Ionization Pathway Interference in Photoionization Time Delays in Molecules.

The photoionization time-delay in linear conjugated molecules is computed using the Wigner scattering approach. We find that, in general, there are two additive contributions to the ionization time-delays. One originates from interferences between various ionization pathways that belong to different cationic eigenstates, while the other is due to time delays associated with each pathway and originates due to electron-electron correlations in the molecule. The former contribution scales up rapidly with the conjugation length, leading to larger time delays, as observed in recent experiments, while the latter is much less sensitive to the molecular conjugation.

Ionization Induced Time Delay in Hole Dynamics in Molecules.

Ionization time delay is a measure of the time of arrival of an electron from a bound molecular state to a free state. A similar time scale is associated with the hole dynamics in response to the ionization. We show that the ionization time delay and the time delay in hole dynamics are interdependent. Both time delays originate due to complex amplitudes of multiple ionization pathways, which lead to different cationic states. For sudden ionization (zero ionization time delay), the time delay for hole dynamics vanishes. We compute the ionization and hole dynamics time delays in glycine molecule and show how the photoionization process influences the hole dynamics and leads to nonzero hole-density flux as soon as the ionization takes place.

Photo-Ionization Time Delay in Linearly Extended π-Conjugated Molecular Systems.

We calculate the photo-ionization time delay for extended, linear, π-conjugated molecules. Ionization can be realized as scattering of an electron from bound to continuum states due to interaction with an ionizing radiation field. This allows us to use the Wigner method, whereby the rate of change in phase of the scattered electron wave packet with respect to the electron energy gives a measure of the ionization time delay. An analytical expression for ionization time delay is obtained using a model system that shows how interference between different ionization pathways leads to a finite time delay, even if there is a zero time delay corresponding to individual pathways. It is observed that the ionization time delay increases linearly as the size of the chain increases. We compute the ionization time delay also using computational chemistry and compare the results with those obtained from the model system. In qualitative agreement with the model calculation, we find that the ionization time delay increases linearly with increasing conjugation.

The Photoionization Time in π-Conjugated Molecular Systems.

The photoionization time of C2H4 is calculated as a model for π-conjugated molecular systems. Analytical results are obtained using the Wigner phase delay, which is compared with energy-streaking measurements. We find that, although the ionization time averaged over nuclear configurations compares well in the two measures, the dependence on the nuclear configuration is different. Interference between different ionization pathways depends significantly on the molecular geometry and the ionizing electron energy and may lead to qualitative changes in the ionization time.