Theoretical description of strongly coupled nuclear and electronic motion in ultrafast photoinduced molecular processes and their control

Chemical bond formation, cleavage or geometrical changes occur on the ultrafast time scale. Both in the gas phase and in the condensed phase the fast transformations are determined by an intricate interplay of the dynamics of the atomic nuclei and of the electrons moving with different speed. Real time observation of their motions during chemical changes requires light sources as developed and applied in A.1, C.1 and C.2 that span a time scale from femto- to attoseconds.
Beyond observation, coherent control of nuclear and electron motion is a major challenge on the way to light controlled molecular functionality. Modulated light fields in the femtosecond time domain control the nuclear motion and are realized in closed loop experiments. The recent accessibility of attosecond and fully field controlled pulses sparked the interest to directly control the much faster electrons.
We develop new theoretical tools for the description and interpretation of the novel experiments performed in the research areas C.1 and C.2. Our focus hereby is on a quantum dynamical description of electron and nuclear motion induced by waveform controlled and tunable few-fs light pulses. The central questions we want to answer are:

• What determines the speed of the chemical changes connecting individual quantum states in the reactants and products?
• What is the detailed underlying mechanism – its interplay between induced electric fields and molecular mobility - that steers the reaction on the fast time scales from atto- to picoseconds?
• To what extend can molecular reactions be controlled by laser light?
• Is there a way to attosecond chemistry?

New algorithms are developed for electron translocation, the simultaneous quantum dynamical description of nuclear and electronic motion and for the simulation of laser control experiments. We will balance our efforts between supporting current experiments and exploring theoretical frontiers. The systems under investigation range from selected diatomics to polyatomics.
For large systems, we focus on processes essential in ultrafast photoinitiated chemistry, like optical switches and precursors for electrophile S_N-reactions, and in biology like energy conversion systems. From electronic structure calculations and quantum dynamics simulation, we can provide an atomistic description of the reaction mechanism. Based on this knowledge realistic control strategies will be developed and optimal control theory will be used to design and predict shaped laser fields to control ultrafast photoreactions (C.2.5) in real time with the ultimate goal to generate functionality on the molecular scale. For the required optical processes, including non-resonant transitions, already available methods for the solution of the time-dependent Schrödinger equation or reduced density-matrix equations of motion will be further developed. Novel optimal control algorithms will be constantly adjusted to work out control scenarios for photochemical processes by optimizing light fields combined with solvents and substituents effects. With the help of multi objective optimization algorithms we will explore the limits of the efficiency of regenerative energy sources such as dye-sensitized solar cells (C.2.3).
For the small systems we study the possibility of feedback control (C.2.2) on single molecules stored in an ion crystal. Together with the experiments in C.2.7, we study the electron localization effects controlled by the carrier envelope phase (CEP) in strong few cycle pulses. We will extend the electron dynamic studies to chemical reactions like pericyclic reactions, which involve large electronic motions. The manipulation of the valence electron dynamics discloses new horizons for the control of ultrafast chemical reactions.