Anomalous temperature effect on the broad asymmetric Franck-Condon photoelectron spectrum of theC10−monocyclic ring cluster

Abstract

Combining the first-principles electronic structure theory and time-dependent technique, we evaluate the vibrational structure in the photoelectron spectrum of ${\mathrm{C}}_{10}^{\ensuremath{-}}.$ This combination approach is exact within the Condon approximation and the harmonic-vibration model, i.e., it includes displacement, frequency change, and mode mixing (Duchinsky effect) of the vibrations between the initial and final charge states. The evaluation shows a broad asymmetric band shape, which is consistent with an experimentally measured spectrum. This asymmetric shape, which is common to the Franck-Condon spectra for quasistrong vibronic (vibration-electron) coupling, is found to be well fitted to a skewed Gaussian function. And, it has also been found that the asymmetry is increased as the temperature becomes high. On the contrary, the vibrational model taking into account only displacement, which is widely accepted in analyzing Franck-Condon spectra, always predicts a symmetric shape at high temperatures; therefore the temperature induced increase of asymmetry in the ${\mathrm{C}}_{10}^{\ensuremath{-}}$ system is, to our knowledge, novel.