Modeling the Molecular Physics in Dynamic Plume Simulations of a Single-emitter Electrospray Thruster

Understanding the behavior of complex molecular ion beams is essential for advancing a wide range of plasma and ion-based technologies, including electrospray thrusters. In such systems, the plume consists of solvated ions and neutral species that undergo dissociation and intermolecular collisions, resulting in a dynamically evolving distribution of chemical species with a variety of charge-to-mass ratios. The proposed presentation would integrate two complementary studies that capture the molecular-scale physics influencing plume dynamics from a single-emitter electrospray thruster operating with 1-ethyl-3-methylimidazolium tetrafluoroborate (C₆H₁₁N₂-BF₄) ionic liquid. The first study focuses on collisional interactions between molecules with different charge-to-mass ratios, such as [C₆H₁₁N₂]⁺ monomers and C₆H₁₁N₂-BF₄ neutrals. Using reactive molecular dynamics (MD), different types of collisional interactions are quantified in terms of cross-sections, enabling direct incorporation into larger-scale n-body simulations that model an entire plume from a single emitter. The second study develops a thermal fragmentation model for the [C₆H₁₁N₂]⁺ monomer using reactive molecular dynamics and transition state theory (TST), revealing how molecular integrity depends on ion temperature and the local electric field. N-body simulations under realistic electric field gradients predict negligible fragmentation in the acceleration region at nominal temperatures (∼330 K), but show increased fragmentation at elevated temperatures (∼550 K), providing a quantitative basis for incorporating thermal stability of monomers into n-body simulations of plume evolution. These investigations provide a multiscale framework linking molecular physics to macroscopic plume properties. The unified approach enables predictive capability for modeling ion transport and composition in complex molecular beams.