A theoretical description of the motion of the nuclei on multiple electronic states of a diatomic molecule pumped by an intense laser field is discussed. We analyze the coherent dynamics of the wavepackets created on each electronic state during such an ultrafast excitation. Representation of the wavepackets on the grid of internuclear distances allows us to examine the non-local character of the nuclear motion. This is enabled by using a localized form of the momentum and kinetic energy operators within the finite difference approximation. It is a quantum mechanical description which yet introduces a Hamiltonian with coupling only to near neighboring points on the grid.<br/>A wave function is not quite analogous to a classical trajectory. This is particularly so when one aims to describe an excitation from an initial state. We typically choose a stationary initial state so that the change is due to the perturbation. Such an initial state is usually delocalized in the coordinates of the atoms. This is quite different from the initial conditions of a classical trajectory that initiates at a particular configuration. Analysis of the quantum mechanical equations of motion on the grid shows that the nuclear dynamics is driven by the coherences between the amplitudes of the adjacent points. Representing the initial wave packet dynamics by an ensemble of these classical trajectories is limited as each one moves independently of the other. Lost thereby is the effect of the non-locality (meaning coherence between amplitudes on adjacent grid points) of the momentum and kinetic operators on the propagation. Several computational examples of coherence effects in the attosecond coupled electron-nuclear dynamics in diatomic molecules are presented.

Coherence as a driving force for the nuclear motion during non-equilibrium electron dynamics

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.