Spectroscopy of acetylene Rydberg states studied by VUV absorption and (3+1)-resonantly enhanced multiphoton ionisation

The ungerade ns + nd Rydberg states Of C2H2 converging to the ground state of the C2H2+ cation have been investigated in the energy range 74000-88000 cm(-1) by (3 + I)-multiphoton ionisation (REMPI) and by VUV absorption spectroscopy at the Super-ACO synchrotron radiation facility. Both methods have allowed the selective analysis of the Rydberg transitions with rotational resolution. Mulliken's semi-united atom model, in which predissociation has been taken into account, was used to understand the relative three-photon intensities among the different electronic transitions within the same Rydberg supercomplex. Lifetimes have been evaluated and illustrate very different behaviours towards predissociation for the observed Rydberg states. To cite this article: S. Boye et al., C R. Physique 5 (2004). (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.