Electron energy-loss study of superexcited hydrogen molecules with the coincidence detection of the neutral dissociation

The electron energy-loss spectra of H 2 have been measured in coincidence with the neutral dissociation leading to H(1s)+H(2p) near the first ionization potential at the electron impact energy of 150 eV and the scattering angles of 2 degrees and 10 degrees , and compared with ordinary electron energy-loss spectra. The two spectra, the coincident and the ordinary ones, are similar to each other in shape below the energy level of H 2 + (X 2 Sigma g + , upsilon i =1), while they are different from each other above this energy level. Such a large change around upsilon i =1 is discussed in terms of the dynamics of superexcited hydrogen molecules, and the availability of this method for such studies is examined.