Dipole-allowed and dipole-forbiddenlchange in slow collisions ofNa+with Na(28d) Rydberg atoms

Both dipole-allowed and dipole-forbidden transitions occur in slow l-change collisions of ${\mathrm{Na}}^{+}$ with Na(28d) Rydberg atoms, despite the validity of the dipole approximation. Measurements of the velocity dependence of the final-state distribution under single-collision conditions are reported. Effects of strong coupling were found, in partial agreement with recent coupled-channel calculations. Microwave-resonance techniques were used to identify the selective-field-ionization signatures of 28f, g, and h states.