Inelastic scattering of formaldehyde on Au(111) surface.

Inelastic scattering between gas molecules and surfaces is a fundamental process that has been investigated extensively. In recent gas-surface scattering experiments [Phys. Chem. Chem. Phys. 19, 19904 (2017)] on formaldehyde scattering off the gold surface, the scattered formaldehyde molecules had a high propensity to excite twirling motion about the C-O bond. In the work presented here, we used classical dynamics simulations to understand energy transfer in formaldehyde-surface collisions and to probe the mechanism of interconversion of translational energy to rotational energy. The simulations reveal an increase in the rotational energy distribution with an increase in collision energies and a preferential rotational excitation about the C-O bond consistent with the experiments. The high propensity to excite the twirling motion was found to arise from a steering motion about the C-O bond during the scattering process governed by the minimum energy path.