Very low energy electron-H(2p) interaction studied in H--rare-gas collisions by translation electron spectroscopy

Detached electron energy spectra have been observed in the forward direction for collisions of H- ions with helium, neon and argon gas targets at 4 keV. Specifically, the channel corresponding to H(2p) excitation has been examined by recording the electron energy distributions in coincidence with Lyman-α photons. Near the 0o observation angle, electrons with very low energy in the projectile frame (1<Ep<100meV) are observed that are kinematically shifted in the laboratory and which yield important information on the H(n = 2)-e- interaction near threshold. The spectra reveal, in addition to the well known 1Po shape resonance of H-, a cusp typical of convoy electrons which is attributed to the long range dipole interaction between H(n = 2) and an electron. In addition, weak structure near 4 meV above the H(2p) threshold could constitute further evidence in support of the existence of dipole oscillations. (author)