Efficient Vibrational Energy Redistribution between Stretching Modes: State-to-State Quantum Scattering of H_{2}O from Cu(111).

Abstract

State-to-state scattering dynamics of H_{2}O from Cu(111) has been studied by a fully coupled quantum mechanical model which explicitly accounts for the most important molecular degrees of freedom, based on a first-principles determined potential energy surface. When H_{2}O in its antisymmetric O-H stretching vibration (ν_{3}) collides with the surface, we find that the intramolecular vibrational energy redistribution (IVR) is predominant from ν_{3} to the symmetric stretching mode (ν_{1}), while rather inefficient to the bending mode (ν_{2}). This mode-specific IVR results from the strong couplings between stretching modes, which equally dispose the initial energy in ν_{3} into local stretching modes differing by a phase factor. Given the number of stretching modes in H_{2}O and CH_{4}, this mechanism naturally explains why the product ν_{1}/ν_{3} ratio calculated here is ∼3 times over that recently measured for CH_{4} scattering on Ni(111), suggesting that the nonstatistical IVR is more general than expected in polyatomic molecules.