[Show abstract][Hide abstract] ABSTRACT: We analyse the process of rapid positron annihilation in large polyatomic molecules due to positron capture into vibrational Feshbach resonances. Resonant annihilation occurs in molecules which can bind positrons, and we analyse positron binding to alkanes using zero-range potentials. Related questions of spectra of annihilation gamma quanta and molecular fragmentation following annihilation, are discussed briefly.
The European Physical Journal D 01/2009; 518080(34):51-61. · 1.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Positrons can attach to molecules via vibrational Feshbach resonances, leading to very large annihilation rates. The predictions of a recent theory for this process are validated for deuterated methyl halides where all modes are dipole coupled to the incident positron. Data and analysis are presented for methanol and ethylene, demonstrating the importance of combination and overtone resonances and the ability of the theory to account for these features. The mechanism for these resonances and criteria for their occurrence as well as outstanding questions are discussed.
Physical Review A 01/2008; 77(6). · 3.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Enhanced positron annihilation on polyatomic molecules is a long-standing and complex problem. We report the results of calculations of resonant positron annihilation on methyl halides. A free parameter of our theory is the positron binding energy. A comparison with energy-resolved annihilation rates measured for CH3F, CH3Cl, and CH3Br [L. D. Barnes, Phys. Rev. A 74, 012706 (2006)10.1103/PhysRevA.74.012706] shows good agreement and yields estimates of the binding energies.
[Show abstract][Hide abstract] ABSTRACT: In this paper we use a zero-range potential (ZRP) method to model positron interaction with molecules. This allows us to investigate the effect of molecular vibrations on positron–molecule annihilation using the van der Waals dimer Kr2 as an example. We also use the ZRP to explore positron binding to polyatomics and examine the dependence of the binding energy on the size of the molecule for alkanes. We find that a second bound state appears for a molecule with ten carbons, similar to recent experimental evidence for such a state emerging in alkanes with twelve carbons.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 12/2005; · 1.19 Impact Factor