Coherent excitation in electron capture collisions

We have calculated the coherent excitation cross sections induced in electron capture collisions with fast impinging ions, within the eikonal approximation taken in its prior form. The cross sections and components ϱ0k(l1, l2) of the irreducible tensor associated with the l1, l2 density matrix elements, are given in a closed analytical form, which yields directly the total intensity and the polarization. This result generalizes the one obtained by F.T. Chan and J. Eichler (Phys. Rev. A20 (1979) 1811) for electron capture into arbitrary nl shells. The sub-shell cross section values agree with those calculated within the Born approximation. The polarization — about 20% — is higher than that obtained in close coupling methods (i.e. H.G. Morrison and U. Opik, J. Phys. B11 (1978) 473). It is also higher than that measured in electron capture experiments with thin gas-cells.