Spin dynamics in photon ionization processes in hydrogenic atoms

Abstract

Spin effects in hydrogenic atoms to relativistic order 1/c^2 have been considered and modeled in three different gauges, two of which have been used extensively in the dipole approximation to calculate cross sections in photon ionization processes in the perturbative limit. It has been found that spin effects are small in the perturbative limit, though it has been discussed as to why this might not be the case in the non-perturbative limit. Further, a asymmetry in spin terms between the velocity gauge and the length gauge has been found.