Collision Dynamics and Solvation of Water Molecules in a Liquid Methanol Film

Environmental molecular beam experiments are used to examine water interactions with liquid methanol films at temperatures from 170 K to 190 K. We find that water molecules with 0.32 eV incident kinetic energy are efficiently trapped by the liquid methanol. The scattering process is characterized by an efficient loss of energy to surface modes with a minor component of the incident beam that is inelastically scattered. Thermal desorption of water molecules has a well characterized Arrhenius form with an activation energy of 0.47{\pm}0.11 eV and pre-exponential factor of 4.6 {\times} 10^(15{\pm}3) s^(-1). We also observe a temperature dependent incorporation of incident water into the methanol layer. The implication for fundamental studies and environmental applications is that even an alcohol as simple as methanol can exhibit complex and temperature dependent surfactant behavior.Comment: 8 pages, 5 figure

Theoretical Study of the Dynamics of Collisions Between HCl and ω-Hydroxylated Alkanethiol Self-Assembled Monolayers

We present a classical-trajectory study of collisions of HCl with hydroxylated alkanethiol self-assembled monolayers. The potential-energy surface used in the trajectory propagation is a combination of the standard OPLS force field to describe the surface and an analytical potential for the gas/surface interaction developed in this work. The gas/surface potential has been derived based on high-quality electronic-structure calculations of model HCl-alcohol systems in the gas phase and includes a flexible Buckingham term and a Coulombic term. The results of the trajectories calculations are in good agreement with recent molecular-beam experiments on the same system, thereby lending support to the accuracy of the calculations. The collision dynamics differ vastly from prior scattering studies involving rare gases and CO, primarily because the gas/surface attraction governed by hydrogen bonding dramatically increases the ability of the gas molecules to trap on the surface for extended times. The properties of the desorbing HCl molecules are largely insensitive to the initial collision energy and are only mildly affected by the incident angle. An analysis of the reaction mechanism reveals the distinct dynamics of trajectories that either recoil from the surface directly or undergo multiple collisions with the surface and result in thermalization. © 2011 American Chemical Society