Modelling of transport properties of molecular ions of helium in air

Abstract

This thesis is focused on modeling of the transport properties of helium-based cold plasma in the interaction with nitrogen in the atmosphere. The main focus of this thesis is on thorough description of molecular interactions. The obtained results are further passed into molecular dynamics simulations and mesoscopic models of transport properties. The interactions are obtained via ab initio approach, utilizing Multi-Configurational Self-Consistent Field and Multi-Reference Configuration Interaction methods together with Numerov method for solving Schroedinger equation when computing vibrational-rotational excitations. Molecular dynamics is being performed in a hybrid quantum-classical approach, as nuclei are being treated classically and electrons in a quantum manner. Furthermore, not only ab initio methods on-the-fly, but also Artificial Neural Networks are involved in the dynamics simulations to reduce necessary runtime for the most expensive parts. Transport properties of the collision complexes are modelled using Monte Carlo. In this thesis, a thorough analysis of the molecular interactions for the ground and the first excited states of N2+ and N2+/He is given, with respect to different basis sets, orbital spaces and methods. The behavior is evaluated not only for the values of potential energy, but also for different rotational-vibrational excitations of N2+ and the preliminary results are also provided for the higher excited states up to 11th one and the 7th one in the case of N2+ and N2+/He, respectively. Both reactive and non-reactive cross-sections were obtained from molecular dynamics simulations and compared subsequently with the pseudo-experimental data obtained from mobility measurements. In this context, also the effect of the N2+ horizontal alignment on the resulting cross-sections was analyzed in detail. Finally, the mesoscopic modeling part was focused on obtaining N2+ mobility, in He gas, the characteristic energies of both longitudinal and transversal diffusion and the rate constant of N2+ diffusion induced by collision with He. That said, while the topic is not exhausted in any way, these theoretical findings are already useful for further experimental research, helping with "tuning" cold plasma for specific applications.