Influence of the linear Stark effect on electron capture into fully stripped ions

The complete density matrix for electron capture into the hydrogenic $n=2\mathrm{}$ projectile level is calculated within a modified Oppenheimer-Brinkmann-Kramers approximation which analytically takes into account the long-range coupling effects between the degenerate states of the projectile. The incorporation of the post-collisional Stark effect removes the shortcoming of the first-order calculations of relative $l$ cross sections and of the alignment. We find reasonable agreement between the calculated $s-p$ coherence and the data of Sellin et al. The experimentally observed shift of the coherent signal can be explained by the transient inhomogeneity of the external electric field.