Collisions of Rydberg Atom with Neutral Particles: Weak-Coupling Models

Abstract

In the present chapter we start the consideration of collisions involving the Rydberg atoms and neutral particles. Within the framework of the weak-coupling approximations we present general techniques for calculation of transition probabilities and cross sections between highly excited states and ionization induced by scattering of the quasi-free Rydberg electron by a neutral target. Theoretical description of these collisions will be based on two approaches, outlined in the preceding chapter. The first one is the semi-classical time-dependent approach in the impact-parameter representation combined with the first-order perturbation theory. It deals directly with the potential of the electron-perturber interaction. To derive analytic formulas for probabilities and cross sections and to demonstrate their dependencies on the main physical parameters this interaction will be described by the Fermi pseudopotential of the zero-range. The second approach based on the impulse-approximation will allow us to express the cross section of the Rydberg atom-neutral collisions in terms of the amplitude f _eB(k′, k), differential dσ _eB (k, θ)/dΩ or total σ _eB(k) cross sections for scattering of the free electron by the perturbing atom or molecule. It will provide the general treatment of the Rydberg atom-neutral collisions within the framework of the quasi-free electron model and will be valid for any arbitrary form of the electron-perturber scattering amplitude.