The valence shell excitations of argon were investigated by an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500eV, and the transition multipolarities for the excitations of 3p→3d, 4d, 5s, and 5p were elucidated with the help of the calculated intermediate coupling coefficients using the COWAN code. The generalized oscillator strengths for the excitations to 3p5 (3d, 3d’), 3p5 (5p, 5p’), and 3p5 (5s, 4d) were measured, and the profiles of these generalized oscillator strength were analyzed. Furthermore, although the present experimental positions of the maxima for the electric-monopole and electricquadrupole excitations in 3p→5p are in agreement with the theoretical calculations [Amusia et al., Phys. Rev. A 67, 022703 (2003)], the generalized oscillator strength profiles show obvious differences. In addition, the experimental generalized oscillator strength ratios for the electric-octupole transitions in 3p→3d are different from the theoretical prediction calculated by the COWAN code.

The generalized oscillator strengths for the valence-shell excitations to 3p5 (4s, 4s') and 3p5 (4p, 4p') of argon were measured by an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500eV. The transition multipolarities for these excitations were elucidated with the help of the calculated intermediate coupling coefficients using the COWAN code. The generalized oscillator strength profiles for the electric dipole excitations to 3p5 (4s, 4s'), the electric quadrupole and monopole excitations to 3p5 (4p, 4p') were analyzed and their positions of the extrema were determined. Furthermore, the generalized oscillator strength of the electric quadrupole excitation in 3p→4p was determined and its profile is in general agreement with the theoretical calculations. However, the generalized oscillator strength profile of the electric monopole excitation in 3p→4p is different from the theoretical calculations.

optical oscillator strength density spectra for valence-shell excitations of HCl and HBr, as well as for Br-3d inner-shell excitations of HBr, have been determined by high-resolution electron-energy-loss-spectroscopy method in the dipole limit. Absolute optical oscillator strengths for the discrete transitions of HCl and HBr are reported and compared with the previous results determined by the photoabsorption method.

The generalized oscillator strengths for the valence-shell excitations to 2p5 3s, 2p5 3p, and 2p5 4s of neon were measured with an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500eV. The transition multipolarities for these excitations were elucidated with the help of the calculated intermediate-coupling coefficients using the COWAN code. The generalized oscillator strength profiles for the electric monopole, electric dipole, and electric quadrupole excitations were analyzed and their positions of the extrema were obtained. Furthermore, the experimental generalized oscillator strength ratios between the excitations to 2p5 4s[3/2]1 and 2p5 4s'[1/2]1 were determined and found to be in agreement with the calculated intermediate-coupling coefficient ratio.

The inner-shell excitation spectra of krypton 3d electrons were measured at scattering angles of 0° and 4° by a fast-electron energy-loss spectrometer at an incident energy of 2.5keV with an energy resolution better than 80meV. Some interesting optically forbidden transitions were observed and the natural widths of the optically allowed and optically forbidden transitions were analyzed. It shows that the natural widths for the resonances having the same core hole are nearly equal, no matter whether they are optically allowed, optically forbidden, or different members of a Rydberg series.

The dipole-forbidden transition of D1Δ←X1Σ+ of CO has been observed by a fast electron-energy-loss spectrometer at a large scattering angle of 7° and with an energy resolution of 60 meV. The energy levels and the relative intensity distribution of D1Δ, v'=9–25 have been determined, most of the results are reported for the first time.

The experimental and theoretical ratios of the generalized oscillator strength sGOSd for valence excitations of Ne, Ar, and Kr are presented. The excitation selectivity for fast electron impact is elucidated: the LS coupling singlet nature of the ground state selects the LS coupling singlet components from the intermediate coupling wave function of the excited state. According to this rule, the GOS's for some unresolved transitions were determined. Furthermore, this work provides an experimental method to determine the intermediate coupling coefficients of singlet components.

Absolute double differential cross section spectra of O2 at scattering angles of 0°, 2°, 4°, 6°, and 8° below 119 eV have been determined by the angle-resolved electron-energy-loss spectrometer at an incident electron energy of 2500 eV. Some features above the first ionization threshold stand out as the momentum transfer square K2 increases. Based on our experimental results and theoretical analysis, they are assigned to the optically forbidden Rydberg series of 2σu‾1(c4Σ‾u)npσu 3Σ-g(n=2-6) and the inner-valence transition of (2σg)‾1(1πg)3 3Ⅱg←X3Σ‾g, respectively. Furthermore, the observed energy positions of 2σ‾1u(c4Σ‾u)npσu3Σ‾g(n=2–6) confirm a theoretical prediction [Zhong and Li, J. Phys. B 37, 735 (2004)] that the eigenquantum defects show an evident oscillation due to the presence of shape resonance.

The momentum transfer dependence of fundamental double excitation processes of helium is studied by absolute measurements using an angular resolved fast-electron energy loss spectrometer with high energy resolution. It elucidates the dynamical correlations, in terms of internal correlation quantum numbers, K, T, and A. The Fano profile parameters q, fa, p2, f, and S of doubly excited states 2(1, 0)2+ 1Se, 2(1, 0)2+ 1De, and 2(0, 1)2+ 1Po are reported as functions of momentum transfer K2. Qualitative analysis is given for the states of 2(-1, 0)2+ 1Se and 2(1, 0)2+ 1Se.