Reduced and full system-bath quantum dynamics of IR-driven adsorbate vibrations

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Adsorbate vibrations, excited by infrared (IR) light, play a role in many fields of chemistry and physics. Examples refer to spectroscopy, mode-selective chemistry, information technology, or energy transfer and storage at interfaces. As "open quantum systems", vibrations at surfaces are also of considerable fundamental interest, notably in the context of so-called "non-Markovian" behaviour and the preservation of coherences in molecular ensembles over long time periods. In the current project, the dynamics of elementary processes connected to the excitation and subsequent, relaxation of vibrations of atoms or molecules at semiconductor or insulator surfaces are studied theoretically with the help of quantum dynamical methods. Based on our work of the first funding period, the following aims will be addressed along these lines: For the example of hydrogen and deuterium adsorbed on a reconstructed silicon surface, (1) a systematic test of "reduced", open-system density matrix theory shall be performed in comparison to an "exact" treatment of system-bath dynamics using a time-dependent Schrödinger equation; (2) model Hamiltonians developed thus far shall be extended and efficient, numerical wavefunction-based methods shall be applied to treat IR excitation and relaxation caused by vibration-phonon coupling; (3) the interplay between IR excitation and relaxation shall be studied, notably towards the goal of mode-selective excitation in a dissipative environment. (4) For a second model system, carbon monoxide on a NaCl(100) surface, coarse grained density matrix models shall be developed to describe IR excitation and subsequent vibrational energy transfer in ensembles of adsorbed molecules. Here in particular, the phenomenon of "energy pooling" is of interest, for which current experiments show the occurrence of vibrationally very highly excited CO molecules.