Resonances in Systems Involving Positrons

When an incident particle on a target gets attached to the target, the cross-section at that energy could be much larger compared to those at other energies. This is a short-lived state and decays by emitting an electron. Such states can also be formed by the absorption of a photon. Such states are below the higher thresholds and are called autoionization states, doubly excited states, or Feshbach resonances. There is also a possibility of such states to form above the thresholds. Then they are called shape resonances. Resonances are important in the diagnostic of solar and astrophysical plasmas. Some methods of calculating the resonance parameters are described and resonance parameters occurring in various systems are given.

Unveiling shape resonances in H + HF collisions at cold energies

By aligning the reactant's rotational angular momentum it is possible not only to enhance or to diminish the intensity of the resonance, but also to split the resonance peak, disentangling the underlying contributions to the resonance pattern.