Angular momentum coherences in the differential capture amplitude in hydrogen

The differential capture amplitude for charge exchange from the hydrogenic ground state (1s) to an arbitrary final state (nlm) of hydrogen is calculated within the Coulomb-Brinkman-Kramers approximation in closed form. The result serves to determine orientation, alignment and s-p coherence as a function of the scattering angle theta . Applications to electron capture from the K shell of argon by fast protons and alpha particles are discussed. Coherences between substates provide a sensitive test for the validity of the semiclassical approximation.