A photoelectron spectroscopy study of the valence shell photoionization dynamics of acetylene

The valence shell photoionization dynamics of acetylene were studied in the photon energy range 13-140 eV using photoelectron spectroscopy and synchro tron radiation. Photoelectron angular distributions and branching ratios we re determined for the X (2)Pi(u), A (2)Sigma(g)(+), B (2)Sigma(u)(+), C (2) Sigma(g)(+) single-hole ionic states and for inner valence correlation stat es. An interpretation of the experimental results was carried out based upo n previous theoretical predictions, and it appears that the photoionization dynamics are being strongly affected by shape resonance phenomena. The pho toelectron asymmetry parameters associated with the A (2)Sigma(g)(+) and th e C (2)Sigma(g)(+) ionic states provide the first experimental confirmation of the predicted sigma(u) continuum shape resonance. (C) 1998 Elsevier Sci ence B.V. All rights reserved.