Measurement of cross sections for electron capture inton=3states of hydrogen

We have measured the cross sections for electron capture into the n=3,L,$M_L$ states of hydrogen for protons colliding with helium atoms at energies between 30 and 80 keV. We used a microwave-resonance, optical detection technique, in which a microwave field drives transitions within the n=3 manifold of the hydrogen atoms, and the change in the Balmer-α light emitted in the decay of the excited atoms is observed. The analysis included cascade feeding of the n=3 states by higher n states. The measured cross sections decrease as the angular momentum L increases, and for fixed L they decrease as ‖$M_L$‖ increases. The 3p and 3d cross sections are roughly inversely proportional to the square of the energy over this range of energies, whereas the 3s cross section peaks near 50 keV.