1s-2s excitation of fast hydrogen atoms in collisions with atomic and molecular hydrogen

Cross sections for 1s-2s excitation of 2-25 keV hydrogen atoms in passage through H and H2 have been determined. A tungsten-tube furnace has been used to provide a target of highly dissociated hydrogen and fast H(2s) metastable atoms formed in the excitation process have been detected by recording the Lyman- alpha quench radiation induced by an electric field. Measured cross sections in H are found to be in generally poor accord with theoretical estimates.