Adiabatic complex plane calculations of Rydberg states broadening by Rb and K perturbers

We use the adiabatic theory in the complex plane of internuclear distance to calculate the Rydberg states broadening cross sections in the ambient alkali-metal gases. We find that the imaginary part of the branch point between the relevant energy curves has an oscillatory structure which leads to a similar structure in the broadening cross section. The results are in very good agreement with the distorted wave diabatic perturbation theory for n < 30. However the adiabatic approach fails for higher n