On the theory of collisions of atoms in Rydberg states with neutral particles

The theory of transitions between Rydberg states induced by thermal collisions, and of the broadening and shift of optical lines involving such states, is reconsidered. It is shown that the Fermi potential can be generalized in terms of the reaction matrix of the collision between a free electron and the neutral perturber. Adiabatic potential curves of the quasi-molecule are thus obtained in analogy with quantum defect theory. An adiabaticity criterion is proposed to distinguish between inelastic and quasi-elastic collisions. The scattering length approximation and JWKB wave-functions are used to obtain an approximate expression for cross-sections of quasi-elastic collisions (Δn = 0) for intermediate n values (n approximately 15-20). It is also shown that it is possible to explain the observed behaviour of the broadening and the shift of optical lines by noble gases and alkalis for intermediate or high n values