Oscillator Strength Density Research Articles

Absorption Spectra of Some Liquids in the VUV

Absorption spectra and oscillator strengths have been determined for the liquids, benzene, toluene, hexafluorobenzene, tetramethylsilane, 2,2-dimethylbutane, and 2,2,4-trimethylpentane over a spectral range from 120 to 300 nm and compared with gas phase spectra. The effect of condensation manifests itself most obviously for transitions assigned to upper states of relatively large spatial extent or for transitions with a high spectral density of oscillator strength. Compensating effects, however, appear to mitigate the effect of condensation for both hexafluorbenzene and tetramethylsilane.

Physical significance of second electron-pair moments in position and momentum spaces

For many-electron atoms, the generalized electron-pair density function g(q;a,b) represents the probability density function for the magnitude |ari+brj| of two-electron vector ari+brj to be q, where a and b are real-valued parameters. It is pointed out that the second moments 〈q2〉(a,b), associated with g(q;a,b), are related with several physical properties such as the diamagnetic susceptibility χd, the form factor F(μ), the incoherent scattering function S(μ), the minus first moment M−1 of the oscillator strength density, and the dipole polarizability α. The corresponding moments 〈t2〉(a,b) in momentum space are connected with the mass polarization correction εM, the first moment M1 of the oscillator strength density, and the nuclear momentum squared 〈p02〉 as well as the electronic kinetic energy 12〈∑ipi2〉. The average excitation energy ΔE is also estimated from 〈q2〉(a,b) and 〈t2〉(a,b).

Comment on “Ab initio dynamic dipole polarizabilities for O2, its photoabsorption spectrum in the Schumann–Runge region, and long-range interaction coefficients for its dimer” [J. Chem. Phys. 109, 9802 (1998)

The oscillator-strength density calculated ab initio for the Schumann–Runge transition of O2 by Spelsberg and Meyer [J. Chem. Phys. 109, 9802 (1998)] is assessed against an up-to-date experimental database.

Optical Oscillator Strengths for 32S → 42P and 32S → 52P Excitations of Na

The electron-energy-loss-spectrum of sodium has been measured in discrete region at a 1.5 keV impact energy and a mean scattering angle of 0°. The relative optical oscillator strength density spectrum of the valence shell of sodium was established by using the dipole (e, e) method and then normalized to the theoretical optical oscillator strength of the 32S → 32P excitation. The optical oscillator strengths of the 32S → 42P and 32S → 52P excitations obtained in the present work are 0.014 ± 0.002 and 0.0026 ± 0.0004, respectively. Theoretical values of optical oscillator strengths for 32S → n2P (n = 3 - 5) excitations of sodium were obtained by using the relativistic configuration interaction method, which are 0.97, 0.012, and 0.0025, respectively.

Oscillator strengths for 3 [formula omitted]D– [formula omitted]F transitions of the lithium isoelectronic sequence

The nonrelativistic dipole-length, -velocity and -acceleration absorption oscillator strengths for the 1s 23d–1s 2 nf (4≤ n≤9) transitions of the lithium isoelectronic sequence up to Z=10 are calculated by using the energies and the multiconfiguration interaction wave functions obtained from a full core plus correlation (FCPC) method. In most cases, the agreement between the f-values from the length and velocity formulae is up to forth or fifth digits. Combining these discrete oscillator strengths with the single channel quantum defect theory (QDT), the discrete oscillator strengths for the transitions from 1s 23d state to highly excited levels ( n≥10) and the oscillator strength densities corresponding to the bound-free transitions are obtained.

Electronic structure and optical properties of neodymium monopnictides

The electronic structure and optical properties of neodymium monopnictides have been investigated. The linear muffin-tin orbital method in the atomic sphere approximation and the local density approximation to exchange and correlation in density functional theory has been used. The p–f mixing increases while f-band width decreases on going down the pnictogen column due to the increase in pnictogen size. The density of states at the Fermi energy increases on going from NdP to NdSb. The joint density of states and partial oscillator strength have been calculated. The optical conductivity at higher energy increases with the increase of pnictogen atomic number due to the increase in p→d and f→d oscillator strengths.

Oscillator strengths for 2 transitions of the lithium isoelectronic sequence

The nonrelativistic dipole-length, -velocity and -acceleration absorption oscillator strengths for the 1s22s-1s2np\(\) transitions of the lithium isoelectronic sequence up to Z=10 are calculated by using the energies and the multiconfiguration interaction wave functions obtained from a full core plus correlation (FCPC) method. In most cases, the agreement between the f-values from the length and velocity formulae is up to forth or fifth digit. Combining these discrete oscillator strengths with the single channel quantum defect theory (QDT), the discrete oscillator strengths for the transitions from the 1s22s state to highly excited levels (\(\)) and the oscillator strength densities corresponding to the bound-free transitions are obtained.

Oscillator strengths for 2

The nonrelativistic dipole-length, -velocity and -acceleration absorption oscillator strengths for the transitions of the lithium isoelectronic sequence up to Z=10 are calculated by using the energies and the multiconfiguration interaction wave functions obtained from a full core plus correlation (FCPC) method. In most cases, the agreement between the f -values from the length and velocity formulae is up to forth or fifth digit. Combining these discrete oscillator strengths with the single channel quantum defect theory (QDT), the discrete oscillator strengths for the transitions from the state to highly excited levels () and the oscillator strength densities corresponding to the bound-free transitions are obtained.

Recurrence spectroscopy of atoms in electric fields: Scattering in the presence of bifurcations

Closed-orbit theory gives a semiclassical formula for the photoabsorption oscillator strength density of atoms in external fields. The oscillator strength can be calculated from the properties of the classical orbits of the highly excited electron moving in the combined Coulomb and electric field. The deviation from the Coulomb potential due to an alkali-metal atom core causes scattering between the classical orbits when a closed orbit returns to the origin. Bifurcations of closed orbits happen when a focus moves through the origin and we present a theory that describes the scattering of the electron waves by the alkali-metal core for atoms in external electric fields in the presence of a bifurcation. @S1050-2947~98!03211-9# Highly excited electronic state atoms in external fields have become good testing grounds for the connection between quantum and semiclassical mechanics. They are amenable to both theoretical calculations and experimental measurement @1‐5#. Closed-orbit theory is a semiclassical theory which predicts the positions and amplitudes of peaks in the Fourier transform of the photoabsorption spectrum: The peaks are at the periods of classical orbits that go out and return to the nucleus; the amplitude depends on the divergence rate of the neighbors of the orbits @6,7#. Closed-orbit theory was developed for hydrogen in a magnetic field by Du and Delos @7#. It was applied to alkali-metal atoms in an electric field by Gao and Delos @8#. The general picture of closed-orbit theory, in which waves excited by the laser go out and are turned around in the external fields, was simple. There were, however, the usual problems that occur in any primitive semiclassical formula. The semiclassical approximation for the returning wave near the core could, and would, become infinite as a focus or caustic passed through the origin. These failures occur at the bifurcation energies where closed orbits are created or destroyed as the parameters controlling the classical dynamics vary @9‐12#. Uniform approximations to semiclassical wave functions which repair these failures have been developed in the chemical physics and mathematical literature @13‐15# and have become better known in atomic physics @16‐19#. The nonhydrogenic core of an alkali-metal atom can be treated semiclassically by either propagating trajectories through a model core potential @20# or by a scattering expansion in terms of hydrogenic closed orbits that are coupled together by the core @21#. The closed-orbit approach in Ref. @21# works well for highly excited states where the effective size of is small and one can partially avoid the neighborhood of bifurcations. It is an open question how to apply this theory near a bifurcation. We present a closed-orbit theory for scattering in alkali-metal atoms in the presence of bifurcations that occur in static electric fields. The theory can be generalized to handle other types of bifurcations in other static fields.

Theory of oscillator strength of the lithium isoelectronic sequence

Using the energies and the multiconfiguration interaction wavefunctions obtained from a full core plus correlation method, the nonrelativistic dipole-length, -velocity and -acceleration absorption oscillator strengths for the transitions are calculated. In most cases, the agreement between the f-values from the length and velocity formulae is up to the fourth or fifth digit. Our acceleration f-values also agree closely with the length and velocity f-values. Combining these discrete oscillator strengths with the single-channel quantum defect theory, the discrete oscillator strengths for the transitions from the state to highly excited levels and the oscillator strength densities corresponding to the bound-free transitions are obtained.

Dense plasmas, screened interactions, and atomic ionization

There now exist many laboratory programs to study non-equilibrium plasmas in which the electron interparticle spacing n e −1/3 is no more than a few Bohr radii. Among these are short-pulse laser heating of solid targets, where n e∼10 23 cm −3 , and inertial confinement fusion experiments, where n e>10 25 cm −3 can be achieved. Under such extreme conditions, the plasma environment is expected to have a strong influence on atomic energy levels and transitions rates. Investigations of atomic ionization in hot, dense plasmas have been motivated by the fact that the instantaneous degree of ionization is a key parameter for the modeling of these rapidly evolving physical systems. Although various theoretical treatments have been presented in the literature, here we focus on the “random field” approach, because it can readily incorporate (quasi-static) level shifts of the target ion as well as dynamic plasma effects. In this approach, the stochastic perturbation of the target by plasma density fluctuations is described in terms of the dielectric response function. Limiting cases of this description yield the familiar binary cross-sectional model, static screening collision models, and the more general dynamical screening models. Screening of the target ion is treated here with several static screening potentials, and bound state level shifts of these potentials are explored. Atomic oscillator strength densities based on these different models are compared in numerical calculations for ionization of He + and Ar +17. Finally, we compile a list of atomic/plasma physics issues that merit future investigation.

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.

Absorption and electrochemical properties of ruthenium(II) dyes, studied by semiempirical quantum chemical calculations

The electronic properties of Ru-polypyridine dyes were investigated by means of semiempirical calculations. Inlermediate neglect of differential overlap (INDO)/S including configuration interaction (CI) was used to calculate electronic density of state (DOS) structures, transition energies and oscillator strengths. Results for electronic transitions and HOMO energies were compared to absorption spectra and oxidation potentials. The carboxylated form of cis-bis(2,2′-bipyridine)bis(isothiocyanato)-ruthenium(II) is an efficient sensitizer in nanos-tructured photoelectrochemical solar cells. The calculation on this dye reveals a different electronic structure for this complex compared to the other Ru-polypyridine complexes. In this complex, the spatial distribution of the highest occupied molecular orbital is shifted towards the NCS ligands and the electronic transition lowest in energy is assigned to a RuNCS-bpγ(π *) charge transfer transition.

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.

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.

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.

STRUCTURE AND OSCILLATOR STRENGTH DENSITIES NEAR LⅡ,Ⅲ EDGES OF ARGON

The high resolution fast electron energy loss spectrum for inner shell 2p electron excitation and ionization of argon has been measured in present work at an electron impact energy of 2500eV and a mean scattering angle of 0°. The ionization limits and effective quantum numbers have been- deduced.- The oscillator strength densities for discrete transitions and two ionization continua were- also- determined.

INELASTIC COLLISION PROCESS OF Rb ATOM BETWEEN INITIAL AND FINAL CHANNELS

Based on the quantum defect theory, the infinite Rydberg states and its adjacent continue states with the same angular moment property will form a channel. Previous studies have considered the collision-induced transitions from a single initial state to a final channel. Here we extend these thoery to include all possible transitions between two channels. By defining a renormalized generalized oscillator strength density (GOSD) which varies smoothly across threshold, the inelastic collisions from an initial channel to a final channel can be treated in a unified manner. As an example, we present the renormalized GOSD of the Rb atom from s-initial to p-final channel, and also from s-initial to s-final channel.

Optically stimulated intersubband absorption in undoped amorphous Si/SiO2 qiantum well

AbstractIntersubband absorption has been observed in undoped amorphous multiple‐quantum‐well (MQW) strucctures under interband excitation. The transitions take place between the first and second subbands of the conduction band and involve non‐equilibrium electrons excited into the first subband by optical pumping. The absorption band FWHM of 0.1 eV is much larger than for crystalline MQWs, a fact which reflects the relaxation of the electron momentum conservation in the QW plane. The high joint density of states and oscillator strength for the intersubband transitions in amorphous QWs allow one to observe the absorption at low electron concentrations (Ne ≈ 1013 cm−3) in the ground conduction subband.