Charge Changing Collisions of Atomic Beams in Alkali-Metal Vapors. III. Formation of H(2s) Atoms from H⁺ Ions

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Formation of H(2s) atoms in charge exchange collisions of protons with Cs, Rb, K and Na atoms has been studied for the proton energy E ranging from 0.2 keV to 4.0 keV. The metastable atom fractions f_2s of neutral hydrogen H⁰ beams produced under single-collision condition, which is regarded as the ratio of ‘total’ cross section for the charge exchange reactions eventually leading to formation of H(2s) atoms to total charge exchange cross section, have been determined as a function of E. All of the f_2s(E) curves obtained exhibit a marked structure, and the f_2s(E) values vary between 0.18 and 0.38 with an average value of about 0.25 in this energy range. In the case of Cs target, the dependence of the yield of H(2s) atoms as well as the fraction f_2s on the target atom thickness in units of atoms/cm² has also been examined.