Absolute Optical Oscillator Strengths Research Articles

Optical oscillator strengths of the vibronic excitations of molecular deuterium determined by the dipole ( γ , γ ) method

Absolute optical oscillator strengths of the Lyman and Werner bands of molecular deuterium are determined by a $\mathrm{dipole}(\ensuremath{\gamma},\ensuremath{\gamma}$) method with the high energy resolution of 25 meV. A comprehensive comparison shows that an excellent agreement between the present experimental results and the earlier theoretical calculations is achieved for both Lyman and Werner bands. In addition, the electronic transition dipole moments of ${\mathrm{D}}_{2}$ are derived. The absolute optical oscillator strengths of the Lyman and Werner bands of ${\mathrm{D}}_{2}$ reported in this work can serve as the benchmark to test calculations with different theoretical models and calculational codes and, also, be used in thermonuclear fusion plasma and other fields.

Optical oscillator strengths of the valence-shell excitations of atoms and molecules determined by the dipole (γ,γ) method

The dipole (γ,γ) method, which is the inelastic X-ray scattering operated at a negligibly small momentum transfer, has been developed to determine the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules. This new method is free from the line saturation effect, and its Bethe-Born conversion factor varies much more slowly with the excitation energy than that of the dipole (e, e) method. Thus the dipole (γ,γ) method provides a reliable approach to obtain the benchmark optical oscillator strengths of the valence-shell excitations for gaseous atoms and molecules. In this paper, we give a review of the dipole (γ,γ) method and some recent measurements of absolute optical oscillator strengths of gaseous 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.

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

SynopsisThe dipole(γ, γ) method based on the inelastic x-ray scattering (IXS) technique is proposed and realized to measure the absolute optical oscillator strength (OOSs) for the valence-shell excitations of atoms and molecules. The OOSs of valence- shell excitations of helium are determined, and the good agreement with the previous results is observed.

Electronic excitation of carbonyl sulphide (COS) by high-resolution vacuum ultraviolet photoabsorption and electron-impact spectroscopy in the energy region from 4 to 11 eV.

The electronic state spectroscopy of carbonyl sulphide, COS, has been investigated using high resolution vacuum ultraviolet photoabsorption spectroscopy and electron energy loss spectroscopy in the energy range of 4.0-10.8 eV. The spectrum reveals several new features not previously reported in the literature. Vibronic structure has been observed, notably in the low energy absorption dipole forbidden band assigned to the (4π←3π) ((1)Δ←(1)Σ(+)) transition, with a new weak transition assigned to ((1)Σ(-)←(1)Σ(+)) reported here for the first time. The absolute optical oscillator strengths are determined for ground state to (1)Σ(+) and (1)Π transitions. Based on our recent measurements of differential cross sections for the optically allowed ((1)Σ(+) and (1)Π) transitions of COS by electron impact, the optical oscillator strength f0 value and integral cross sections (ICSs) are derived by applying a generalized oscillator strength analysis. Subsequently, ICSs predicted by the scaling are confirmed down to 60 eV in the intermediate energy region. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of carbonyl sulphide in the upper stratosphere (20-50 km).

Ab initio study of low-lying excited states of HCl: Accurate calculations of optical valence-shell excitations

We present accurate ab initio potential energy surfaces and dipole transition moments of numerous low-lying states of HCl in a large range of internuclear distances. Using these results, we computed the visible/ultra-violet absorption spectrum of HCl covering the energy range up to the first ionization potential and the absolute optical oscillator strengths for the first discrete electronic transitions. Comparison of these theoretical results is done with the available experimental and theoretical data. Finally, we present a complete peaks-attribution of the HCl electronic absorption spectrum. Our results are in good agreement with the available experimental results.

Optical oscillator strengths for valence-shell and Br-3d inner-shell excitations of HCl and HBr

Absolute 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.

Fast-electron-impact study on excitations of4p,4s,and3delectrons of krypton

Absolute optical oscillator strength densities for the excitations of the electrons $4p,$ $4s,$ and $3d$ have been measured. Their absolute optical oscillator strengths have also been obtained. An enhancement above the $4p$ ionization threshold in the photoabsorption spectrum was assigned as a delayed maximum which arises from the photoionization process of $4\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\epsilon}d$ according to present Dirac-Slater calculation. In the energy region of $4s$ autoionization, we have observed several features that are absent in previous fast-electron-impact work, but exist in optical measurements. We clarify this discrepancy here. Two Rydberg series of optically forbidden transitions, i.e., ${4s}^{\ensuremath{-}1}{ns(}^{1}S)$ $(n=5,6,7)$ and ${4s}^{\ensuremath{-}1}{nd(}^{1}D)$ $(n=4,5,6,7)$ have been observed when the spectrometer worked at conditions with larger momentum transfers, namely, ${K}^{2}=0.23$ a.u. and 0.67 a.u. Furthermore, the absolute optical oscillator strengths for the $3d$ excitation have been obtained.

Experimental and theoretical investigations of absolute optical oscillator strengths for valence excitations of nitric oxide

The absolute optical oscillator strength density spectra of nitric oxide in the energy region of 5.0-22.0 eV have been measured by a high-resolution fast-electron energy loss spectrometer. With the calculated results obtained by the multiscattering self-consistent-field method and channel characteristics, the strongly overlapped spectra in the energy region of 7.5-9.3 eV have been analysed and the corresponding partially vibrationally resolved optical oscillator strengths have been estimated from the experimental spectra.

Evaluation of absolute optical oscillator strengths for transitions from the A-state to the np Rydberg series in NO

We describe a method for calibrating oscillator strengths for transitions of a molecule from the A-state to the Rydberg states with the absolute scale for the transition from the A-state to the ground state. Two-colour resonant four-wave mixing spectroscopy has been used to record the spectra for the NO transitions from the A 2 Σ + ( υ′=0) state to both the vibrationally excited X 2 Π 3/2 ( υ″=8) electronic ground state and to the high Rydberg series at the same time. By comparison with the normalised relative signal intensities, absolute oscillator strengths for the transitions from the A-state to the n p 2 Π + Rydberg series have been evaluated based on the knowledge of this parameter for the NO γ band system.

Optical oscillator strengths and angular variation of intensity distributions within the Lyman and Werner bands of molecular hydrogen

Abstract The absolute optical oscillator strength density spectrum in the valence excitation region of molecular hydrogen was established at an impact energy of 1500 eV and a mean scattering angle of 0°. The absolute optical oscillator strengths for the vibrational transitions of the Lyman and Werner bands were determined. Meanwhile, intensity distributions within the Lyman and Werner bands were initially measured at the same impact energy but different scattering angles within 0.0–4.0°. All these experimental results were compared with appropriate previously-published data.

A STUDY OF OPTICAL OSCILLATOR STRENGTHS AND DIFFERENTIAL CROSS SECTIONS IN THE DISCRETE REGION OF CARBON MONOXIDE

The absolute optical oscillator strength density spectrum of carbon monoxide has been measured at an impact energy of 1.5keV and a mean scattering angle of 0° in an energy region of 7—21eV with typical FWHM 60meV. The absolute optical oscillator strengths corresponding to vibrational levels of A1Π,B1Σ+，C1Σ+ and E1Π are determined and compared with previous experimental and theoretical results. The reason why discrepancies exist among experimental results obtained by various methods has been explained and the limitation of dipole (e,e) method in determining optical oscillator strengths has been discussed.

Electron-impact study for the and ( n = 3 - 6) excitations in helium

Differential cross sections and generalized oscillator strengths for the and = 3 - 6) excitations overlapping neighbour non-dipole excitations in helium have been measured by an angle-resolved electron energy loss spectrometer at an impact energy of 1500 eV in a scattering angular range of . These data are first reported at such a high impact energy. Integral cross sections for the above (n = 3 - 6) excitations were also determined. Meanwhile, the absolute optical oscillator strength density spectrum in the valence region of helium was established at the same impact energy in a mean scattering angle of , and the absolute optical oscillator strengths for these discrete transitions corresponding to the valence region of helium are reported. All these experimental results are compared with previous appropriate published data.

High-resolution dipole (de, de) study for optical oscillator strengths of valence shell excitation of nitrogen

NITROGEN is the most abundant element in the earth’s atmosphere. The study of optical oscillator strengths of nitrogen is of great significance in atmosphere physics, space physics and environment science. These results are also used in many fields, such as fusion plasma and developments of the nitrogen laser. As we know, calculation of absolute optical oscillator strengths of molecular nitrogen are still at the level of electronic rather than vibronic states resolved. So

Electron-impact study in the valence and autoionization resonance regions of neon

The recently built electron-energy-loss spectrometer (EELS) (typical full width at half maximum of 60 meV) has been employed to measure EELS spectra of neon in discrete and autoionization resonance regions at a 2.5 keV impact energy and a mean scattering angle of 0\ifmmode^\circ\else\textdegree\fi{}. Relative optical oscillator strength density spectra were established by multiplying the EELS spectra by the known Bethe-Born conversion factor of the spectrometer, and then were normalized at a single point in the smooth continuum. Absolute optical oscillator strengths corresponding to these energy regions are reported and compared with previously published experimental and theoretical values. Two forbidden transitions in the autoionization region are observed and identified. One of them has not been previously reported to our knowledge.

Absolute generalized oscillator strengths for the vibronic bands ofA1Π,B1Σ+,C1Σ+, andE1Π transitions of carbon monoxide

Generalized oscillator strengths for the vibronic bands of ${\mathrm{A}}^{1}$\ensuremath{\Pi}, ${\mathrm{B}}^{1}$${\mathrm{\ensuremath{\Sigma}}}^{+}$, ${\mathrm{C}}^{1}$${\mathrm{\ensuremath{\Sigma}}}^{+}$, and ${\mathrm{E}}^{1}$\ensuremath{\Pi} have been determined by an angle-resolved electron energy loss spectroscopy at an incident electron energy of 1500 eV and in an angular range of 0.5\ifmmode^\circ\else\textdegree\fi{}--6.0\ifmmode^\circ\else\textdegree\fi{}. The corresponding absolute optical oscillator strengths obtained by extrapolating the generalized oscillator strengths to ${\mathrm{K}}^{2}$=0 are also reported. The present results have been compared with previous work, and some differences between them have been explained. The experimental generalized oscillator strengths for ${\mathrm{v}}^{|\mathrm{I}\mathrm{H}}$=0--8 of ${\mathrm{A}}^{1}$\ensuremath{\Pi}, ${\mathrm{v}}^{|\mathrm{I}\mathrm{H}}$=0--1 of ${\mathrm{B}}^{1}$${\mathrm{\ensuremath{\Sigma}}}^{+}$, ${\mathrm{C}}^{1}$${\mathrm{\ensuremath{\Sigma}}}^{+}$, and ${\mathrm{E}}^{1}$\ensuremath{\Pi} are reported.

A STUDY OF OPTICAL OSCILLATOR STRENGTHS-FOR VALANCE SHELL OF MOLECULAR OXYGEN

The absolute optical oscillator strength density spectrum of oxygen has been measured at an impact energy of 1.5 keV and a mean scattering angle of 0° in an energy region of 5.7—28.5 eV with typical FWHM 60 meV.The absolute optical oscillator strengths corresponding to vibrational levels of E3Σ-ｕ,ν′=0,1,2 and 23Πｕ,ν′=0,1 are reported and compared with previous experimental and theoretical results.The validity and accuracy of the Bethe-Born conversion factor is confirmed down to 6 eV by comparison.

Discrete and continuum photoabsorption oscillator strengths for the electronic spectrum of nitrous oxide (5.5–203 eV)

The electronic excitation spectrum and the associated absolute optical oscillator strengths for the photoabsorption of nitrous oxide in the energy region 7.4–203 eV have been obtained using low-resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. High-resolution dipole (e, e) spectroscopy (0.048 fwhm) has been used to measure the absolute photoabsorption oscillator strengths in the valence shell discrete region in the energy region 5.5–30 eV. The present results are compared with previously reported experimental and theoretical data.

The electronic spectrum of water in the discrete and continuum regions. Absolute optical oscillator strengths for photoabsorption (6–200 eV)

The electronic excitation spectrum and the associated absolute optical oscillator strengths for the photoabsorption of water have been determined in the energy region 6–200 eV using low resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. In addition, detailed studies of the absolute photoabsorption oscillator strengths for the valence shell discrete electronic transitions of water have been made using high resolution dipole (e, e) spectroscopy (0.048 eV fwhm), from the first excitation threshold up to 30 eV. The present results are free of “line saturation” (i.e. bandwidth/linewidth interaction) effects which can lead to serious errors when absolute intensity measurements are made using conventional Beer-Lambert law photoabsorption methods.