Dynamics of water adsorption on Pt{110}-(1 X2): A molecular dynamicsstudy

摘要

Recent experimental studies of water adsorption on Pt{ 110}-(1 X 2) using supersonic molecularbeams [F. R. Laffir et al., J. Chem. Phys. 128, 114717 (2008)] have revealed that the translationalenergy dependence of the initial sticking probability is a stepwise function with a threshold energyof 5 kJ/mol. The initial sticking probability increases sixfold from 0.1 (at translational energiesless than 5 kJ/mol) to -0.64 (at translational energies greater than 10 kJ/mol). The aim of this workis to study the adsorption dynamics of water using classical molecular dynamics simulation in orderto assess what physical factors are responsible for the observed behavior of the initial stickingprobability. The simulations were performed using a purpose-designed code; water molecules weremodeled using the well-known TIP4P water model, whereas the water-platinum potential energyfunction was determined using the ab initio density functional theory calculations. We conclude thatthe main factor controlling the initial sticking probability is a relatively weak energy transferbetween the water molecule and the surface substrate during collision. This energy transfer isenhanced when the total energy of the water molecule increases. The assumption of an exponentialincrease of the probability of the energy transfer as a function of total energy of water moleculegives initial sticking probabilities very similar to those experimentally obtained. The same modelwas applied for the simulation of the coverage dependent sticking probability using a hybrid methodcomprising molecular dynamics and kinetic Monte Carlo approaches. We found a reasonableagreement between our results and the experimental data. The sticking probability as a function ofcoverage initially increases due to an increasing amount of the adsorbate island edges; it reaches amaximum and finally decreases as the islands merge together at high coverage. The saturationcoverage was determined to be 2.8 ML at surface temperature 165 K, where water forms a puckeredalmost regular lattice with each water molecule having four nearest neighbors. At the studiedtemperature we did not observe the existence of stable water multilayers on the surface which isconsistent with the experimental findings