INTERNAL-CONVERSION IN HIGHLY EXCITED BENZENE AND BENZENE DIMER - FEMTOSECOND TIME-RESOLVED PHOTOELECTRON-SPECTROSCOPY

Photoelectron spectra of benzene molecules and dimers excited to the S -2 electronic state by 140 fs laser pulses at a wavelength of 200 nm h ave been measured by combining the pump-probe technique with the coinc idence detection of ions and electrons. Their time dependence allows o ne to directly follow the evolution of internal conversion processes i n different electronic states on a fs time-scale. Analysis of the corr esponding electron energy distribution reveals large variations in the geometry of the different electronic states in both benzene and in it s dimer. (C) 1997 Published by Elsevier Science B.V.