Charge and proton dynamics in molecules and free clusters : from atomic to nanometer scale

Sammanfattning: The origin of properties in complex systems can often be traced to mechanisms involving charge and energy transfer in only a few embedded molecules. The detailed study of the time evolution of these mechanisms in their original environment is a challenging task. In this thesis we develop experimental tools and methods to enable the study of charge and energy transfer. A new ion and electron momentum imaging spectrometer, along with advanced data treatment methods has been succesfully designed, built and tested. The developed spectrometer is optimized for the measurement of the ion and electron momentum correlation that results from the fragmentation of complex systems, from molecules to molecular clusters.We have conducted photodissociation studies on such complex systems, using the newly developed experimental tools.The use of modern X-ray sources allows to localize the initial energy and charge to sites and/or elements in the system, from where the transfer is initiated.The energy and charge transfer is investigated in molecules by the local (multi-)photon absorption at a controlled site. Among other studies, we investigate the origin of the site-dependence of the fragmentation, be it the population of electronic excited states, conformational isomerization, fast hydrogen evaporation and migration, or secondary breakup. The influence of these processes on the fragmentation are investigated in two ways: through the C1s ionization of chemically distinct carbon sites (ethyl trifluoroacetate), and through the C1s excitation of a model system for conjugated (π) hydrocarbons (1,3 trans butadiene).The migration of charge and transfer of energy in embedded molecular systems is studied by the use of molecular clusters as model systems. The photo-induced energy and charge transport can be facilitated by intermolecular electronic decay, hydrogen migration, proton transfer, the Grotthus mechanism and nuclear rearrangement. The role of these processes in the stabilization and fragmentation of clusters is investigated in clusters of molecules containing N-H and O-H groups that form hydrogen bonds. Among other findings, we conclude that water is an effective stabilizer in multiply-charged hydrated ammonia clusters, which can play an important role in the nucleation process and photochemistry in atmospheric nanoparticles.