Molecular dynamics simulations in bulk liquids and at liquid surfaces

The electronic spectra and the photodissociation on the excited state as well as vibrational relaxation on the ground state of OClO in the bulk and at the liquid/vapor interface of water, acetonitrile and ethanol are computed using classical molecular dynamics computer simulations. The photodissociation at the interface of all three liquids gives rise to nearly 100% cage escape compared to substantial geminate recombination in the bulk. This rise in the cage escape percentage is attributed to the reduced friction and to slower vibrational relaxation of OClO at the interface as well the ability for the photo fragments to desorb from the interface.; The vibrational relaxation of OCl and OCl− is studied by molecular dynamics computer simulations. Both equilibrium calculations of the vibrational friction and non-equilibrium simulation of the energy relaxation is used. The relaxation of the ionic solute is much faster than that of the non-ionic solute in both solvents. The relaxation is slowed down considerably when the non-ionic solute is transferred from the bulk to the interface, but no such surface effect is found in the case of the ionic solute. The ionic solute is able to keep its first solvation shell intact upon transfer to the interface and that the main contribution to the friction is due to the Lennard-Jones part of the intermolecular potential.; A potential energy model for the interactions between HCl and glycerol, based on the Empirical Valence Bond (EVB) approach, is developed and used to investigate by the early events following the collision of an HCl molecule with the glycerol surface. The calculated trapping probability at 10kJ/mol and 90kJ/mol collision energies and the fractional energy loss of scattered HCl molecules agree well with experiments. The potential of mean force for HCl in the bulk and at the glycerol surface exhibits a low barrier to the formation of the contact ion pair, suggesting the possibility of proton exchange at the interface. Trapped HCl molecules undergo rapid relaxation and solvation and begin to form contact ion pairs on the picosecond timescale, in agreement with the equilibrium potential of mean force calculations.