Electron Impact Excitation of Hydrogen Lyman- α Radiation

An experimental investigation of electron impact excitation of the 2p state of atomic hydrogen is described. A beam of electrons was passed through a chopped beam of hydrogen atoms in a high vacuum apparatus. The modulated flux of Lyman-α photons emitted in the radiative decay of the 2p state was taken as a measurement of the excitation probability resulting from direct excitation plus indirect excitation resulting from cascading. The region surrounding the intersection of the two beams was electrically and magnetically shielded to prevent quenching of metastable 2s atoms and thereby to ensure that the observed Lyman-α flux resulted from decay of the short-lived 2p state. The experimental results are consistent with those obtained by Fite, Stebbings, and Brackmann [1959], and confirm the existence of a large discrepancy between theoretical and experimental results in the electron energy range below 50 eV.