Electron loss and de-excitation of 5-500 keV metastable hydrogen atoms in passage through gas targets

The collisional destruction of 5-500 keV 2s metastable hydrogen atoms in passage through H 2 , He, Ar, Kr and N 2 has been investigated using a modulated beam technique. Cross sections sigma 2s.1 for one-electron loss and total cross sections sigma D for all collisional destruction processes have been separately determined. Electron capture leading to negative ion formation is found to be relatively unlikely at the highest energies considered sigma 2s.1 approximately= sigma D . Cross sections for de-excitation sigma 2s.1s approximately=( sigma D - sigma 2s.1 ) increase in relative importance with decreasing impact energy. Values of both sigma 2s.1s and sigma D for H 2 and He agree with estimates based on the first Born approximation. The growth and equilibration of H(2s) atoms in electron capture by protons in H 2 , He, Ar and N 2 has also been investigated and interpreted quantitatively in terms of the relevant collision mechanisms.