Scattering of water from graphite:: simulations and experiments

The scattering of water molecules from a graphite (0001) surface has been studied experimentally and using molecular dynamics simulations. Model potentials for the gas-solid interaction have been developed and tested by comparing experimental and simulated angular distributions for different translational energies (0.09-0.8 eV), incident angles (30-75 degrees) and surface temperatures (300-1200 K). Good agreement is found for both scattering intensities and angular resolved average velocities, supporting the main features of the model potentials. The importance of trapping at low incident: energy is discussed as well as the possibility of vibrational excitation at high collision energy. The latter phenomenon is investigated using purely classical trajectory calculations, a forced oscillator model and a wavepacket propagation scheme. The results indicate that meaningful estimates of the vibrational excitation can be obtained using classical simulations, supporting previously reported results on the CF3Br/graphite system [M.B. Nagard, N. Markovic, J.B.C, Pettersson, J. Chem. Phys. 109 (1998) 10350]. (C) 1999 Elsevier Science B.V. All rights reserved.