The excitation of molecules by strong pulses can both induce photoexcitation and photoionization.  It is therefore crucial to develop methodologies that include both processes for the pump and for the probe steps to compute the dynamics. For the pump step, it is important to assess how much the dynamics of the interaction with the photoionization continua affects the electronic coherences that are built in the states of the neutral. Conversely, if the pump aims at building a superposition of electronic states of the cation, interactions with the neutral states during the pulse can modify the phase relations of the coherences of the cationic states. The same processes can also take place and exploited during the probe pulse. The simulation of such pump probe process over delays of several tens of femtoseconds requires quantum dynamics to fully account for nuclei motion during the pump, the time delay and the probe steps, in particular when the pulses are not ultrashort.<br/>We will report on the computation of coupled electronic-nuclear dynamics in the LiH and HCN molecules on several excited electronic states and including multiphoton ionization. We compute the dynamics by numerically integrating the nuclear time-dependent Schrödinger equation on a spatial grid and on several potential energy surfaces. We include the photoionization process using the partitioning method. The ionized states wave function is represented as an antisymmetrized product of the electronic states of the cation and of the state of the photoelectron. The wave function of the photoelectron is represented by a set of orthogonalized plane waves. The coupling between the wave function of the neutral and the wave function of the cation is computed at each grid point in nuclear coordinates as the transition dipole between the photoelectron wave function and the Dyson orbital that is defined as the overlap between the electronic state of the neutral and the electronic state of the cation. This method allows us computing the dynamics of LiH and HCN upon excitation by strong IR and UV femtosecond pulses. Depending on the pulse parameters, the dissociation of the LiH molecule yields a lithium atom in different electronic states. The dynamics of HCN in its excited states is more complex because of numerous conical intersections, and can lead to photo-isomerization or to photo-dissociation.

Partitionning method applied to the computation of ultrafast photoionization dynamics in small molecules induced by strong pulses

256th National Meeting (2018)

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