David M. Schrader

Principles and applications of positron and positronium chemistry

Introduction to positron and positronium chemistry, Y.C. Jean et al compounds of positrons and positronium, D.M. Schrader experimental techniques in positron spectroscopy, P.G. Coleman organic and inorganic chemistry of the positron and positronium, G. Duplatre and I. Billard physical and radiation chemistry of the positron and positronium, S.V. Stephanov and V.M. Byakov positrons and positronium in the gas phase, D.M. Schrader positron porosimetry, M.H. Weber and K.G. Lynn positron annihilation studies on superconducting materials, C.S. Sundar positronium in Si and SiO2 thin films, R. Suzuki applications to polymers, P.E. Mallon applications to coatings and paints, Y.C. Jean et al positron annihilation electrospectroscopy, S. Amdani et al characterization of nanoparticle and nanopore materials, J. Xu age momentum correlation (AMOC), H. Stoll et al.

Binding energies of positronium fluoride and positronium bromide by the model potential quantum Monte Carlo method

A method previously used by the authors in an accurate calculation of the binding energy of positronium chloride [Phys. Rev. Lett. 68, 3281 (1992)] is applied to positronium fluoride and positronium bromide. The binding energies obtained with this method are PsF, 1.98±0.17 eV; PsCl, 1.91±0.16 eV; PsBr, 1.14±0.11 eV.

Erratum: Fine‐Structure Studies of Diatomic Molecules: Two‐Electron Spin‐Spin and Spin‐Orbit Integrals

The two‐electron integrals that contribute to the spin–spin and spin–orbit interactions in diatomic molecules are evaluated for wavefunctions constructed from Slater orbitals. For arbitrary combinations of quantum numbers, expressions are derived in tensor–operator form for all the one‐ and two‐center Coulomb, hybrid, and exchange terms that occur. An attempt is made in the analysis to maximize compatibility with some of the previous treatments of interelectronic repulsion integrals.

DIFFUSION QUANTUM MONTE CARLO CALCULATION OF THE BINDING ENERGY AND ANNIHILATION RATE OF POSITRONIUM HYDRIDE, PSH

Using the diffusion quantum Monte Carlo (DMC) method with importance sampling, we calculate the binding energy and annihilation rate of positronium hydride, PsH. We get 1.0661±0.0014 eV for the binding energy, and 2.463±0.020 ns−1 for the annihilation rate. The binding energy is in agreement with the results of the best Ritz variational calculations and the best DMC calculation reported to date, and the annihilation rate agrees with the results of the Ritz variational calculations but not that of the only other DMC result known to us. A new method for correcting expectation values calculated from mixed estimators is proposed and demonstrated.

Bound states of positrons with atoms and molecules: Theory

Abstract Calculations of the binding energies and annihilation rates of bound atomic and molecular systems which contain a positron are reviewed. Emphasis is placed on methods of calculation and the quality of the numerical results. In this article we limit our attention to positrons interacting with atoms, diatomic molecules, and their ions.

Calculation of Spin—Spin Interaction Integrals

Integrals of dipolar interactions between electron spins in atoms and molecules calculated without approximation

Magnetic effects on positronium formation and annihilation in organic liquids

It was recently found that an external magnetic field markedly enhances the orthopositronium annihilation rate in certain organic solutions above and beyond that expected for the Zeeman effect. Several solutions have been studied, but the effect has been found only for nitrobenzene in n‐hexane. A mechanism for this is proposed and tested numerically with a kinetics scheme modified to include nonhomogeneous spur effects. The mechanism features the quenching of orthopositronium by a short‐lived triplet solute species, the concentration of which is moderated by the applied magnetic field.

Orbital following and hyperfine interactions in CH3

In a recent paper, Beveridge and Miller conclude that for the calculation of isotropic hyperfine interactions in simple planar hydrocarbon radicals, a semi-empirical molecular orbital method has some advantages over a semi-empirical valence bond method. In the present work we examine this conclusion and find that the arguments which support it are questionable. Our own critical comparison of the two methods does not lead to a clear conclusion. In addition, we report a method for calculating the degree of orbital following in a spin-unrestricted Hartree-Fock molecular orbital wave function and give numerical results for CH3 in its out-of-plane bending mode.

COMMENT ON: AB INITIO CALCULATION OF OH-; E+ SYSTEM WITH CONSIDERATION OF ELECTRON CORRELATION EFFECT J. CHEM. PHYS 101, 5925 (1994)

A calculation of the positronium affinity of the hydroxyl radical (equivalently, the binding energy of positronium hydroxide, PsOH), recently reported by Tachikawa et al., is in error because an incorrect value of the electron affinity of OH was combined with their calculated positron affinity of the hydroxide anion. When the correct value of the electron affinity of OH is used, the calculated binding energy of PsOH changes sign, and PsOH is predicted to be unstable to dissociation. Thus, the conclusion reported by Tachikawa et al., namely, that PsOH is stable, is not supported by their calculations.

Fragmentation and ionization of CH3F by positron and electron Impact

Abstract New data for the fragmentation of CH3F by low energy e+ using an improved spectrometer are presented. The positively charged fragment ions are detected and mass analyzed using a time-of-flight mass spectrometer and the ion yields are measured as a function of impact energy. For comparison, corresponding data have been obtained for e− scattering, using a similar apparatus.