Experimental and Theoretical Study of Multi-QuantumVibrational Excitation: NO(v= 0→1,2,3) inCollisions with Au(111).

Wemeasured absolute probabilities for vibrational excitation ofNO(v= 0) molecules in collisions with a Au(111)surface at an incidence energy of translation of 0.4 eV and surfacetemperatures between 300 and 1100 K. In addition to previously reportedexcitation to v= 1 and v= 2, weobserved excitation to v= 3. The excitation probabilitiesexhibit an Arrhenius dependence on surface temperature, indicatingthat the dominant excitation mechanism is nonadiabatic coupling toelectron–hole pairs. The experimental data are analyzed interms of a recently introduced kinetic model, which was extended toinclude four vibrational states. We describe a subpopulation decompositionof the kinetic model, which allows us to examine vibrational populationtransfer pathways. The analysis indicates that sequential pathways(v= 0 → 1 → 2 and v= 0 → 1 → 2 → 3) alone cannot adequately describeproduction of v= 2 or 3. In addition, we performedfirst-principles molecular dynamics calculations that incorporateelectronically nonadiabatic dynamics via an independent electron surfacehopping (IESH) algorithm, which requires as input an ab initio potentialenergy hypersurface (PES) and nonadiabatic coupling matrix elements,both obtained from density functional theory (DFT). While the IESH-basedsimulations reproduce the v= 1 data well, they slightlyunderestimate the excitation probabilities for v=2, and they significantly underestimate those for v= 3. Furthermore, this implementation of IESH appears to overestimatethe importance of sequential energy transfer pathways. We make severalsuggestions concerning ways to improve this IESH-based model. [ABSTRACT FROM AUTHOR]