Abstract
Positron annihilation on many molecules occurs via positron capture into vibrational Feshbach resonances, with annihilation rates often further enhanced by energy transfer to vibrational excitations weakly coupled to the positron continuum. Data presented here uncover another scenario in which the positron couples directly to a quasicontinuum of multimode vibrational states. A model that assumes excitation and escape from a statistically complete ensemble of multimode vibrations is presented that reproduces key features of the data.
Highlights
Positron annihilation on many molecules occurs via positron capture into vibrational Feshbach resonances, with annihilation rates often further enhanced by energy transfer to vibrational excitations weakly coupled to the positron continuum
Where ! is the vibrational mode energy and "b is the positron-molecule binding energy. The observation of these vibrational Feshbach resonances (VFRs) indicates that the molecule can form a bound state with a positron. The magnitudes of these VFRs are often further enhanced by intramolecular vibrational energy redistribution (IVR)
Simple theoretical estimates for VFRs and IVR-enhanced VFRs appeared to be incapable of explaining the magnitudes of the observed rates
Summary
Positron annihilation on many molecules occurs via positron capture into vibrational Feshbach resonances, with annihilation rates often further enhanced by energy transfer to vibrational excitations weakly coupled to the positron continuum. The annihilation rates as a function of incident positron energy " exhibit vibrational Feshbach resonances (VFRs) (e.g., populated via excitation of infrared-active modes) [1].
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