Non-adiabatic and time-resolved photoelectron spectroscopy for molecular systems

Journal Of Chemical Theory And Computation 10, 1665 - 1676 (2014)

Non-adiabatic and time-resolved photoelectron spectroscopy for molecular systems

J. Flick, H. Appel, A. Rubio

We quantify for a vibronic model system of Trans-Polyacetylene the non-adiabatic contributions to the vibronic sidebands of equilibrium and explicitly time-resolved nonequilibrium photoelectron spectra. Using exact diagonalization and by directly evaluating sum-over-states expressions for the linear-response photocurrent, we show that spurious peaks appear within the Born-Oppenheimer approximation of the related vibronic spectral function, which are not present in the exact spec- tral function of the system. The effect can be traced back to the factorized nature of the Born- Oppenheimer initial and final photoemission states and also persists when either only initial, or final states are replaced by correlated vibronic states. Only when correlated initial and final vibronic states are taken into account the spurious spectral weights are suppressed. In the nonequilibrium case, we illustrate for an initial Franck-Condon excitation and an explicit pump pulse excitation how the vibronic wavepacket motion of the system can be traced in the time-resolved photoelectron spectra as function of the pump-probe delay.

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