Dong-Dong Ni

OSCILLATOR STRENGTHS OF VIBRIONIC EXCITATIONS OF NITROGEN DETERMINED BY THE DIPOLE (γ,γ) METHOD

The oscillator strengths of the valence-shell excitations of molecular nitrogen have significant applicational values in studies of the Earths atmosphere and interstellar gases. In this work, the absolute oscillator strengths of the valence-shell excitations of molecular nitrogen in 12.3?13.4 eV were measured by the novel dipole (?, ?) method, in which the high-resolution inelastic X-ray scattering is operated at a negligibly small momentum transfer and can simulate the photoabsorption process. Because the experimental technique used in the present work is distinctly different from those used previously, the present experimental results give an independent cross-check to previous experimental and theoretical data. The excellent coincidence of the present results with the dipole (e, e) and those that were extrapolated indicates that the present oscillator strengths can serve as benchmark data.

The realization of the dipole (γ, γ) method and its application to determine the absolute optical oscillator strengths of helium.

The dipole (γ, γ) method, which is the inelastic x-ray scattering operated at a negligibly small momentum transfer, is proposed and realized to determine the absolute optical oscillator strengths of the vanlence-shell excitations of atoms and molecules. Compared with the conventionally used photoabsorption method, this new method is free from the line saturation effect, which can seriously limit the accuracies of the measured photoabsorption cross sections for discrete transitions with narrow natural linewidths. Furthermore, the Bethe-Born conversion factor of the dipole (γ, γ) method varies much more slowly with the excitation energy than does that of the dipole (e, e) method. Absolute optical oscillator strengths for the excitations of 1s2 → 1 snp(n = 3 − 7) of atomic helium have been determined using the high-resolution dipole (γ, γ) method, and the excellent agreement of the present measurements with both those measured by the dipole (e, e) method and the previous theoretical calculations indicates that the dipole (γ, γ) method is a powerful tool to measure the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules.

The absolute optical oscillator strengths of the 3p54 s and excitations of argon measured by the dipole (γ, γ) method

The optical oscillator strengths of the 3p54s and excitations of argon are of crucial importance in determining the elemental abundance of argon from astronomical observations. Substantial efforts have been made to determine the optical oscillator strengths of the 3p54s and transitions of argon, however, significant discrepancies among the reported values still exist. In this work, the absolute optical oscillator strengths of the 3p54s and transitions of argon have been measured by a newly developed high-resolution dipole (γ, γ) method. A comprehensive comparison with the previous experimental and theoretical data was then made as a cross-check.

Integral cross sections of the dipole‐allowed excitations of nitrogen molecule studied by the fast electron scattering

The integral cross sections (ICSs) of the electron scattering of nitrogen molecule are of great importance to the understanding of many different aspects of atmospheric physics. In the present work, the generalized oscillator strengths (GOSs) of the valence-shell excitations of b1Πu, b′1Σu+, c31Πu, c4′1Σu+, and o31Πu of nitrogen have been determined by fast-electron scattering at an incident electron energy of 1500 eV and an energy resolution of 70 meV. By crosschecking strictly the present results with the previous electron scattering and inelastic x-ray scattering (IXS) ones, the accuracy and reliability of the GOSs for the corresponding dipole-allowed transitions of nitrogen are tested stringently. Based on the accurate GOSs of these dipole-allowed transitions, their ICSs are obtained systematically from the threshold to 5000 eV for the first time with the aid of the BE-scaling method, and the corresponding ICSs at the moderate and high energies are the only available data to the best of our knowledge.

Investigation of Compton profiles of molecular methane and ethane

The Compton profiles of methane and ethane molecules have been determined at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved near pz = 0. The density functional theory with aug-cc-pVTZ basis set was used to calculate the Compton profiles of methane and ethane. The present experimental Compton profiles are in better agreement with the theoretical calculations in the whole pz region than the previous experimental results, which indicates that the present experimental Compton profiles are accurate enough to serve as the benchmark data for methane and ethane molecules.

A 1-m non-resonant inelastic x-ray scattering spectrometer at BL15U, Shanghai Synchrotron Radiation Facility

We report the design, construction, and commissioning of a spectrometer for non-resonant inelastic x-ray scattering study installed at BL15U, Shanghai Synchrotron Radiation Facility. It features a 1-m vertical scattering arm. An energy resolution of 1.3 eV is achieved based on the 1 m Rowland circle and the diced Si(555) crystal analyzer with a fixed Bragg angle of about 88.8°. The inelastic squared form factors of 21S + 21P of helium with respect to the momentum transfer were measured and compared with the accurate and reliable theoretical calculations in order to verify the spectrometer. Furthermore, the spectrometer is designed to work in the momentum transfer region of 0 Å-1 < q < 8.68 Å-1 and to initially focus on the non-resonant inelastic x-ray scattering studies on gaseous samples.

Integral cross sections of the dipole-allowed excitations of nitrogen studied by fast electron scattering and X-ray scattering

The integral cross sections (ICSs) of the electron scattering of nitrogen molecule are of great importance to the understanding of many different aspects of atmospheric physics. Based on the generalized oscillator strengths (GOSs) of these dipole-allowed transitions crosschecked by the high-energy electron scattering and high-resolution X-ray scattering, their ICSs are obtained systematically from the threshold to 5000 eV for the first time with the aid of the BE-scaling method, and the corresponding ICSs at the moderate and high energies are the only available data to the best of our knowledge.

Investigation of Compton Profile of Molecular Propane

The experimental Compton profile of the propane molecule is measured at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved near pz = 0. The calculated Compton profile by the density functional theory with aug-cc-pVTZ basis set reproduces the experimental observation very well. The joint experimental and theoretical investigation provides the benchmark data of the electronic structure of propane.

Fast-electron-impact study on excitations of 4d electron of xenon

The electron energy loss spectrum of the 4d excitations of xenon was measured at an incident electron energy of 1500 eV and a scattering angle of 6°. Besides the optically allowed transitions of and the optically forbidden transitions of and were observed. The measured features are assigned with the help of the calculation by the Cowan Code. The line profile parameters of both optically allowed transitions and optically forbidden ones were determined and compared with the previous available data. It is found that the natural widths of both dipole-allowed and dipole-forbidden excitations are approximately identical, which means the spectator transitions dominate the resonant Auger effect for both dipole-allowed and dipole-forbidden transitions.

Compton profile of molecular hydrogen

The Compton profile of molecular hydrogen has been determined at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved at pz = 0. Different theoretical methods, i.e., the density functional method, and the Hartree?Fock method, were used to calculate the Compton profiles of hydrogen with different basis sets, and the theoretical calculations are in agreement with the experimental observation in the whole pz region. Compared with the HF calculation, the DFT-B3LYP ones are in better agreement with the present experiment, which indicates the electron correlation effect is very important to describe the wavefunction in the ground state of hydrogen.