Model studies on femtosecond time-resolved ionization spectroscopy of excited-state vibrational dynamics and vibronic coupling

The time-resolved detection of excited-state vibrational motion and vibronic coupling with femtosecond pump-probe ionization spectroscopy is analysed within the framework of lowest-order perturbation theory with respect to the radiation-matter interaction. It is shown for a simple model of shifted harmonic oscillators in the Condon approximation that coherent wave packet motion in the excited electronic state is reflected in the ion-yield signal when laser pulses of suitable duration are employed (neither too short nor too long). It is furthermore shown that the pronounced oscillatory electronic population dynamics of adiabatic electronic states induced by vibronic coupling can be monitored almost perfectly by pump-probe ionization with suitable pulses. In both cases we analyze the conditions (pulse durations and laser frequencies) under which the phenomena manifest themselves in the time-resolved ion-yield signal.