Vibration–rotational coupling of H2 molecules scattering from a Cu(1 1 1) surface

Vibration–rotational (V–R) correlations in the scattering of H2 molecules from Cu(1 1 1) surfaces have been investigated by jointly applying a quantum wavepacket model and a classical trajectory model. Two distinct phenomena have been understood on the same footing, which are vibrational excitation accompanied by rotational cooling (VEARC) and rotational excitation accompanied by vibrational de-excitation (REAVD). The former has been previously observed in experiments and can be attributed to rotation-to-vibrational (R→V) energy transfer, and REAVD is predicted by the present study and can be attributed to the reverse V→R transfer. It is shown that the canonical potential energy surfaces for a diatomic molecule interacting with a surface are generally able to facilitate efficient coupling between molecular rotation and vibration, which in turn leads to both R→V and V→R processes. The homonuclear symmetry of an H2 molecule, in combination with weak azimuthal dependence of atop surface sites where molecular vibrational excitation occurs preferentially, imposes important constraints on VEARC and REAVD processes.