Multiple-Scattering Approach to Coherent Excitation in Electron-Capture Collisions

The complete density matrix for the $n=3\mathrm{}$ level of hydrogen coherently excited by electron capture, ${\mathrm{H}}^{+}+\mathrm{He}\to \mathrm{H}\mathrm{}(n=3\mathrm{})+{\mathrm{He}}^{+}$, at medium to high energies is calculated with the first Born approximation and for the first time with a multiple-scattering theory, namely the continuum distorted-wave approximation. Final-state interactions are also explicitly incorporated to account for the long-range coupling effects between the degenerate states of the projectile. Comparison is made with recent experimental data and a quasiclassical interpretation of coherences in terms of the orbital parameters of the captured electron is proposed.