PHOTOIONIZATION OF ACETYLENE NEAR THE THRESHOLD

The photoionization of C2H2 has been studied by threshold photoelectro n (TPE) spectroscopy and constant photoelectron energy (CPE) spectrosc opy in the energy region between 11.3 and 20 eV, TPE spectroscopy has enabled a detailed observation of the first three electronic states of the ion as well as the non-Franck-Condon region. Further investigatio n by CPE spectroscopy at photoelectron energies between 0.2 and 3.7 eV has established that the main process occurring in this region is the autoionization of superexcited states of C2H2. A dynamic effect in th e autoionization process has been proposed to explain the excitation o f a quasicontinuum of vibrational levels of the ionic ground state in the region of 13 eV.