Collisions of Electrons with Hydrogen Atoms. V. Excitation of Metastable 2S Hydrogen Atoms

Ground-state hydrogen atoms produced by thermal dissociation in a tungsten furnace were excited by collision with electrons having energies up to 600 ev. Those atoms which were excited to the metastable $2S$ state were subsequently quenched in an electrostatic field, and the resulting Lyman-alpha radiation was detected with an iodine-vapor-filled photon counter. In order to assign absolute cross-section values to the excitation function obtained in this way, the ratio of the $2S$ to the $2P$ excitation cross sections was determined. From previously obtained knowledge of the cross section for excitation to the $2P$ state, the absolute $2S$ cross section was evaluated. Agreement with the Born approximation was observed at high energies. The angular distribution of the scattered $2S$ atoms was also investigated for electron energies up to 600 ev.