Femtochemistry, that is, chemistry at the femtosecond time-scale was one of the great discoveries of the end of last century and has answered many of the questions concerning the very microscopic nature of chemical reactions. It was then possible to observe the motion of nuclei in molecules with unprecedented time resolution.
Bimolecular reactions, i.e. those arising from the encounter between two molecules, have received little attention in this field, in particular because it is hard to control experimentally the relative orientations and impact parameters of the reactants.
The use of weakly bound complexes, i.e. aggregates of two molecules held together via mutual weak interaction, offers a solution to this problem. By forming such a complex, the reactants are initially placed at well-defined relative positions. A short laser pulse is then shined on the complex to initiate the reaction between the two. While this method has been applied in a few situations in the past, theoretical investigations supporting the interpretation of the results are lacking.
In this thesis, we show with quantum mechanical simulations how the weakly bound complex (HCl)…(HOD) can be used to study the prototypical bimolecular collision between H and HOD. It is shown that the selectivity of the resulting reaction is a result of the well-defined initial position of the reactants given by the geometry of the complex. In addition, it is shown that this selectivity can be tuned by vibrational pre-excitation of the HOD moiety.
Additionally, in order to be able to characterize weakly bound complexes, we have constructed a new matrix isolation setup coupled to an infrared spectrometer. This has been applied for the study of the (HCl)…(H2O) complex and its spectral signature in the mid-infrared region is revealed.