Multiquantum vibrational excitation of NO scattered from Au(111): quantitative comparison of benchmark data to Ab initio theories of nonadiabatic molecule-surface interactions.

Measurements of absolute probabilities are reported for the vibrational excitation of NO(v=0→1,2) molecules scattered from a Au(111) surface. These measurements were quantitatively compared to calculations based on ab initio theoretical approaches to electronically nonadiabatic molecule–surface interactions. Good agreement was found between theory and experiment (see picture; Ts=surface temperature, P=excitation probability, and E=incidence energy of translation)

Steric Hindrance of NH3 Diffusion on Pt(111) by Co-Adsorbed O-Atoms

A detailed velocity-resolved kinetics study of NH3 thermal desorption rates from p(2 × 2) O/Pt(111) is presented. We find a large reduction in the NH3 desorption rate due to adsorption of O-atoms on Pt(111). A physical model describing the interactions between adsorbed NH3 and O-atoms explains these observations. By fitting the model to the derived desorption rate constants, we find an NH3 stabilization on p(2 × 2) O/Pt(111) of 0.147–0.014+0.023 eV compared to Pt(111) and a rotational barrier of 0.084–0.022+0.049 eV, which is not present on Pt(111). The model also quantitatively predicts the steric hindrance of NH3 diffusion on Pt(111) due to co-adsorbed O-atoms. The derived diffusion barrier of NH3 on p(2 × 2) O/Pt(111) is 1.10–0.13+0.22 eV, which is 0.39–0.14+0.22 eV higher than that on pristine Pt(111). We find that Perdew Burke Ernzerhof (PBE) and revised Perdew Burke Ernzerhof (RPBE) exchange–correlation functionals are unable to reproduce the experimentally observed NH3–O adsorbate–adsorbate interactions and NH3 binding energies at Pt(111) and p(2 × 2) O/Pt(111), which indicates the importance of dispersion interactions for both systems

Incidence energy dependent state-to-state time-of-flight measurements of NO(v=3) collisions with Au(111): the fate of incidence vibrational and translational energy.

We report measurements of translational energy distributions when scattering NO(v(i) = 3, J(i) = 1.5) from a Au(111) surface into vibrational states v(f) = 1, 2, 3 and rotational states up to J(f) = 32.5 for various incidence energies ranging from 0.11 eV to 0.98 eV. We observed that the vibration-to-translation as well as the translation-to-rotation coupling depend on translational incidence energy, E-I. The vibration-to-translation coupling, i.e. the additional recoil energy observed for vibrationally inelastic (v = 3 -> 2, 1) scattering, is seen to increase with increasing E-I. The final translational energy decreases approximately linearly with increasing rotational excitation. At incidence energies E-I > 0.5 eV, the slopes of these dependencies are constant and identical for the three vibrational channels. At lower incidence energies, the slopes gradually approach zero for the vibrationally elastic channel while they exhibit more abrupt transitions for the vibrationally inelastic channels. We discuss possible mechanisms for both effects within the context of nonadiabatic electron-hole pair mediated energy transfer and orientation effects

Vibrational excitation and relaxation of NO molecules scattered from a Au(111) surface

We present results of recent and ongoing experiments on molecular-beam surface scattering of NO molecules from a Au(lll) surface. Vibrational excitation of NO(ν=0) into ν=l,2 was studied in great detail over a wide range of incidence energies (0.10-1.05 eV) and surface temperatures (300-1100 K). We find behavior characteristic of electronically nonadiabatic coupling of molecular vibration to electron-hole pair excitation in the gold crystal. A state-to-state kinetic model shows that for ν=2 excitation both the sequential (0→1→2) and direct (0→2) excitation pathways are important. The absolute excitation probabilities are also compared to the results of a first principles independent-electron surface hopping calculation, and good agreement is obtained. In addition to ν=l,2 excitation, we present the first evidence for second-overtone ν=3 vibrational excitation. Preliminary data for vibrational relaxation of laser-prepared NO(ν=3) show strong relaxation; the intrinsic coupling strengths are consistent with those obtained from vibrational excitation. Measurements of the translational inelasticity of NO(ν=3) show that the molecules lose a large fraction of translational energy in the collision. The translation-vibration coupling is significant but may depend on incidence energy, and a clear anticorrelation is observed between the final translational and rotational energies

The importance of accurate adiabatic interaction potentials for the correct description of electronically nonadiabatic vibrational energy transfer: A combined experimental and theoretical study of NO(v=3) collisions with a Au(111) surface.

We present a combined experimental and theoretical study of NO(v = 3 -> 3, 2, 1) scattering from a Au(111) surface at incidence translational energies ranging from 0.1 to 1.2 eV. Experimentally, molecular beam-surface scattering is combined with vibrational overtone pumping and quantum-state selective detection of the recoiling molecules. Theoretically, we employ a recently developed first-principles approach, which employs an Independent Electron Surface Hopping (IESH) algorithm to model the nonadiabatic dynamics on a Newns-Anderson Hamiltonian derived from density functional theory. This approach has been successful when compared to previously reported NO/Au scattering data. The experiments presented here show that vibrational relaxation probabilities increase with incidence energy of translation. The theoretical simulations incorrectly predict high relaxation probabilities at low incidence translational energy. We show that this behavior originates from trajectories exhibiting multiple bounces at the surface, associated with deeper penetration and favored (N-down) molecular orientation, resulting in a higher average number of electronic hops and thus stronger vibrational relaxation. The experimentally observed narrow angular distributions suggest that mainly single-bounce collisions are important. Restricting the simulations by selecting only single-bounce trajectories improves agreement with experiment. The multiple bounce artifacts discovered in this work are also present in simulations employing electronic friction and even for electronically adiabatic simulations, meaning they are not a direct result of the IESH algorithm. This work demonstrates how even subtle errors in the adiabatic interaction potential, especially those that influence the interaction time of the molecule with the surface, can lead to an incorrect description of electronically nonadiabatic vibrational energy transfer in molecule-surface collisions