Mitio Inokuti

Influence of Energy Transfer by the Exchange Mechanism on Donor Luminescence

The decay of donor luminescence in a rigid solution when modified by electronic energy transfer by the exchange mechanism is treated theoretically. The rate constant for the elementary process of energy transfer is taken to be of the Dexter form, const exp(−2R/L), where R is the donor—acceptor distance and L is a positive constant. Calculations are made of the yield and decay time of the donor luminescence as functions of the acceptor concentration. The resulting relationship among the above quantities enables one to analyze experimental data in a quantitative manner, and thereby to obtain information about an intermolecular exchange interaction. As an example of such an analysis, Ermolaevs data on triplet—triplet transfer between some aromatic molecules are compared with our results, and very good agreement is found with a choice of the single parameter L.

Electron inelastic-scattering cross sections in liquid water

Electron inelastic-scattering cross-section data for use as input in electron track-structure calculations in liquid water are re-examined and improved. The dielectric-response function used in such cross-sections is estimated on the basis of optical data and other experimental and theoretical information. The mean excitation energy for stopping power is obtained to be 81.8 eV. which is close to the recent experimental value. 79.75 + 0.5 eV, of Bichsel and Hiraoka. Inelastic-scattering cross sections are evaluated within the first Born approximation. Electron-exchange effects and semi-empirical corrections to account for non-Born effects at low energies are also incorporated.

Inelastic-collision cross sections of liquid water for interactions of energetic protons ☆

Abstract Cross-section data for inelastic interactions of energetic protons with liquid water, for use, e.g. as input in track structure analysis, are derived for an energy range from 0.1 keV to 10 GeV. At proton kinetic energies above about 500 keV, the first Born approximation and the dielectric-response function determined earlier are used. At proton energies above several hundred MeV in particular, the Fermi-density effect is also incorporated. At energies below about 500 keV, which corresponds to a residual range of about 8.9 × 10 −6 m, cross-section values are derived semi-empirically by an extensive and critical analysis of experimental and theoretical information concerning not only cross sections for individual processes such as ionisation, excitation, and charge transfer but also stopping power and other relevant quantities. Spectra of secondary electrons resulting from ionising collisions are also presented. The analysis also includes considerations of phase effects on cross sections.

The Optical Properties of Metallic Aluminum

Publisher Summary It is noted that the optical properties of metallic aluminum are among the most widely measured and analyzed of any material. They are generally dominated by three practically nonoverlapping groups of electronic transitions corresponding to absorptions by conduction band, L-shell, and K-shell electrons. The two strong interband transitions of the conduction-electron spectrum in the crystalline material are a consequence of the parallel-band effect that occurs in almost free-electron polyvalent metals. In these materials the occupied and unoccupied conduction bands are effectively parallel over substantial regions of k space in the vicinity of high-symmetry planes parallel to the zone faces. The key factor in obtaining accurate values of the optical properties came from the discovery that aluminum could be sputtered or evaporated to form highly reflecting metal films.

Electronic relaxation in rare-gas solids: Ejection of atoms by fast charged particles☆

Abstract Recent experiments show that the sputtering yields for condensed-gas solids bombarded by fast ions are large, even after allowance for the small surface binding energies. These yields are related to the electronic excitation produced by the incident ions in constrast to yields for metals and semiconductors. To understand the measured yields for condensed rare-gas solids we examine the conversion of electronic energy to lattice, nuclear motion. Thermal-spike models indicate that about 10–20% of the electronic energy deposited must be converted to nuclear motion in the vicinity of the ion track within 10−11 s to account for the observed yields. It is the theme of the present article to point out that results and data from recent spectroscopic and luminescence studies show that this is indeed the case. On electronic excitation of these closed-shell, van der Waals solids, new covalent bonds form. These bonds cause significant lattice displacements and thus provide a mechanism for the electronic recombination. Relaxation to low-lying electronic states then occurs via repulsive potentials, by which means sufficient electronic energy is converted to nuclear motion to account for the observed ejection (sputtering) from these solids by fast light ions.

Quantum defect values for positive atomic ions

Abstract The asymptotic quantum defects, at the ionization limit, of s, p, d, and f atomic orbitals have been calculated in the Hartree-Slater approximation for all ionization stages of all ions with atomic number Z ⩽ 50.

VUV ABSORPTION AND ITS RELATION TO THE EFFECTS OF IONIZING CORPUSCULAR RADIATION

Elements of the physics of photoabsorption as well as of energy transfer from fast charged particles are discussed. Among the key notions there are oscillator‐strength spectra, quantum yields, and action spectra. Throughout the discussion, emphasis is put on the important role of soft X‐rays and VUV light as obtained from a synchrotron radiation source in the understanding of actions of ionizing radiations in general.

Total cross-sections for inelastic scattering of charged particles by atoms and molecules—VIII. Systematics for atoms in the first and second row☆

Abstract The Bethe theory gives an asymptotic formula for the total cross-section σ tot for inelastic scattering of fast charged particles. For a (structureless) particle of charge ze and (non-relativistic) velocity v , it is written as σ tot = 4 πa 0 2 z 2 ( R / T ) M tot 2 ln (4 c tot T / R ), where R is the Rydberg energy, a 0 is the Bohr radius and T= 1 2 mv 2 , m being the electron mass. Two quantities, M tot 2 and ln c tot , depend upon the internal dynamics of the atom. We have performed comprehensive calculations of these quantities for neutral atoms He through Ar by use of independent-particle models, and also have studied the influence of electron correlations for several atoms. Our calculations reveal certain systematics of M tot 2 and ln c tot as functions of the atomic number Z . Because M tot 2 is expressed as the ground-state expectation value of the squared sum of atomic-electron coordinates, the trend of M tot 2 follows the size of the atom, governed by its shell structure. The quantity ln c tot also varies with the atomic size, but within a fairly modest range. Hence, the variation of σ tot at fixed v from one atom to another is chiefly governed by M tot 2 .

Elastic scattering of fast electrons by atoms. I. Helium to neon

The total elastic scattering cross section for electrons on neutral atoms is evaluated in the first Born approximation via tabulated values of the form factors. The theoretical results are compared with experiment for helium, neon and lithium. For lithium, comparisons are also made with Glauber and polarized-Glauber models. A simple model is presented for low-energy total cross sections in lithium, and its predictions compared with experiment. Elastic differential cross sections for helium and neon are briefly discussed.

Mean excitation energies for the stopping power of atoms and molecules evaluated from oscillator-strength spectra

The mean excitation energy for the stopping power of matter, usually expressed by symbol I, is the only nontrivial material property in Bethe’s [Ann. Phys. 5, 325 (1930)] asymptotic stopping-power formula. It is therefore a crucial input for the evaluation of stopping power for swift charged particles. To calculate the I value of a material from its definition, it is necessary to know the oscillator-strength spectrum of the material in question over the entire range of the excitation energy. We evaluate the mean excitation energies of 32 atoms and molecules from the oscillator-strength spectra that were published by Berkowitz in 2002 [Atomic and Molecular Photoabsorption: Absolute Total Cross Sections (Academic, San Diego, 2002)]. We find that most of the present I values are consistent with those given in the literature. The I values of NO2, O3, and C60 in particular are evaluated in the present work. For buckminsterfullerene C60, an estimation of the I value is made also using the local-plasma approxima...