A framework for the theoretical description of two-pulse time-resolved ionization spectroscopy of ultrafast excited-state dynamics of polyatomic molecules is developed. The radiation–matter interaction as well as intramolecular couplings in the excited-state manifold are treated nonperturbatively by solving the time-dependent Schrödinger equation. The numerical solution is based on a discretization of the ionization continua which becomes particularly efficient for ultrashort laser pulses. With this method converged computations of ionization signals become possible even for complex molecular systems. Computer simulations are performed for a model system representing three-dimensional non-Born–Oppenheimer excited-state dynamics on conically intersecting potential-energy surfaces (the S1 and S2 surfaces of pyrazine). The dependence of the observable time-resolved ionization signals (total ion yield as well as photoelectron spectrum) on the properties of the laser pulses (carrier frequency and pulse duration) is explored. It is demonstrated that ultrafast electronic decay processes as well as coherent vibrational motion in excited states can be monitored by pump–probe ionization with suitable pulses. The dependence of the time-resolved ionization signals on properties of the cation (ionization potentials and potential-energy surfaces) is also discussed.

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Transient absorption experiments with probing in the blue part of the spectrum (440−500 nm) are performed for the electron-transfer system oxazine 1 in N,N-dimethylaniline. The experiments with high time resolution of better than 20 fs show pronounced modulations due to high-frequency wave packet motion (600 cm -1) in the excited electronic state of the oxazine 1 molecule before electron transfer. Additionally, modulations due to wave packet motion in the product state of oxazine 1 after complete charge separation are observed. The absorption transients related to the electron transfer from N,N-dimethylaniline to oxazine 1 are clearly nonmonoexponential with time constants of 30 and 80 fs. This behavior points to a strong adiabaticity of the electron-transfer reaction with a high relevance of nuclear motions.

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