Dissociative photoionisation of H2: proton kinetic energy spectra

Abstract

The kinetic energy spectra of the protons produced in the dissociative photoionisation of H₂ and directed predominantly along the electric vector of a photon beam have been obtained at certain wavelengths between 19.8 and 40.8 eV. The time-of-flight method described employed a specially constructed wide aperture analyser with multichannel analysis to extract the very weak signals available. The system has been used to measure the energy distributions of the protons formed through the ground state of H₂⁺ and at higher energies, where two-electron excited states of H₂ and other states of H₂⁺ also contribute to proton production. Protons identified with the lowest ¹ Sigma _u⁺ state (predominantly 2p sigma _u2s sigma _g) exhibit a peak in their kinetic energy distribution which appears to move to higher energies as the photon energy is increased. The contributions from direct and autoionising processes are assessed and related to other published results including electron impact data.