Rotationally and vibrationally inelastic collisions of NH3 with Au(111): Experiment and theory

The authors measured angular, velocity, and quantumstate distributions for ammonia molecules scattered from a gold (111) single crystal for a number of surface temperatures and incident beam energies. To explain the experimental observations, the authors developed a classical trajectory code for scattering of a rigid nonlinear molecule from a rigid flat gold surface. The authors' classical trajectory calculations predict the propensity for tumbling vs spinning seen experimentally. The distribution of scattered molecules is markedly non-Boltzmann with low-K states preferentially populated. The authors extended their classical trajectory model to include the umbrella vibrational motion in NH3. The model predicts very efficient transfer of translational energy to the umbrella vibrational mode. The vibrational excitation is predicted to scale with the normal component of incident kinetic energy in agreement with the experimental observation