In this study,we report the design and simulation of an electrostatic ion lens system consisting of 22 round metal plates.The opening of the extractor plate is covered withmetal mesh,which is for shielding the interac...In this study,we report the design and simulation of an electrostatic ion lens system consisting of 22 round metal plates.The opening of the extractor plate is covered withmetal mesh,which is for shielding the interaction region of the lens system from the high DC voltages applied to all other plates than the repeller and extractor plates.The Simion simulation shows that both velocity-mapping and time focusing can be achieved simultaneously when appropriate voltages are applied to each of the plates.This makes the ion lens system be able to focus large ionic volumes in all three dimensions,which is an essential requirement for crossed ion-molecule scattering studies.A three-dimensional ion velocity measurement system with multi-hit and potential multi-mass capability is built,which consists of a microchannel plate(MCP),a P47 phosphor screen,a CMOS camera,a fast photomultiplier tube(PMT),and a high-speed digitizer.The two velocity components perpendicular to the flight axis are measured by the CMOS camera,and the time-of-flight,from which the velocity component along the flight axis can be deduced,is measured by the PMT.A Labview program is written to combine the two measurements for building the full three-dimensional ion velocity in real time on a frame-by-frame basis.The multi-hit capability comes from the fact that multiple ions from the camera and PMT in the same frame can be correlated with each other based on their various intensities.We demonstrate this by using the photodissociation of CH31 at 304 nm.展开更多
A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectrosco...A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy combined with theoretical calculations.CO ligand-mediated reactivity in CO oxidation of yttrium-nickel monoxide carbonyl complexes was experimentally and theoretically identified.During the consecutive CO adsorption,aμ^(2)-O linear structure was most favorable for YNiO(CO)_(n)^(-)(n=1,2),then a structure in which the terminal O was bonded to the Y atom became favored for YNiO(CO)_(3)^(-),and finally a structure bearing a CO_(2)moiety was most favorable for YNiO(CO)_(n)^(-)(n=4,5).Theoretical calculations indicated that the Ni atom acted as an electron acceptor and accumulated electron density at n≤3,and then served as an electron donor along with the Y atom to contribute electron density in the rearrangement that accompanied CO oxidation at n>3.展开更多
We have obtained the high-resolution threshold photoelectron （TPE） spectra of chlorobenzene C6HaCl （X1A1）, propargyl radical C3H3 （X2B1）, and allyl radical C3H5 （X2A1） by employing the vacuum ultraviolet （VUV...We have obtained the high-resolution threshold photoelectron （TPE） spectra of chlorobenzene C6HaCl （X1A1）, propargyl radical C3H3 （X2B1）, and allyl radical C3H5 （X2A1） by employing the vacuum ultraviolet （VUV） laser velocity-map-imaging-TPE （VUV-VMI-TPE） method. The photoelectron energy resolution of 1-2 cm^-1 observed for the VUV-VMI-TPE method is comparable to that achieved in VUV laser pulsed-field ionization-photoelectron （VUV-PFI-PE） measurements. Similar to VUV-PFI-PE measurements, the energy resolutions for VUV-VMI-photoelectron （VUV-VMI-PE） and VUV-VMI-TPE measurements are found to depend on the dc electric field F in V/cm used at the photoionization region for electron extraction. The decrease of the ionization thresholds of C6H5Cl and C3H3 observed as a function of F shows that the Stark shift correction for VUV-VMI-TPE measurements is governed by the formula -3.1√F in cm^-1, which is half of the classical prediction of -6.1v/F in cm^-1. We have also measured the VUV-VMI-PE spectra of C6H5Cl and C3H5 at VUV energies near their ionization thresholds. The cationic vibrational bands observed in the VUV-VMI-PE measurements were assigned to be the vibrational progression, nv7＋ （n=0-3）, for C3H＋. The higher experimental sensitivity and similar energy resolutions achieved in VUV-VMI-TPE compared to VUV-PFI-PE measurements make the VUV-VMI- TPE method an excellent alternative for high-resolution VUV-PFI-PE measurements.展开更多
Owing to its convenience and accuracy in providing detailed information about quantum state populations and angular distributions of reaction products,the velocity map imaging technique has been extensively employed i...Owing to its convenience and accuracy in providing detailed information about quantum state populations and angular distributions of reaction products,the velocity map imaging technique has been extensively employed in crossed beam experiments for product detection.In crossed beam experiments,the two reactant beams always exhibit certain spreads in both magnitude and direction of the velocity,which will blur the scattered product images and lower the resolution of product detection.To systematically investigate the influence of reactant velocity spreads on the resolution of product detection in crossed beam experiments,a general model based on velocity vector analysis is constructed and presented here.The impacts of spreads of the magnitude and direction of the reactant velocities on the image resolution under three typical experimental conditions are analyzed,and ways for improving the resolution are briefly discussed.Guided by the above analysis,a fine adjustment of the Ar^(+)ion beam was performed,and the product image resolution for the charge transfer reaction Ar^(+)(^(2)P_(3/2))+N_(2)is effectively improved,particularly in the backward scattering region,which provides more accurate information on the reaction dynamics.展开更多
The autoionization branching ratios from Eu 4f76p1/26 d [J] autoionizing states to its 4f76s+(9So), 4f76s+(7So), and4f75d+(9Do) final ionic states are investigated with the combination of the three-step laser excitati...The autoionization branching ratios from Eu 4f76p1/26 d [J] autoionizing states to its 4f76s+(9So), 4f76s+(7So), and4f75d+(9Do) final ionic states are investigated with the combination of the three-step laser excitation and the velocity-map imaging technique. These different autoionizing states are excited via 4f76s6d8 DJ [J = 5/2, 7/2, and 9/2] intermediate states, respectively. The experimental photoelectron images are obtained, from which energy distributions of ejected electrons are achieved with the mathematical transformation. Furthermore, the energy dependence of the branching ratio is investigated within the autoionization resonance, by which population inversion is observed as an important characteristic.The J-dependence is also studied systematically. The validity of the well-known isolated core excitation technique used for obtaining the autoionization spectrum is also studied.展开更多
The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f^76p_（1/2）nd auto-ionizing states are investigated with the velocity-map-imaging technique.To populate the above auto-ion...The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f^76p_（1/2）nd auto-ionizing states are investigated with the velocity-map-imaging technique.To populate the above auto-ionizing states,the relevant bound Rydberg states have to be detected first.Two new bound Rydberg states are identified in the region between41150 cm^（-1）and 44580 cm^（-1）,from which auto-ionization spectra of the Eu 4f^76p_（1/2）nd states are observed with isolated core excitation method.With all preparations above,the branching ratios from the above auto-ionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically.Energy dependence of branching ratios and anisotropy parameters within the auto-ionization spectra are carefully analyzed,followed by a qualitative interpretation.展开更多
Metal carbides play an important role in catalysis and functional materials.However,the structural characterization of metal carbide clusters has been proven to be a challenging experimental target due to the difficul...Metal carbides play an important role in catalysis and functional materials.However,the structural characterization of metal carbide clusters has been proven to be a challenging experimental target due to the difficulty in size selection.Here we use the size-specific photoelectron velocity-map imaging spectroscopy to study the structures and properties of platinum carbide clusters.Quantum chemical calculations are carried out to identify the structures and to assign the experimental spectra.The results indicate that the cluster size of the chain-to-ring structural evolution for the PtC_(n)^(-)anions occurs at n=14,whereas that for the PtC_(n) neutrals at n=10,revealing a significant effect of charge on the structures of metal carbides.The greatest importance of these building blocks is the strong preference of the Pt atom to expose in the outer side of the chain or ring,exhibiting the active sites for catalyzing potential reactions.These findings provide unique spectroscopic snapshots for the formation and growth of platinum carbide clusters and have important implications in the development of related single-atom catalysts with isolated metal atoms dispersed on supports.展开更多
The photodissociation dynamics of Br-C bond cleavage for BrCN in the wavelength region from 225 nm to 260 nm has been studied by our homebuilt time-slice velocity-map imaging setup.The images for both of the ground st...The photodissociation dynamics of Br-C bond cleavage for BrCN in the wavelength region from 225 nm to 260 nm has been studied by our homebuilt time-slice velocity-map imaging setup.The images for both of the ground state Br(^(2)P_(3/2))and spin-orbit excited Br^(*)(^(2)P_(1/2))channels are obtained at several photodissociation wavelengths.From the analysis of the translational energy release spectra,the detailed vibrational and rotational distributions of CN products have been measured for both of the Br and Br^(*)channels.It is found that the internal excitation of the CN products for the Br^(*)channel is colder than that for the Br channel.The most populated vibrational levels of the CN products are v=0 and 1 for the Br and Br^(*)channels,respectively.For the Br channel,the photodissociation dynamics at longer wavelengths are found to be different from those at shorter wavelengths,as revealed by their dramatically different vibrational and rotational excitations of the CN products.展开更多
Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes suc...Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes such as Fischer-Tropsch chemistry and alcohol synthesis.Here,we use mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to study the reactions of CO molecules with several heterobinuclear transition metal-iron clusters M-Fe(M=Ti,V,Cr).The mass spectra reveal the favorable formation of MFe(CO)_(4)^(-)with relatively high thermodynamic stability.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) complexes are established to have a metal-Fe bonded M-Fe(CO)_(4) structure with C_(3 v) geometry.While the positive charge and unpaired electrons are mainly located on the M atom,the natural charge of Fe(CO)_(4) is about-2 e.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) can be seen as being formed via the interactions between the M^(+)fragment and the [Fe(CO)_(4)]^(2-)core,which satisfies the 18-electron rule.The CO molecules are remarkably activated in these MFe(CO)_(4)^(-).These results shed insight into the structure-reactivity relationship of heterobinuclear transition metal carbonyls and would have important implications for understanding of CO activation on alloy surfaces.展开更多
The geometric structures and vibration frequencies of para-chlorofluorobenzene(p-Cl FPh)in the first excited state of neutral and ground state of cation were investigated by resonanceenhanced multiphoton ionization an...The geometric structures and vibration frequencies of para-chlorofluorobenzene(p-Cl FPh)in the first excited state of neutral and ground state of cation were investigated by resonanceenhanced multiphoton ionization and slow electron velocity-map imaging.The infrared spectrum of S0 state and absorption spectrum for S1←S0 transition in p-Cl FPh were also recorded.Based on the one-color resonant two-photon ionization spectrum and two-color resonant two-photon ionization spectrum,we obtained the adiabatic excited-state energy of p-Cl FPh as 36302±4 cm^-1.In the two-color resonant two-photon ionization slow electron velocity-map imagin spectra,the accurate adiabatic ionization potential of p-Cl FPh was extrapolated as 72937±8 cm^-1 via threshold ionization measurement.In addition,FranckCondon simulation was performed to help us confidently ascertain the main vibrational modes in the S1 and D0 states.Furthermore,the mixing of vibrational modes between S0→S1 and S1→D0 has been analyzed.展开更多
Electron affinities(EA)of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures.In the present work,we report the high-resolution phot...Electron affinities(EA)of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures.In the present work,we report the high-resolution photoelectron spectra of atomic cerium anion Ce−using the slow electron velocity-map imaging method in combination with a cold ion trap.The electron affinity of Ce is determined to be 4840.62(21)cm^-1 or 0.600160(26)eV.Moreover,several excited states of Ce(^4H9/2,^4I9/2,^2H9/2,^2G9/2,^2G7/2,^4H13/2,^2F5/2,and ^4I13/2)are observed.展开更多
The present review focused on selected, recent experimental progress of photodissociation dynamics of small molecules covering the vacuum ultraviolet (VUV) range from 6 eV to 20 eV. These advancements come about due t...The present review focused on selected, recent experimental progress of photodissociation dynamics of small molecules covering the vacuum ultraviolet (VUV) range from 6 eV to 20 eV. These advancements come about due to the available laser based VUV light sources along with the developments of advanced experimental techniques, including the velocitymap imaging (VMI), H-atom Rydberg tagging time-of-flight (HRTOF) techniques, as well as the two-color tunable VUV-VUV laser pump-probe detection method. The applications of these experimental techniques have allowed VUV photodissociation studies of many diatomic and triatomic molecules to quantum state-to-state in detail. To highlight the recent accomplishments, we have summarized the results on several important molecular species, including H2 (D2, HD), CO, N2, NO, O2, H2O (D2O, HOD), CO2, and N2O. The detailed VUV photodissociation studies of these molecules are of astrochemical and atmospheric relevance. Since molecular photodissociation initiated by VUV excitation is complex and is often governed by multiple electronic potential energy surfaces, the unraveling of the complex dissociation dynamics requires state-to-state cross section measurements. The newly constructed Dalian Coherent Light Source (DCLS), which is capable of generating coherent VUV radiation with unprecedented brightness in the range of 50-150 nm, promises to propel the photodissociation experiment to the next level.展开更多
With recent developments of sophisticated experimental techniques and advanced theoretical methods/computations, the field of chemical dynamics has reached the point that theoryexperiment comparisons can be made at a ...With recent developments of sophisticated experimental techniques and advanced theoretical methods/computations, the field of chemical dynamics has reached the point that theoryexperiment comparisons can be made at a quantitative level in very fine details for a prototypical A+BC system. As the system becomes larger, more degrees of freedom are involved and the complexity increases exponentially. At the same time, the multifaceted nature of polyatomic systems also opens up the possibilities for observing many new chemistry and novel phenomena|a land of opportunities. For the past 15 years or so my laboratory has delved into the reaction dynamics of methane+X (X: F, Cl, O(3P), and OH). This effort shifts the paradigm in the field of reaction dynamics by making the title reaction a benchmark polyatomic system. In this account, I shall disclose my thinking behind some of the key concepts and methods we introduced and how the unexpectedly discovered phenomena led to other uncharted territories. Those ndings not only enrich our understanding of the specific reactions we studied at the most fundamental level and inspire the theoretical developments, but also shape our thinking and lay the foundation for future explorations of different aspects of the multifaceted nature of polyatomic reactivity.展开更多
Accurate determinations of bond dissociation energies(BDEs)and the corresponding enthalpies of formation derived from them are of fundamental importance,while on the other hand also very challenging in chemistry.In th...Accurate determinations of bond dissociation energies(BDEs)and the corresponding enthalpies of formation derived from them are of fundamental importance,while on the other hand also very challenging in chemistry.In this study,we demonstrate a direct experimental scheme for measuring the BDEs of^(14)N_(2),^(14N)^(15)N and^(15)N_(2)to an accuracy of a few wavenumbers.The high-resolution quantum-state-selected velocity-mapped ion images for several rotational levels with accurately known spectroscopic term energies slightly above the dissociation limit N(^(2)D_(5/2,3/2))+N(^(2)D_(5/2,3/2))were obtained for each of the dinitrogen isotopologue molecules.A linear fit between squares of the radii of the quantum-state-selected images and the spectroscopic term energies gives out an accurate measurement of the threshold D0 for dissociating into the channel N(^(2)D_(5/2,3/2))+N(^(2)D_(5/2,3/2)).The BDEs of^(4)N_(2),^(14N)^(15)N and^(15)N_(2)into the lowest channel N(4S)+N(4S)are independently determined to be 78,688±3,78,705±4 and 78,728±4 cm^(−1),respectively.These independently determined BDEs are found to give a consistent value of De after considering the zero-point energies for each of the isotopologues,implying the reliability of the present measurement.Comparisons with several previous measurements and theoretical calculations are discussed.The experimental scheme demonstrated in this study should be generally applicable for precisely determining the BDEs of many other diatomic molecules.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
基金This work is supported by the Program for Young Outstanding Scientists of Institute of Chemistry,Chinese Academy of Science,and Beijing National Laboratory for Molecular SciencesHong Gao and Li-chang Guan are also supported by the K.C.Wong Education Foundation.
文摘In this study,we report the design and simulation of an electrostatic ion lens system consisting of 22 round metal plates.The opening of the extractor plate is covered withmetal mesh,which is for shielding the interaction region of the lens system from the high DC voltages applied to all other plates than the repeller and extractor plates.The Simion simulation shows that both velocity-mapping and time focusing can be achieved simultaneously when appropriate voltages are applied to each of the plates.This makes the ion lens system be able to focus large ionic volumes in all three dimensions,which is an essential requirement for crossed ion-molecule scattering studies.A three-dimensional ion velocity measurement system with multi-hit and potential multi-mass capability is built,which consists of a microchannel plate(MCP),a P47 phosphor screen,a CMOS camera,a fast photomultiplier tube(PMT),and a high-speed digitizer.The two velocity components perpendicular to the flight axis are measured by the CMOS camera,and the time-of-flight,from which the velocity component along the flight axis can be deduced,is measured by the PMT.A Labview program is written to combine the two measurements for building the full three-dimensional ion velocity in real time on a frame-by-frame basis.The multi-hit capability comes from the fact that multiple ions from the camera and PMT in the same frame can be correlated with each other based on their various intensities.We demonstrate this by using the photodissociation of CH31 at 304 nm.
基金supported by the Natural Science Foundation of Shandong Province(No.ZR2021QB215)the National Natural Science Foundation of China(Nos.22273101,22125303,92061203,21327901,and 22288201)+2 种基金Dalian Institute of Chemical Physics(No.DICP I202437)the Talent Induction Program for Youth Innovation Teams in Colleges and Universities of Shandong Province(No.2022-2024)the Talent Introduction Research Start-up Funds of Ludong University(No.20212026)。
文摘A series of heteronuclear yttrium-nickel monoxide carbonyl complexes YNiO(CO)_(n)^(-)(n=1-5)were generated in a pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy combined with theoretical calculations.CO ligand-mediated reactivity in CO oxidation of yttrium-nickel monoxide carbonyl complexes was experimentally and theoretically identified.During the consecutive CO adsorption,aμ^(2)-O linear structure was most favorable for YNiO(CO)_(n)^(-)(n=1,2),then a structure in which the terminal O was bonded to the Y atom became favored for YNiO(CO)_(3)^(-),and finally a structure bearing a CO_(2)moiety was most favorable for YNiO(CO)_(n)^(-)(n=4,5).Theoretical calculations indicated that the Ni atom acted as an electron acceptor and accumulated electron density at n≤3,and then served as an electron donor along with the Y atom to contribute electron density in the rearrangement that accompanied CO oxidation at n>3.
基金This work was supported by the National Science Foundation under CHE-0910488 and CHE-1462172. C. Y. Ng also acknowledges the support by the Chemi- cal Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, （US） Department of Energy （DOE） under Contract No.DEFG02-02ER15306.
文摘We have obtained the high-resolution threshold photoelectron （TPE） spectra of chlorobenzene C6HaCl （X1A1）, propargyl radical C3H3 （X2B1）, and allyl radical C3H5 （X2A1） by employing the vacuum ultraviolet （VUV） laser velocity-map-imaging-TPE （VUV-VMI-TPE） method. The photoelectron energy resolution of 1-2 cm^-1 observed for the VUV-VMI-TPE method is comparable to that achieved in VUV laser pulsed-field ionization-photoelectron （VUV-PFI-PE） measurements. Similar to VUV-PFI-PE measurements, the energy resolutions for VUV-VMI-photoelectron （VUV-VMI-PE） and VUV-VMI-TPE measurements are found to depend on the dc electric field F in V/cm used at the photoionization region for electron extraction. The decrease of the ionization thresholds of C6H5Cl and C3H3 observed as a function of F shows that the Stark shift correction for VUV-VMI-TPE measurements is governed by the formula -3.1√F in cm^-1, which is half of the classical prediction of -6.1v/F in cm^-1. We have also measured the VUV-VMI-PE spectra of C6H5Cl and C3H5 at VUV energies near their ionization thresholds. The cationic vibrational bands observed in the VUV-VMI-PE measurements were assigned to be the vibrational progression, nv7＋ （n=0-3）, for C3H＋. The higher experimental sensitivity and similar energy resolutions achieved in VUV-VMI-TPE compared to VUV-PFI-PE measurements make the VUV-VMI- TPE method an excellent alternative for high-resolution VUV-PFI-PE measurements.
基金supported by the National Natural Science Foundation of China(No.22373107)Beijing National Laboratory for Molecular Sciences(BNLMSCXXM-202406)Hong Gao is also supported by the Innovation Capability Support Program of Shaanxi Province(2023-CX-TD-49).
文摘Owing to its convenience and accuracy in providing detailed information about quantum state populations and angular distributions of reaction products,the velocity map imaging technique has been extensively employed in crossed beam experiments for product detection.In crossed beam experiments,the two reactant beams always exhibit certain spreads in both magnitude and direction of the velocity,which will blur the scattered product images and lower the resolution of product detection.To systematically investigate the influence of reactant velocity spreads on the resolution of product detection in crossed beam experiments,a general model based on velocity vector analysis is constructed and presented here.The impacts of spreads of the magnitude and direction of the reactant velocities on the image resolution under three typical experimental conditions are analyzed,and ways for improving the resolution are briefly discussed.Guided by the above analysis,a fine adjustment of the Ar^(+)ion beam was performed,and the product image resolution for the charge transfer reaction Ar^(+)(^(2)P_(3/2))+N_(2)is effectively improved,particularly in the backward scattering region,which provides more accurate information on the reaction dynamics.
基金supported by the National Natural Science Foundation of China(Grant No.11174218)
文摘The autoionization branching ratios from Eu 4f76p1/26 d [J] autoionizing states to its 4f76s+(9So), 4f76s+(7So), and4f75d+(9Do) final ionic states are investigated with the combination of the three-step laser excitation and the velocity-map imaging technique. These different autoionizing states are excited via 4f76s6d8 DJ [J = 5/2, 7/2, and 9/2] intermediate states, respectively. The experimental photoelectron images are obtained, from which energy distributions of ejected electrons are achieved with the mathematical transformation. Furthermore, the energy dependence of the branching ratio is investigated within the autoionization resonance, by which population inversion is observed as an important characteristic.The J-dependence is also studied systematically. The validity of the well-known isolated core excitation technique used for obtaining the autoionization spectrum is also studied.
基金Project supported by the National Natural Science Foundation of China(Grant No.11174218)
文摘The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f^76p_（1/2）nd auto-ionizing states are investigated with the velocity-map-imaging technique.To populate the above auto-ionizing states,the relevant bound Rydberg states have to be detected first.Two new bound Rydberg states are identified in the region between41150 cm^（-1）and 44580 cm^（-1）,from which auto-ionization spectra of the Eu 4f^76p_（1/2）nd states are observed with isolated core excitation method.With all preparations above,the branching ratios from the above auto-ionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically.Energy dependence of branching ratios and anisotropy parameters within the auto-ionization spectra are carefully analyzed,followed by a qualitative interpretation.
基金supported by the National Natural Science Foundation of China(22273101,22103082,22125303,92061203,and 22288201)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(CAS)(2020187)+3 种基金the Innovation Program for Quantum Science and Technology(2021ZD0303304)Chinese Academy of Sciences(GJJSTD20220001)Dalian Institute of Chemical Physics(DICP DCLS201702)K.C.Wong Education Foundation(GJTD-201806)。
文摘Metal carbides play an important role in catalysis and functional materials.However,the structural characterization of metal carbide clusters has been proven to be a challenging experimental target due to the difficulty in size selection.Here we use the size-specific photoelectron velocity-map imaging spectroscopy to study the structures and properties of platinum carbide clusters.Quantum chemical calculations are carried out to identify the structures and to assign the experimental spectra.The results indicate that the cluster size of the chain-to-ring structural evolution for the PtC_(n)^(-)anions occurs at n=14,whereas that for the PtC_(n) neutrals at n=10,revealing a significant effect of charge on the structures of metal carbides.The greatest importance of these building blocks is the strong preference of the Pt atom to expose in the outer side of the chain or ring,exhibiting the active sites for catalyzing potential reactions.These findings provide unique spectroscopic snapshots for the formation and growth of platinum carbide clusters and have important implications in the development of related single-atom catalysts with isolated metal atoms dispersed on supports.
基金supported by the Beijing Municipal Natural Science Foundation(No.8212043)the support from Program for Young Outstanding Scientists of Institute of Chemistry,Chinese Academy of ScienceBeijing National Laboratory for Molecular Sciences。
文摘The photodissociation dynamics of Br-C bond cleavage for BrCN in the wavelength region from 225 nm to 260 nm has been studied by our homebuilt time-slice velocity-map imaging setup.The images for both of the ground state Br(^(2)P_(3/2))and spin-orbit excited Br^(*)(^(2)P_(1/2))channels are obtained at several photodissociation wavelengths.From the analysis of the translational energy release spectra,the detailed vibrational and rotational distributions of CN products have been measured for both of the Br and Br^(*)channels.It is found that the internal excitation of the CN products for the Br^(*)channel is colder than that for the Br channel.The most populated vibrational levels of the CN products are v=0 and 1 for the Br and Br^(*)channels,respectively.For the Br channel,the photodissociation dynamics at longer wavelengths are found to be different from those at shorter wavelengths,as revealed by their dramatically different vibrational and rotational excitations of the CN products.
基金supported by the National Natural Science Foundation of China (21688102, 21873097, and 92061203)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (CAS)(2020187)+3 种基金the Strategic Priority Research Program of CAS (XDB17000000)CAS (GJJSTD20190002)the International Partnership Program of CAS (121421KYSB20170012)the K.C.Wong Education Foundation (GJTD-2018-06)。
文摘Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes such as Fischer-Tropsch chemistry and alcohol synthesis.Here,we use mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to study the reactions of CO molecules with several heterobinuclear transition metal-iron clusters M-Fe(M=Ti,V,Cr).The mass spectra reveal the favorable formation of MFe(CO)_(4)^(-)with relatively high thermodynamic stability.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) complexes are established to have a metal-Fe bonded M-Fe(CO)_(4) structure with C_(3 v) geometry.While the positive charge and unpaired electrons are mainly located on the M atom,the natural charge of Fe(CO)_(4) is about-2 e.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) can be seen as being formed via the interactions between the M^(+)fragment and the [Fe(CO)_(4)]^(2-)core,which satisfies the 18-electron rule.The CO molecules are remarkably activated in these MFe(CO)_(4)^(-).These results shed insight into the structure-reactivity relationship of heterobinuclear transition metal carbonyls and would have important implications for understanding of CO activation on alloy surfaces.
基金the National Natural Science Foundation of China(No.11674003,No.21873003,No.21503003,No.11704004,and No.61475001)Anhui Natural Science Foundation(No.1908085QA17)+1 种基金support from Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)(No.U1501501)Super Computation Center of Shenzhen。
文摘The geometric structures and vibration frequencies of para-chlorofluorobenzene(p-Cl FPh)in the first excited state of neutral and ground state of cation were investigated by resonanceenhanced multiphoton ionization and slow electron velocity-map imaging.The infrared spectrum of S0 state and absorption spectrum for S1←S0 transition in p-Cl FPh were also recorded.Based on the one-color resonant two-photon ionization spectrum and two-color resonant two-photon ionization spectrum,we obtained the adiabatic excited-state energy of p-Cl FPh as 36302±4 cm^-1.In the two-color resonant two-photon ionization slow electron velocity-map imagin spectra,the accurate adiabatic ionization potential of p-Cl FPh was extrapolated as 72937±8 cm^-1 via threshold ionization measurement.In addition,FranckCondon simulation was performed to help us confidently ascertain the main vibrational modes in the S1 and D0 states.Furthermore,the mixing of vibrational modes between S0→S1 and S1→D0 has been analyzed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91736102 and 11974199)the National Key R&D Program of China(Grant No.2018YFA0306504).
文摘Electron affinities(EA)of most lanthanide elements still remain unknown owing to their relatively lower EA values and the fairly complicated electronic structures.In the present work,we report the high-resolution photoelectron spectra of atomic cerium anion Ce−using the slow electron velocity-map imaging method in combination with a cold ion trap.The electron affinity of Ce is determined to be 4840.62(21)cm^-1 or 0.600160(26)eV.Moreover,several excited states of Ce(^4H9/2,^4I9/2,^2H9/2,^2G9/2,^2G7/2,^4H13/2,^2F5/2,and ^4I13/2)are observed.
基金supported by the National Natural Science Foundation of China (No.21803072)the Program for Young Outstanding Scientists of Institute of Chemistry, Chinese Academy of Science (ICCAS)+2 种基金Beijing National Laboratory for Molecular Sciences (BNLMS)supported by the National Aeronautics and Space Administration Award #: 80NSSC18K0592National Science Foundation under CHE-1763319
文摘The present review focused on selected, recent experimental progress of photodissociation dynamics of small molecules covering the vacuum ultraviolet (VUV) range from 6 eV to 20 eV. These advancements come about due to the available laser based VUV light sources along with the developments of advanced experimental techniques, including the velocitymap imaging (VMI), H-atom Rydberg tagging time-of-flight (HRTOF) techniques, as well as the two-color tunable VUV-VUV laser pump-probe detection method. The applications of these experimental techniques have allowed VUV photodissociation studies of many diatomic and triatomic molecules to quantum state-to-state in detail. To highlight the recent accomplishments, we have summarized the results on several important molecular species, including H2 (D2, HD), CO, N2, NO, O2, H2O (D2O, HOD), CO2, and N2O. The detailed VUV photodissociation studies of these molecules are of astrochemical and atmospheric relevance. Since molecular photodissociation initiated by VUV excitation is complex and is often governed by multiple electronic potential energy surfaces, the unraveling of the complex dissociation dynamics requires state-to-state cross section measurements. The newly constructed Dalian Coherent Light Source (DCLS), which is capable of generating coherent VUV radiation with unprecedented brightness in the range of 50-150 nm, promises to propel the photodissociation experiment to the next level.
基金Academia Sinicathe Minster of Science and Technology of Taiwan (formerly, the National Science of Council) for their generous financial supports
文摘With recent developments of sophisticated experimental techniques and advanced theoretical methods/computations, the field of chemical dynamics has reached the point that theoryexperiment comparisons can be made at a quantitative level in very fine details for a prototypical A+BC system. As the system becomes larger, more degrees of freedom are involved and the complexity increases exponentially. At the same time, the multifaceted nature of polyatomic systems also opens up the possibilities for observing many new chemistry and novel phenomena|a land of opportunities. For the past 15 years or so my laboratory has delved into the reaction dynamics of methane+X (X: F, Cl, O(3P), and OH). This effort shifts the paradigm in the field of reaction dynamics by making the title reaction a benchmark polyatomic system. In this account, I shall disclose my thinking behind some of the key concepts and methods we introduced and how the unexpectedly discovered phenomena led to other uncharted territories. Those ndings not only enrich our understanding of the specific reactions we studied at the most fundamental level and inspire the theoretical developments, but also shape our thinking and lay the foundation for future explorations of different aspects of the multifaceted nature of polyatomic reactivity.
基金supported by the National Natural Science Foundation of China(21973100,22103090)the Program for Young Outstanding Scientists of Institute of Chemistry,Chinese Academy of Science(ICCAS)+2 种基金Beijing National Laboratory for Molecular Sciences(BNLMS)Hong Gao is also supported by the K.C.Wong Education FoundationPan Jiang is supported by the China Postdoctoral Science Foundation(2020TQ0324).
文摘Accurate determinations of bond dissociation energies(BDEs)and the corresponding enthalpies of formation derived from them are of fundamental importance,while on the other hand also very challenging in chemistry.In this study,we demonstrate a direct experimental scheme for measuring the BDEs of^(14)N_(2),^(14N)^(15)N and^(15)N_(2)to an accuracy of a few wavenumbers.The high-resolution quantum-state-selected velocity-mapped ion images for several rotational levels with accurately known spectroscopic term energies slightly above the dissociation limit N(^(2)D_(5/2,3/2))+N(^(2)D_(5/2,3/2))were obtained for each of the dinitrogen isotopologue molecules.A linear fit between squares of the radii of the quantum-state-selected images and the spectroscopic term energies gives out an accurate measurement of the threshold D0 for dissociating into the channel N(^(2)D_(5/2,3/2))+N(^(2)D_(5/2,3/2)).The BDEs of^(4)N_(2),^(14N)^(15)N and^(15)N_(2)into the lowest channel N(4S)+N(4S)are independently determined to be 78,688±3,78,705±4 and 78,728±4 cm^(−1),respectively.These independently determined BDEs are found to give a consistent value of De after considering the zero-point energies for each of the isotopologues,implying the reliability of the present measurement.Comparisons with several previous measurements and theoretical calculations are discussed.The experimental scheme demonstrated in this study should be generally applicable for precisely determining the BDEs of many other diatomic molecules.
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.
