Non-resonant inelastic X-ray scattering(NRIXS)is a new technique for atomic and molecular physics that allows one to measure the electronic structures and dynamic parameters of the ground and excited states of atoms a...Non-resonant inelastic X-ray scattering(NRIXS)is a new technique for atomic and molecular physics that allows one to measure the electronic structures and dynamic parameters of the ground and excited states of atoms and molecules in momentum space.There is a clearly understood physical picture of NRIXS,which reveals its remarkable advantages of satisfying the first Born approximation and being able to excite dipoleforbidden transitions.Various physical properties of atoms and molecules,such as their elastic and inelastic squared form factors,optical oscillator strengths,and Compton profiles,can be explored using NRIXS under different experimental conditions.In this paper,we review newly developed experimental methods for NRIXS,together with its characteristics and various applications,with emphasis on the new insights into excitation mechanism and other new information revealed by this technique.The intrinsic connections and differences between NRIXS and fast electron impact spectroscopy are elucidated.Future applications of this method to atomic and molecular physics are also described.展开更多
In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecule...In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecules have not been clearly elucidated.In this work,based on the molecular point group,the selection rules for the electric multipolarities of the electronic transitions of triatomic molecules are derived and summarized into several tables with the variation of molecular geometry in the transition process being considered.Based on the summarized selection rules,the electron energy loss spectra of H2O,CO_(2),and N_(2)O are identified,and the momentum transfer dependence behaviors of their valence-shell excitations are explained.展开更多
Recombination of Ar^(14+), Ar^(15+), Ca^(16+), and Ni^(19+) ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern...Recombination of Ar^(14+), Ar^(15+), Ca^(16+), and Ni^(19+) ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou,China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination(RR) and also dielectronic recombination(DR)processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semiclassical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code(FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV.However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q^(3.0), reproducing the low-energy recombination enhancement effects found in other previous experiments.展开更多
Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collis...Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several ke V. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths,and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.展开更多
The oscillator strengths of the valence-shell excitations of C_(2)H_(2) are extremely important for testing theoretical models and studying interstellar gases.In this study,the high-resolution inelastic x-ray scatteri...The oscillator strengths of the valence-shell excitations of C_(2)H_(2) are extremely important for testing theoretical models and studying interstellar gases.In this study,the high-resolution inelastic x-ray scattering(IXS)method is adopted to determine the generalized oscillator strengths(GOSs)of the valence-shell excitations of C_(2)H_(2) at a photon energy of10 ke V.The GOSs are extrapolated to their zero limit to obtain the corresponding optical oscillator strengths(OOSs).Through taking a completely different experimental method of the IXS,the present results offer the high energy limit for electron collision to satisfy the first Born approximation(FBA)and cross-check the previous experimental and theoretical results independently.The comparisons indicate that an electron collision energy of 1500 e V is not enough for C_(2)H_(2) to satisfy the FBA for the large squared momentum transfer,and the line saturation effect limits the accuracy of the OOSs measured by the photoabsorption method.展开更多
The accuracy of dielectronic recombination （DR） data for astrophysics related ions plays a key role in astrophysical plasma modeling. The absolute DR rate coefficient of Fe^17＋ ions was measured at the main cooler ...The accuracy of dielectronic recombination （DR） data for astrophysics related ions plays a key role in astrophysical plasma modeling. The absolute DR rate coefficient of Fe^17＋ ions was measured at the main cooler storage ring at the Institute of Modern Physics, Lanzhou, China. The experimental electron-ion collision energy range covers the first Rydberg series up to n = 24 for the DR resonances associated with the 2p1/2 →^2 p3/2△n= 0 core excitations. A theoretical calculation was performed by using FAC code and compared with the measured DR rate coefficient. Overall reasonable agreement was found between the experimental results and calculations. Moreover, the plasma rate coefficient was deduced from the experimental DR rate coefficient and compared with the available results from the literature. At the low energy range, significant discrepancies were found, and the measured resonances challenge state-of-the-art theory at low collision energies.展开更多
基金We acknowledge financial support from the National Natural Science Foundation of China(Grant Nos.U1932207 and U1732133)the National Key Research and Development Program of China(Grant Nos.2017YFA0303500 and 2017YFA0402300)+2 种基金The experiments reviewed here were supported by the beamtime approved by the Japan Synchrotron Radiation Research Institutethe National Synchrotron Radiation Research Center(NSRRC)the Shanghai Synchrotron Radiation Facility(SSRF).
文摘Non-resonant inelastic X-ray scattering(NRIXS)is a new technique for atomic and molecular physics that allows one to measure the electronic structures and dynamic parameters of the ground and excited states of atoms and molecules in momentum space.There is a clearly understood physical picture of NRIXS,which reveals its remarkable advantages of satisfying the first Born approximation and being able to excite dipoleforbidden transitions.Various physical properties of atoms and molecules,such as their elastic and inelastic squared form factors,optical oscillator strengths,and Compton profiles,can be explored using NRIXS under different experimental conditions.In this paper,we review newly developed experimental methods for NRIXS,together with its characteristics and various applications,with emphasis on the new insights into excitation mechanism and other new information revealed by this technique.The intrinsic connections and differences between NRIXS and fast electron impact spectroscopy are elucidated.Future applications of this method to atomic and molecular physics are also described.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0402300)the National Natural Science Foundation of China(Grant No.U1732133)the Science Fund from Chinese Academy of Sciences(Grant No.11320101003)
文摘In the electron or x-ray scattering experiment,the measured spectra at larger momentum transfer are dominated by the electric dipole-forbidden transitions,while the corresponding selection rules for triatomic molecules have not been clearly elucidated.In this work,based on the molecular point group,the selection rules for the electric multipolarities of the electronic transitions of triatomic molecules are derived and summarized into several tables with the variation of molecular geometry in the transition process being considered.Based on the summarized selection rules,the electron energy loss spectra of H2O,CO_(2),and N_(2)O are identified,and the momentum transfer dependence behaviors of their valence-shell excitations are explained.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0402300)the National Natural Science Foundation of China(Grant Nos.U1932207,11904371,and U1732133)。
文摘Recombination of Ar^(14+), Ar^(15+), Ca^(16+), and Ni^(19+) ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou,China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination(RR) and also dielectronic recombination(DR)processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semiclassical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code(FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV.However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q^(3.0), reproducing the low-energy recombination enhancement effects found in other previous experiments.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0402300)the National Natural Science Foundation of China(Grant Nos.U1932207 and 12104437)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB34000000)The financial support from the Heavy Ion Research Facility in Lanzhou(HIRFL)。
文摘Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several ke V. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths,and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Science(Grant No.XDB34000000)the National Natural Science Foundation of China(Grant Nos.U1932207 and 12104437)+3 种基金the National Key Research and Development Program of China(Grant No.2017YFA0402300)The support from the Heavy Ion Research Facility in Lanzhou(HIRFL)the BL12XU of SPring-8 with the approval of Japan Synchrotron Radiation Research Institute(Proposal No.2019A4275)“National”Synchrotron Radiation Research Center,Taiwan,China(Proposal No.2019-2-089-1)。
文摘The oscillator strengths of the valence-shell excitations of C_(2)H_(2) are extremely important for testing theoretical models and studying interstellar gases.In this study,the high-resolution inelastic x-ray scattering(IXS)method is adopted to determine the generalized oscillator strengths(GOSs)of the valence-shell excitations of C_(2)H_(2) at a photon energy of10 ke V.The GOSs are extrapolated to their zero limit to obtain the corresponding optical oscillator strengths(OOSs).Through taking a completely different experimental method of the IXS,the present results offer the high energy limit for electron collision to satisfy the first Born approximation(FBA)and cross-check the previous experimental and theoretical results independently.The comparisons indicate that an electron collision energy of 1500 e V is not enough for C_(2)H_(2) to satisfy the FBA for the large squared momentum transfer,and the line saturation effect limits the accuracy of the OOSs measured by the photoabsorption method.
基金Supported by the National Key R&D Program of China(2017YFA0402300)the National Natural Science Foundation of China through(11320101003,U1732133,11611530684)Key Research Program of Frontier Sciences,CAS(QYZDY-SSW-SLH006)
文摘The accuracy of dielectronic recombination （DR） data for astrophysics related ions plays a key role in astrophysical plasma modeling. The absolute DR rate coefficient of Fe^17＋ ions was measured at the main cooler storage ring at the Institute of Modern Physics, Lanzhou, China. The experimental electron-ion collision energy range covers the first Rydberg series up to n = 24 for the DR resonances associated with the 2p1/2 →^2 p3/2△n= 0 core excitations. A theoretical calculation was performed by using FAC code and compared with the measured DR rate coefficient. Overall reasonable agreement was found between the experimental results and calculations. Moreover, the plasma rate coefficient was deduced from the experimental DR rate coefficient and compared with the available results from the literature. At the low energy range, significant discrepancies were found, and the measured resonances challenge state-of-the-art theory at low collision energies.
