AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
A New Frontier of Ion Mobility Calculations; Coupling Molecular Dynamics to Kinetic Theory of Gases
CARLOS LARRIBA-ANDALUZ, IUPUI
Abstract Number: 423 Working Group: Aerosol Physics
Abstract Ion Mobility Spectrometry separation is obtained through the different ways charged molecular structures react to being drifted through a medium by means of an electrical field. This reaction is invariably attached to the inference of the collision cross section (CCS,Omega), which in most instances is the value used to obtain mobility diameters for non globular particles. Due to the complexity of the CCS, -which depends strongly on the gas used, temperature, scattering and vibrations of molecular atoms -numerical methods often make use of experimental parameters to obtain simplified models that are in general not accurate for all conditions. The accommodation coefficient often used in the Stokes Millikan approximation is one of such parameters. Here we try to couple Molecular Dynamics to our homemade IMoS software to numerically define some of these parameters. IMoS software mimics the interactions between an all-atom structure and a gas environment. The gas environment is calculated as an undisturbed real gas where densities, concentrations and kinetic velocities, i.e. gas temperature, are taken into consideration. Fluxes of gas molecules then enter the domain of calculation and interact with the traveling molecule exchanging momentum and energy with it. Until now the atoms were kept fixed and a set of parameters, either an accommodation coefficient or gas dependent Lennard-Jones constants, were obtained experimentally. In this work we obtain positions and velocities of the atoms from a Molecular Dynamics (MD) forcefield previously implemented and are used in IMoS to study reemissions. Preliminary Data shows that reemission depends strongly on the interaction between atoms and gas molecules. For Diatomic Nitrogen; reemission direction and velocities depend on the masses and velocities of the colliding atoms and trajectories differ from specular elastic to a more effectively diffuse condition.