The collision-induced excitation of atomic hydrogen to the H(n =2) states in H+-Ne and H+-Ar collisions was measured in an energy range of 1 to 25 keV. From a polarization analysis of the emitted Lyman-alpha radiation as a function of an external electric field the partial cross sections sigma(lm) for excitation to the H(2s) and the H(2pm) magnetic substates (m = 0, +/- 1) and the real part of the s0-p0 coherence were extracted. For both collision systems an energy dependent forward-backward asymmetry corresponding to a shift of the centre-of-charge relative to the centre-of-mass (electric dipole moment) was observed. The collision-induced electric dipole moment (D(z)) is generally small or negative at incident energies below 10 keV and rises steeply towards higher energies. The present results are in reasonable agreement with own close-coupling calculations employing a molecular representation.