Charge transfer into the metastable 2S level of hydrogen by protons colliding with K and Na

We measure the charge transfer cross section for protons in potassium and sodium with the final state being H(2s)+A⁺. Using a crossed-beam experimental method we look at this cross section as a function of proton beam energy from 500 to 2500 eV. Our results for potassium agree with previous experiments and theories in showing two main peaks in the cross section: one of (3.9 ± 1.5)× 10^-15 cm² at a proton beam energy of 800 eV, and another of (2.8± 1.1)× 10^-15 cm² at a proton beam energy of 2.5 keV. Our results for sodium show a steadily rising cross section with a value of (7.3± 2.5)× 10^-15 cm² at a proton beam energy of 2.5 keV in agreement with the prediction of Kubach and Sidis; we do not find the maximum at 700 eV reported by Nagata that agrees with the theory of Kimura, Olson, and Pascale.