Excitation to the $2s$ State of Hydrogen by 20- to 120-keV Hydrogen-Atom Impact on He, Ne, Ar, and ${\mathrm{N}}_2$

Absolute cross sections have been measured for the production of hydrogen atoms in the metastable $2s$ state by fast (20- to 120-keV) ground-state hydrogen-atom impact on He, Ne, Ar, and ${\mathrm{N}}_2$. The shape of the excitation curve for impact on He is not reproduced by the Bornwave calculation of Levy although the theory curve intersects the experimental curve near the two energy extremes. The scaled Born curves of Levy lie below the experimental curves for impact on Ne and Ar, although there is a general agreement near 20 keV for both gases. Experimental values for the cross sections for production of the $2s$ and the $2p$ states by hydrogen-atom impact on the four gases are presented in the range of 1-120 keV by combining and weighting the data of Birely and McNeal with the present data where they overlap.