Final-state interactions in the zero-kinetic-energy-photoelectron spectrum of H2

A rotationally resolved zero-kinetic-energy (ZEKE) photoelectron spectrum has been recorded for the lowest energy valence band of H₂. A coherent laser-based extreme ultraviolet (XUV) source, tuned from 128 200-128 900 cm^-1 excites the molecules to the ionization limit, and near-threshold electrons, in a narrow energy bandwidth (a few cm^-1 ) just below the ionization limit, are detected by field ionization as a function of laser wavelength. The rotational components for the H²₊X ²Σ⁺_g-H₂ X ¹Σ⁺_g (2-0) vibrational band show different relative intensities, compared to the conventional photoelectron spectrum and to the predictions of theoretical calculations. The perturbed intensities of the N⁺=0←J`=0 and the 0←2 rotational lines are shown to be attributable to an interaction of the pseudocontinuum of near-threshold N⁺=0 np J'=1 Rydberg states, with the interloper N⁺=2, 26p J'=1 state. The enhanced intensity of the 2←0 rotational line is attributable to a ``complex resonance'' involving the v⁺=3 R(0) 8p0 transition.