions from the source could be efficiently cooled down.
文摘We have developed a compact photoelectron imaging facility, including an anion source with dissociative photoelectron attachment to molecules, a linear time-of-flight mass spec-trometry （TOFMS）, and an orthogonal high-resolution threshold photoelectron velocity map imaging spectrometer （VMI）. Intense and cold cluster anions were prepared in photoelectron- attachment processes upon pulsed UV laser ablation of metal target. Combining this anion source with TOFMS-VMI, the achieved mass resolution is about 200, and the electron ki- netic energy resolution is better than 3%, i.e., 30 meV for 1 eV electrons. More importantly, low-energy photoelectron imaging spectra for CH3S- and S2- at 611.46 nm are obtained. In both cases, the refined electron affinities are determined to be 1.86264-0.0020 eV for CH3S and 1.67444-0.0035 eV for S2, respectively. Preliminary results suggest that the apparatus is a powerful tool for estimating precise electron affinities values from threshold photoelectron imaging spectroscopy.
基金This work was supported by the National Natural Science Foundation of China （No.10704083）,the Innovation Foundation of Chinese Academyof Sciences （No.KJCX1-YW-N30）, and the Public Science and Technology Program of Shenzhen （No.SY200806260026A）.
文摘The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.21073188）.
文摘The wavelength dependence of photoelectron angular distributions （PADs） of two-photon detachment of Cu^- has been directly studied by using the photoelectron map imaging. Results show that for the laser field intensity of 6.0×10^10W/cm^2, PADs exhibit dramatic change with the external field wavelength. Comparison between the experimental observation and the lowest-order perturbation theory prediction indicates that the pattern of PADs can be explained by the interference of the s and d partial waves in the final state. Relative contri- butions of s and d partial waves in the two-photon detachment at different laser wavelengths are obtained.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10774513,61078080,11174304,and 11104167)the National Basic Research Program of China (Grant Nos. 2010CB923203 and 2011CB808103)
文摘By developing a full quantum scattering theory of high-order above-threshold ionization,we study the energy spectra and the angular distributions of photoelectrons from atoms with intense laser fields shining on them.We find that real rescattering can occur many times,and even infinite times.The photoelectrons from the rescattering process form a broad plateau in the kinetic-energy spectrum.We further disclose a multiple-plateau structure formed by the high-energy photoelectrons,which absorb many photons during the rescattering process.Moreover,we find that both the angular distributions and the kinetic-energy spectra of photoelectrons obey the same scaling law as that for directly emitted photoelectrons.
文摘We investigated the structural evolution and elecfronic properties of ConC3-/0 and ConC4-/0 （n=1-4） clusters by using mass-selected photoelectron spectroscopy and density functional theory calculations. The adiabatic and vertical detachment energies of CO1-4C3- and COl-4C4- were obtained from their photoelectron spectra. By comparing the theoretical results with the experimental data, the global minimum structures were determined. The results indicate that the carbon atoms of ConC3-/0 and ConC4-/0 （n=1-4） are separated from each other gradually with increasing number of cobalt atoms but a C2 unit still remains at n=4. It is interesting that the Co2C3- and Co2C4- anions have planar structures whereas the neutral Co2C3 and Co2C4 have linear structures with the Co atoms at two ends. The Co3C3- anion has a planar structure with a Co2C2 four-membered ring and a Co3C four-membered ring sharing a Co-Co bond, while the neutral Co3C3 is a three-dimensional structure with a C2 unit and a C atom connecting to two faces of the Co3 triangle.
基金This work was supported by the National Natural Science Foundation of China （No.20933003 and No.21073186） and the National Basic Research Program of China （No.2007CBSI5203, No.2010CB732306, and No.2007CBSI5201）.
文摘The AgOCH3- and Ag-（CH3OH）x（x=l, 2） anions are studied by photoelectron imaging as well as ab initio calculations. The adiabatic and vertical detachment energies （ADE and VDE） of AgOCH3- are determined as 1.29（2） and 1.34（2） eV, respectively, from the vibrational resolved photoelectron spectrum. The Ag-（CH3OH）l,2 anionic complexes are characterized as metal atomic anion solvated by the CH3OH molecules with the electron mainly localized on the metal. The photoelectron spectra of Ag-（CH3OH）x （x=O, 1, 2） show a gradual increase in VDE with increasing x, due to the solvent stabilization. Evidence for the methanol-methanol hydrogen bonding interactions appears when the Ag- is solvated by two methanol molecules.
基金Wei-jun Zheng acknowledges the Knowledge Innovation Program of the Chinese Academy of Sciences （No.KJCX2-EW-H01） and Hong-guang Xu acknowl- edges the National Natural Science Foundation of China （No.21103202） for financial support. The theoretical calculations were conducted on the ScGrid and Deep- Comp 7000 of the Supercomputing Center, Computer Network Information Center of the Chinese Academy of Sciences.
文摘The growth pattern and electronic properties of TiGen^- （n=7-12） clusters were investigated using anion photoelectron spectroscopy and density functional theory calculations. For both anionic and neutral TiGen clusters, a half-encapsulated boat-shaped structure appears at n=8, and the boat-shaped structure is gradually covered by the additional Ge atoms to form Gen cage at n=9-11. TiGe12^- cluster has a distorted hexagonal prism cage structure. According to the natural population analysis, the electron transfers from the Gen framework to the Ti atom for TiGen^-/0 clusters at n=8-12, implying that the electron transfer pattern is related to the structural evolution.
文摘Methanol/TiO2（110） is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO2, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO2（110） surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO2 substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytie process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.
基金supported by the National Natural Science Foundation of China (Grant Nos.91021009 and 10874102)the Research Fund for the Doctoral Program of Higher Education,China (Grant No.200804220004)
文摘We investigate Autler-Townes splitting in the photoelectron spectra of K2 molecule driven by pump-probe pulses via employing the time-dependent wave packet approach. It is found that the magnitude of Aulter-Townes splitting varies with the wavelength of the intense laser pulse. In particular, the phenomenon of Aulter-Townes splitting vanishes for the far-off resonance of the pump pulse. Also, the split peaks of Autler Townes in the case of resonant pump pulse give us an approach to directly obtaining the transition dipole moment of a molecule.
基金This work was supported by the National Natural Science Foundation of China （No.21222308, No.21103187, and No.21133006）, the Chinese Academy of Sciences, and the National Basic Research Program of China （No. 2013CB922200）.
文摘We present photoelectron angular distribution of the aligned molecular ion H2^＋ by intense ultrashort attosecond extreme ultraviolet laser pulses from numerical solutions of timedependent Schrodinger equations. Photoionization from a superposition state of the ground 1sσg and the excited 2pσu states with pulses at photon energies above the ionization potential, hω〉Ip, and intensity 10^14 W/cm^2, yields pulse duration dependent asymmetry of photoelectron angular distributions. We attribute the asymmetry to the periodical oscillation of the coherent electron wave packets, resulting from the interference of the two electronic states. For the processes with long pulse durations, such duration dependence is absent and symmetric angular distributions are obtained.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11827806,11874368 and 61675213).
文摘We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_(1/2) and 5P_(3/2) in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.
基金supported by the B-type Strategic Priority Program No.XDB41000000funded by the Chinese Academy of Sciences and the pre-research project on Civil Aerospace Technologies No.D020105funded by China's National Space Administration(CNSA).The authors also acknowledge support from the National Natural Science Foundation of China(NSFC)through grants 41904154,41525015,and 41774186.
文摘An important population of the dayside Martian ionosphere are photoelectrons that are produced by solar Extreme Ultraviolet and X-ray ionization of atmospheric neutrals.A typical photoelectron energy spectrum is characterized by a distinctive peak near 27 eV related to the strong solar HeⅡ emission line at 30.4 nm,and an additional peak near 500 eV related to O Auger ionization.In this study,the extensive measurements made by the Solar Wind Electron Analyzer on board the recent Mars Atmosphere and Volatile Evolution spacecraft are analyzed and found to verify the scenario that Martian ionosphere photoelectrons are driven by solar radiation.We report that the photoelectron intensities at the centers of both peaks increase steadily with increasing solar ionizing flux below 90 nm and that the observed solar cycle variation is substantially more prominent near the O Auger peak than near the HeⅡ peak.The latter observation is clearly driven by a larger variability in solar irradiance at shorter wavelengths.When the solar ionizing flux increases from 1 mW·m^-2 to 2.5 mW·m^-2,the photoelectron intensity increases by a factor of 3.2 at the HeⅡ peak and by a much larger factor of 10.5 at the O Auger peak,both within the optically thin regions of the Martian atmosphere.
