Femtosecond Spectroscopy of Heterogeneous Electron Transfer:  Extraction of Excited-State Population Dynamics from Pump−Probe Signals

Numerical calculations of pump−probe signals corresponding to excited-state absorption of the molecular state are presented. The molecular excited-state decays due to ultrafast electron injection into a continuum of electronic states (semiconductor levels) and the model calculations take into account the consequent molecular reorganization. A time-dependent Schrödinger wave equation approach is utilized to model the pump−probe dynamics. The continuum of semiconductor states, namely, its conduction-band levels, is described by an expansion in terms of orthogonal polynomials. It is shown that excited-state dynamics, including information on the modulation of population transfer due to vibrational coherences, can be unambiguously deduced from the pump−probe signals.