Absolute cross sections for electron capture into the $3p$ and $3d$ states of hydrogen have been measured for 10- to 100-keV proton impact on He, Ne, Ar, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and ${\mathrm{O}}_2$. Improved $3s$ cross sections are presented for these gases from 10 to 120 keV. An apparent maximum in the $3p$ cross section occurs in this energy range for all gases. The $3d$ cross sections decrease monotonically with increasing impact energy according to an $\exp [-{\left(\frac{E}{K}\right)}^{\frac{1}{2}}]$ relationship, where $E$ is the impact energy and $K$ is a constant, with the exception of helium which shows a maximum in the $3d$ cross section between 15 and 20 keV. The value of $K$ is identical for all the diatomic gases. Balmer-$\alpha$ cross sections are synthesized from these results. Polarization of the $3d\to 2p$ radiation is reported.

• Received 29 September 1969

DOI:https://doi.org/10.1103/PhysRevA.1.1424