Abstract

In this work, various methods of computational chemistry have been applied to study the structure, photochemistry and dynamics of small anionic clusters in order to obtain some insight into the fundamental nature of molecule-molecule and electron molecule interactions. The main theme of this Thesis evolves around charge-transfer-to-solvent (CTTS) excited states of small halide-polar molecule clusters and concomitant phenomena, with specific attention to iodide-acetonitrile clusters I - (CH 3 CN) n . The structure of ground-state halide-acetonitrile complexes is determined by a competition between ion-dipole interactions and hydrogen bonding. The latter is dominant for complexes formed by all halide ions, except for the binary iodide acetonitrile complex I - (CH 3 CN), which is stabilized by only ion-dipole interactions. On the other hand, in the excited or ionized iodide complexes and clusters, the non-uniform electron density distribution around the neutral iodine atom due to the unpaired electron and spin-orbit coupling effects plays a very important role in interactions of the iodine atom with molecules or ions. The CTTS excitation of iodide-solvent clusters leads to the transfer of an electron from iodide to a diffuse dipole-bound orbital. The calculated excitation energies for the iodide-acetonitrile complex, as well as the vertical detachment energies of the excited electron have been found to be in a good agreement with available experimental data. For the first time, the relaxation dynamics of CTTS excited states in clusters has been studied by means of first-principles excited-state molecular dynamics simulations for paradigm iodide-acetonitrile I - (CH 3 CN) and iodide-water I - (H 2 O) 3 clusters. Whereas the departure of a neutral iodine atom can lead to stabilization of the excited electron, in agreement with state-of-the-art femtosecond spectroscopy experimental data, the solvent dynamics should not be neglected when interpreting experimental results. The photoexcitation and subsequent relaxation of I - (CH 3 CN) n clusters can lead to formation of acetonitrile cluster anions, which are characterized by the binding of the excess electron in a dipole-bound orbital outside of acetonitrile molecules, as shown for the prototype acetonitrile dimer anion. At the same time, in solution or relatively large clusters, two acetonitrile molecules can dimerize, forming a weak covalent carbon-carbon bond and allowing for delocalization and binding of the excess electron in their valence orbitals