Ya-Wei Liu

Orientation of spin vectors of bright field disk galaxies in the local supercluster and its implication

Using the database of Photometric Atlas of Northern Bright Galaxies, the spatial orientation of 220 bright isolated held disk galaxies (41 SO, 174 S, and 5 Irr) in the Local Supercluster (LSC) has been analyzed. The sample of field galaxies is constructed by selecting disk galaxies with cz less than or equal to 3000 km s(-1) and excluding all galaxies of the groups or clusters of at least three members. Emphasis is placed on exploring morphological dependence of orientation of field galaxies.

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.

Oscillator strengths and integral cross sections for the valence-shell excitations of nitric oxide studied by fast electron impact.

The generalized oscillator strengths for the valence-shell excitations of A2Σ+, C2Π, and D2Σ+ electronic-states of nitric oxide have been determined at an incident electron energy of 1500 eV with an energy resolution of 70 meV. The optical oscillator strengths for these transitions have been obtained by extrapolating the generalized oscillator strengths to the limit that the squared momentum transfer approaches to zero, which give an independent cross-check to the previous experimental and theoretical results. The integral cross sections for the valence-shell excitations of nitric oxide have been determined systematically from the threshold to 2500 eV with the aid of the newly developed BE-scaling method for the first time. The present optical oscillator strengths and integral cross sections of the valence-shell excitations of nitric oxide play an important role in understanding many physics and chemistry of the Earths upper atmosphere such as the radiative cooling, ozone destruction, day glow, aurora, and so on.

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.

Investigations of the valence-shell excitations of molecular ethane by high-energy electron scattering

The differential cross sections and generalized oscillator strengths for the low-lying excitations of the valence-shell 1eg orbital electron in ethane have been measured for the first time at a high incident electron energy of 1500 eV and a scattering angular range of 1.5°-10°. A weak feature, termed X here, with a band center of about 7.5 eV has been observed, which was also announced by the previous experimental and theoretical studies. The dynamic behaviors of the generalized oscillator strengths for the 3s (8.7 eV), 3s+3p (9.31 eV, 9.41 eV), and X (∼7.5 eV) transitions on the momentum transfer squared have been obtained. The integral cross sections of these transitions from their thresholds to 5000 eV have been obtained with the aid of the BE-scaling (B is the binding energy and E is the excitation energy) method. The optical oscillator strengths of the above transitions determined by extrapolating their generalized oscillator strengths to the limit of the squared momentum transfer K2 → 0 are in good agreement with the ones from the photoabsorption spectrum [J. W. Au et al., Chem. Phys. 173, 209 (1993)], which indicates that the present differential cross sections, generalized oscillator strengths, and integral cross sections can serve as benchmark data.

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.

Inelastic squared form factors of the valence-shell excitations of hydrogen studied by high-resolution inelastic x-ray scattering

Synopsis Utilizing the high-resolution inelastic x-ray scattering technique, absolute inelastic squared form factors of four vibronic series belonging to the Bu , CΠu, EFg and B′ u electronic states of molecular hydrogen are determined experimentally. In addition, the same inelastic squared form factors are calculated by the multi-reference single and doubleexcitation configuration-interaction method for the Bu, CΠu, EFg. Apparent differences are observed between the present experimental results and all available calculated ones.