Inhaltszusammenfassung

The formation of diatomic molecules or radicals in the cooling phase of a laser-induced plasma is mainly determined by thermodynamical parameters as the local plasma temperature, pressure and particle density. We adapted the well-known method ReaxFF to simulate the generation of molecular bonds in our time-resolving LIBS experiments. Instead of standard quantum mechanical or continuous simulation methods, ReaxFF uses a hybrid form based on the calculation of the bond order. The main advan...The formation of diatomic molecules or radicals in the cooling phase of a laser-induced plasma is mainly determined by thermodynamical parameters as the local plasma temperature, pressure and particle density. We adapted the well-known method ReaxFF to simulate the generation of molecular bonds in our time-resolving LIBS experiments. Instead of standard quantum mechanical or continuous simulation methods, ReaxFF uses a hybrid form based on the calculation of the bond order. The main advantage is the short computation time of molecular bonds compared to standard approaches. For several elements the specific parameters of the atomic force-fields are provided by Adri van Duin from Caltech University. This allows the simulation of molecular formation at a fixed thermodynamic equilibrium as well as ramp simulations to reveal temperature dependent molecular concentration profiles. Our molecular simulations allow to explain the observed molecular band emission, to investigate molecular interferences with other elements in the sample, and to determine the parameters of LIBS experiments in order to obtain high molecular band emission rates. As an application, we simulated the temporal behavior of molecular and radical species of CaO and CaCl to explain the observed molecular band emission of chloride-contaminated concrete. Quantitative LIBS measurements can help to determine the chloride content of buildings such as bridges or parking garages. Their stability is drastically reduced by the diffusion of chloride from de-icing salt into the concrete. Corrosion of the steel reinforcement occurs if the chloride contamination exceeds a certain level.» weiterlesen» einklappen

Autoren

Klassifikation

DFG Fachgebiet:
Optik, Quantenoptik und Physik der Atome, Moleküle und Plasmen

DDC Sachgruppe:
Physik