Resonant dissociative photoionization of H2

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Abstract
The absorption of photons with an energy of 26.9 eV by H2 produces H+ ions with kinetic energies ranging up to 4.4 eV. We attribute the energetic H+ ions to absorption into a 1Σu+ resonance state of H2 which autoionizes into a continuum corresponding to a free electron moving in the field of the 1sσg core of H2+. We present calculations of the real and imaginary parts of the complex potential energy surface of the resonance state and of the transition dipole moment between the ground state of H2 and the resonance state. The resulting cross section for the production of energetic H+ ions and the calculated ratio of H+ to H2+ ions produced are in agreement with measurements. The energy distribution of the H+ ions has a maximum at about 3.2 eV. The maximum cannot be reproduced by a classical description of the nuclear motion in the autoionizing resonance state, but it does arise when a quantal treatment is used, in which the nuclear motion is governed by the real part of the complex potential.

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