Theoretical study of photoinduced reactions in ionic crystals mechanisms, energy dissipation and coherence effects

Recent advances in laser technology have allowed driving coherent microscopic dynamics of reactive species in some chemical reactions. This technique is called coherent control or quantum control. The possibility of coherent control in reactive centres in direct contact with ionic crystals was studied theoretically on the example reactions: (1) Desorption of hydrogen from a hydroxyl ion formed due to HCl adsorption at the MgO(001) surface and (2) dissociation of the Self-Trapped Exciton (STE) in alkali halides into a pair of point defects (F-H pair). The second takes place inside a crystal lattice. A complete self-contained theoretical study of the coherent control reaction (1) is presented, involving DFT calculations and classical and quantum dynamics simulations. Reaction schemes for (2) are studied using an empirical model for the STE in a generic alkali halide. To perform the tasks required by the aims of this project, a simple criterion for the spatial localisation of normal modes, a molecular dynamics initialisation scheme allowing dissipation dynamics at non-zero temperature and an extension of the optimal control method that greatly enhances its usability were developed. All of these techniques are applicable to a large class of theoretical problems. Comparative studies of phonon modes localised at surfaces and surface steps in three ionic crystals lead to the conclusion that the order of these crystals with increasing localisation of surface modes is CaF₂(111), MgO(001), KBr(001). For MgO and KBr, step modes were found that appear to be capable of funnelling vibrational energy to the step and transport it along the step. Vibrational modes localised at the corners of a large finite cube of MgO were identified that may play an important role in the dissipation from admolecule modes of the appropriate frequency. Reaction (1) is justified by the comparatively low localisation in MgO(001) in conjunction with a low anharmonicity, promising small dissipation from the admolecule. Density functional simulations ...