A fully quantum theory of ultrafast chemical dynamics.

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In 1929 Dirac stated that: "The fundamental laws necessary for the mathematical treatment of a large part of physics and the whole of chemistry are thus completely known, and the difficulty lies only in the fact that application of these laws leads to equations that are too complex to be solved." We will show that recently developed methods of quantum dynamics can now overcome the difficulty noticed by Dirac. The fundamental outcome of the current project will be to show that the dynamics of a moderately complicated polyatomic molecule can now be described solely on the basis of quantum lows of motion albeit on a very short time scale of few hundred femtoseconds. Recently developed methods of Quantum Direct Dynamics which treat all electrons and nuclei of a molecule on a fully quantum level will be used to simulate the movements of molecules which follow the absorption of a UV photon. On the ultrafast time scale this motion always reveals a wealth of quantum phenomena such as electronically nonadiabatic processes (i.e. the changes in electronic states when electrons forming chemical bonds rearrange) and tunnelling. On the practical side the project will focus on 3 types of experiments. First, hydrogen photo- detachment from small heteroaromatic molecules studied in the gas phase will be simulated. In these experiments the initial excitation of a molecule by a photon initiates chemistry and causes the dissociation of hydrogen, which is later ionised with time delay of a few tens of femtoseconds and the "ion image" of the reaction is detected. This allows to obtain very detailed information about the dynamics of reaction by analysing the evolution of spatial and energy distribution of its products. Second, the new pump-probe experiments have been developed to study similar reactions in solution with femtosecond time resolution. These experiments provide time resolved spectral images of chemical reactions which allow to reconstruct the dynamics and to see their mechanisms. Third, new and unique experiments are becoming possible now with the construction of the new international Free Electron Laser X-ray facilities in Stanford and Hamburg. In the new time resolved X-ray diffraction experiment, an X-ray probe pulse is combined with femtosecond laser pulses in the visible and UV region, which initiate chemistry, and chemical dynamics is followed by measuring the changes in the X-ray diffraction images. The molecules studied in the above experiments often represent prototypes or building blocks of larger biologically important molecular species and their photodynamics often models the processes in living organisms, which occur under the influence of light. The proposed theory will explain the experiments and will help to unravel new mechanisms of the ultrafast chemistry. On the other hand the fully quantum theory will be benchmarked against experiment and it will be shown that the difficulty pointed out by Dirac can now be overcome.