Collision Processes of Highly Excited Hydrogen Atom. I. Transitions between Degenerate States

The cross sections for the transitions 5 S 1/2 →5 P 1/2 , 5 S 1/2 →5 P 3/2 , 5 P 1/2 →5 D 3/2 , 5 S 1/2 →5 D 3/2 and 5 S 1/2 →5 D 5/2 in the hydrogen atom by proton impact are calculated on the basis of the impact parameter method. Distant collisions are dominant and the couplings among the sub-levels belonging to the same n are important at low energies, but the couplings with the levels belonging to different n 's are negligibly small. The Glauber and the Born approximations are also applied to the same problem and the Glauber approximation gives a good agreement with the impact parameter method over a wide energy range down to at least about 100 eV.