Simulation studies of simple gas desorption and development and spectroscopic studies of charge-scaled ion models.

摘要

This thesis focuses on two primary areas: charged solutes in water, and simple gas desorption from water and aqueous solutions. The former area directly relates to the Hofmeister series, an important topic not only for studies of salt solutions but also for understanding and predicting the behavior of proteins and other biomolecules in aqueous solutions. This thesis presents a new charge-scaling method for non-polarizable simulations of ionic solutions that offers unprecedented agreement with ion-concentration-dependent water diffusion trends. This model is computationally cheap, easy to implement, and shows agreement with experiment for several structural and dynamical properties, on par with some of the leading non-polarizable models.;The aforementioned model is used to study the terahertz spectra of alkali chloride solutions. These spectra are shown to exhibit a Hofmeister-like series in the water contribution to the spectra which has not been seen in studies that focused on only the ion contributions. Of particular importance is the fact that this Hofmeister effect shows strong dependence on the identity of the cation, whereas many other Hofmeister effects are only strongly influenced by the anion.;For gas desorption, we focus on understanding what causes non-Maxwellian evaporation and determining whether Maxwellian evaporation is actually fundamental to solute evaporation from liquid solvents. This is accomplished first by studying the trends in the dependence of the desorption energy on both the solute-solvent interaction energy and solute mass. The decomposition of the desorption energy into components corresponding to the velocity normal and tangential to the average surface is shown to be vitally important in understanding the underlying data. These trends are interpreted in terms of the potential of mean force (PMF) and the effectiveness and frequency of collisions during the evaporation process. The correlation of desorption energy with the PMF is shown to also hold as the solution temperature and composition are altered. In particular, the introduction of salts can greatly increase the solvation free energy and thus create very non-Maxwellian desorption.