Effect of incident angle on the inelastic scattering of formaldehyde from an Au(111) surface.

The inelastic scattering of formaldehyde from an Au(111) surface was investigated using classical trajectory simulations at incident angles θi = 15°, 30°, 45°, and 60° with respect to the surface and collision energies Ei = 0.33, 0.39, 0.47, 0.88, and 1.21 eV. The simulations show a preferential excitation of cartwheeling rotational motion of formaldehyde upon collision with the gold surface for all incident angles and collision energies studied. This behavior contrasts with earlier reports for normal incidence (θi = 0°) at the same collision energies, where twirling rotational motion was found to be preferentially excited. The scattering process is non-random and leads to a skewed angular distribution, indicating partial retention of memory of the projectile's incident conditions. The average scattering angle increases with increasing incident angle for all collision energies. The translational energy loss during the collision is compensated by rotational energy gain, exhibiting a linear anti-correlation.