Positron-molecule interactions: resonant attachment, annihilation, and bound states

Abstract

This article presents an overview of current understanding of the interaction of low-energy positrons with molecules with emphasis on resonances, positron attachment and annihilation. Annihilation rates measured as a function of positron energy reveal the presence of vibrational Feshbach resonances (VFR) for many polyatomic molecules. These resonances lead to strong enhancement of the annihilation rates. They also provide evidence that positrons bind to many molecular species. A quantitative theory of VFR-mediated attachment to small molecules is presented. It is tested successfully for selected molecules (e.g., methyl halides and methanol) where all modes couple to the positron continuum. Combination and overtone resonances are observed and their role is elucidated. In larger molecules, annihilation rates from VFR far exceed those explicable on the basis of single-mode resonances. These enhancements increase rapidly with the number of vibrational degrees of freedom. While the details are as yet unclear, intramolecular vibrational energy redistribution to states that do not couple directly to the positron continuum appears to be responsible for these enhanced annihilation rates. Downshifts of the VFR from the vibrational mode energies have provided binding energies for thirty species. Their dependence upon molecular parameters and their relationship to positron-atom and positron-molecule binding energy calculations are discussed. Feshbach resonances and positron binding to molecules are compared with the analogous electron-molecule (negative ion) cases. The relationship of VFR-mediated annihilation to other phenomena such as Doppler-broadening of the gamma-ray annihilation spectra, annihilation of thermalized positrons in gases, and annihilation-induced fragmentation of molecules is discussed.

50 pages, 40 figures

References in corpus (14)

• Positron annihilation spectrum from the Galactic Center region observed by SPI/INTEGRAL
• Positronic lithium, an electronically stable Li-e${}^{+}$ ground state
• Mechanisms of positron annihilation on molecules
• Positron-molecule annihilation by capture into vibrational Feshbach resonances of infrared-active modes
• Many-body theory of positron-atom interactions
• Calculation of the positron bound state with the copper atom
• Large dimension Configuration Interaction calculations of positron binding to the group II atoms
• Many-body theory of gamma spectra from positron-atom annihilation
• Positron scattering and annihilation from the hydrogen molecule at zero energy
• Positron-atom scattering using pseudo-state energy shifts
• Positron Annihilation on Polycyclic Aromatic Hydrocarbon molecules in the Interstellar Medium
• Generating phase shifts from pseudo state energy shifts
• Application of the zero-range potential model to positron annihilation on molecules
• Stability and production of positron-diatomic molecule complexes

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