With the aid of molecular dynamics simulations, we study the structure and dynamics of different ionic liquid systems, with focus on hydrogen bond, ion pair and ion cage formation. To do so, we report radial distribution functions, their number integrals, and various time–correlation functions, from which we extract well-defined lifetimes by means of the reactive flux formalism. We explore the influence of polarizable force fields vs. non-polarizable ones with downscaled charges (±0.8) for the example of 1-butyl-3-methylimidazolium bromide. Furthermore, we use 1-butyl-3-methylimidazolium trifluoromethanesulfonate to investigate the impact of temperature and mixing with water as well as with the chloride ionic liquid. Smaller coordination numbers, larger distances, and tremendously accelerated dynamics are observed when the polarizable force field is applied. The same trends are found with increasing temperature. Adding water decreases the ion–ion coordination numbers whereas the water–ion and water–water coordination is enhanced. A domain analysis reveals that the nonpolar parts of the ions are dispersed and when more water is added the water clusters increase in size. The dynamics accelerate in general upon addition of water. In the ionic liquid mixture, the coordination number around the cation changes between the two anions, but the number integrals of the cation around the anions remain constant and the dynamics slow down with increasing content of the chloride ionic liquid.

Multiphase reactions of ozone with human skin oils impact indoor air quality by depleting ozone and forming semi-volatile organic compounds, which can be respiratory and skin irritants. Here we demonstrate the impact of clothing on indoor air composition and human exposure by integrating indoor chemistry modeling over a wide range of different spatial and temporal scales. Constrained by molecular dynamics simulations that provide key kinetic parameters, the kinetic model reproduces experimental measurements and predicts that squalene could persist in clothing for several hours to over a day depending on ozone concentrations. Soiled clothing protects skin from ozone exposure even with high concentrations, but can enhance concentrations of oxidation products to a ppb level depending on air exchange rates. Computational fluid dynamics simulations reveal that primary products have ~1.6–2.0 times higher concentrations in the breathing zone than in bulk room air, while secondary products are distributed more uniformly throughout a room.

We study the structure and dynamics of water subject to a range of static external electric fields, using molecular dynamics simulations. In particular, we monitor the changes in hydrogen bond kinetics, reorientation dynamics, and translational motions of water molecules. We find that water molecules translate and rotate slower in electric fields because the tendency to reinstate the aligned orientation reduces the probability of finding a new hydrogen bond partner and hence increases the probability of reforming already ruptured bonds. Furthermore, dipolar alignment of water molecules with the field results in structural and dynamic anisotropies even though the angularly averaged metrics indicate only minor structural changes. Through comparison of selected nonpolarizable and polarizable water models, we find that the electric field effects are stronger in polarizable water models, where field-enhanced dipole moments and thus more stable hydrogen bonds lead to slower switching of hydrogen bond partners and reduced translational mobility, compared to a nonpolarizable water model.

We present a first-principles calculation and mechanistic characterization of the ion product of liquid water (K _W ), based on Quantum Cluster Equilibrium (QCE) theory with a variety of ab initio and density functional methods. The QCE method is based on T-dependent Boltzmann weighting of different-sized clusters and consequently enables the observation of thermodynamically less favored and therefore low populated species such as hydronium and hydroxide ions in water. We find that common quantum chemical methods achieve semi-quantitative accuracy in predicting K _W and its T-dependence. Dominant ion-pair water clusters of the QCE equilibrium distribution are found to exhibit stable 2-coordinate buttress-type motifs, all with maximally Grotthus-ordered H-bond patterns that successfully prevent recombination of hydronium and hydroxide ions at 3-coordinate bridgehead sites. We employ standard quantum chemistry techniques to describe kinetic and mechanistic aspects of ion-pair formation, and we obtain NBO-based bonding indices to characterize other electronic, structural, spectroscopic, and reactive properties of cluster-mediated ionic dissociation.