Vibrational Feshbach Resonances Mediated by Nondipole Positron-Molecule Interactions

TL;DR

This paper reports improved measurements of positron-molecule annihilation revealing vibrational Feshbach resonances involving nondipole interactions, expanding understanding beyond infrared-active modes.

Contribution

It provides experimental evidence of resonances linked to infrared-inactive vibrational modes, suggesting nondipole interactions can facilitate positron binding.

Findings

Resonances observed with cryogenic positron beam

Evidence of nondipole interaction involvement

Implications for theoretical models of positron binding

Abstract

Measurements of energy-resolved positron-molecule annihilation show the existence of positron binding and vibrational Feshbach resonances. The existing theory describes this phenomenon successfully for the case of infrared-active vibrational modes which allow dipole coupling between the incident positron and the vibrational motion. Presented here are measurements of positron-molecule annihilation made using a recently developed cryogenic positron beam capable of significantly improved energy resolution. The results provide evidence of resonances associated with infrared-inactive vibrational modes, indicating that positron-molecule bound states may be populated by nondipole interactions. The anticipated ingredients for a theoretical description of such interactions are discussed.