Zero-kinetic-energy photoelectron spectroscopy from the <i>A</i> 1<i>A</i> <i>u</i> state of acetylene: Renner–Teller interactions in the <i>trans</i>-bending vibration of C2H+2 <i>X</i> 2Π<i>u</i>

Abstract

Double-resonance excitation via the à 1Au state is used to record zero-kinetic-energy photoelectron spectra of acetylene. The analysis of these spectra leads to an improved value of 91 952±2 cm−1 for the adiabatic ionization potential to the C2H2+ X̃ 2Πu ionic ground state. Because the à 1Au intermediate state has a trans-bent geometry, transitions from it readily populate the trans-bending vibration of the ground state ion, leading to new information about this mode and its Renner–Teller interactions. The relative intensities of the Renner–Teller components and of the rotational structure within each component also provide information on the dynamics of the photoionization process.