Semirelativistic $1s-2s$ excitation of atomic hydrogen by electron   impact
  In the framework of the first Born approximation, we present a semirelativistic theoretical study of the inelastic excitation ($1s_{1/2}\longrightarrow 2s_{1/2}$) of hydrogen atom by electronic impact. The incident and scattered electrons are described by a free Dirac spinor and the hydrogen atom target is described by the Darwin wave function. Relativistic and spin effects are examined in the relativistic regime. A detailed study has been devoted to the nonrelativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamic behavior of the DCS in the relativistic regime have been addressed. 
S. Taj, B. Manaut and L. Oufni
physics.atom-ph