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.
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