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This work presents systematic comparisons between classical molecular dynamics (cMD) and quantum dynamics (QD) simulations of 15-dimensional and 75-dimensional models in their description of H atom scattering from graphene. We use an experimentally validated full-dimensional neural network potential energy surface of a hydrogen atom interacting with a large cell of graphene containing 24 carbon atoms. For quantum dynamics simulations, we apply Monte Carlo canonical polyadic decomposition to transform the original potential energy surface (PES) into a sum of products form and use the multi-layer multi-configuration time-dependent Hartree method to simulate the quantum scattering of a hydrogen or deuterium atom with an initial kinetic energy of 1.96 or 0.96 eV and an incident angle of 0°, i.e., perpendicular to the graphene surface. The cMD and QD initial conditions have been carefully chosen in order to be as close as possible. Our results show little differences between cMD and QD simulations when the incident energy of the H atom is equal to 1.96 eV. However, a large difference in sticking probability is observed when the incident energy of the H atom is equal to 0.96 eV, indicating the predominance of quantum effects. To the best of our knowledge, our work provides the first benchmark of quantum against classical simulations for a system of this size with a realistic PES. Additionally, new projectors are implemented in the Heidelberg multi-configuration time-dependent Hartree package for the calculation of the atom scattering energy transfer distribution as a function of outgoing angles. [ABSTRACT FROM AUTHOR]

The Born–Oppenheimer approximation (BOA), which serves as the basis for our understanding of chemical bonding, reactivity and dynamics, is routinely violated for vibrationally inelastic scattering of molecules at metal surfaces. The title-field therefore represents a fascinating challenge to our conventional wisdom calling for new concepts that involve explicit electron dynamics occurring in concert with nuclear motion. Here, we review progress made in this field over the last decade, which has witnessed dramatic advances in experimental methods, thereby providing a much more extensive set of diverse observations than has ever before been available. We first review the experimental methods used in this field and then provide a systematic tour of the vast array of observations that are currently available. We show how these observations – taken together and without reference to computational simulations – lead us to a simple and intuitive picture of BOA failure in molecular dynamics at metal surfaces, one where electron transfer between the molecule and the metal plays a preeminent role. We also review recent progress made in the theory of electron transfer mediated BOA failure in molecule–surface interactions, describing the most important methods and their ability to reproduce experimental observation. Finally, we outline future directions for research and important unanswered questions. [ABSTRACT FROM AUTHOR]

This document is an erratum for an article titled "Quantum and classical molecular dynamics for H atom scattering from graphene" published in the Journal of Chemical Physics. The erratum states that Figure 12 in the original article was mixed with other results and provides the correct figure, which is now labeled as Figure 1. The figure shows the outgoing kinetic energy distribution for H atoms with different initial kinetic energies attacking different parts of the graphene structure. The authors of the original article are Lei Shi, Markus Schröder, Hans-Dieter Meyer, Daniel Peláez, Alec M. Wodtke, Kai Golibrzuch, Anna-Maria Schönemann, Alexander Kandratsenka, and Fabien Gatti. [Extracted from the article]

We investigated the translational incidence energy (E¡) and surface temperature (Ts) dependence of CO vibrational excitation upon scattering from a clean Au(111) surface. We report absolute v = 0 → 1 excitation probabilities for E¡ between 0.16 and 0.84 eV and Ts between 473 and 973 K. This is now only the second collision system where such comprehensive measurements are available - the first is NO on Au(111). For CO on Au(111), vibrational excitation occurs via direct inelastic scattering through electron hole pair mediated energy transfer - it is enhanced by incidence translation and the electronically non-adiabatic coupling is about 5 times weaker than in NO scattering from Au(111). Vibrational excitation via the trapping desorption channel dominates at E¡ = 0.16 eV and quickly disappears at higher E¡. [ABSTRACT FROM AUTHOR]

We report measurements of the incidence translational energy dependence of steric effects in collisions of NO(v = 3) molecules with a Au(111) surface using a recently developed technique to orient beams of vibrationally excited NO molecules at incidence energies of translation between 0.08 and 0.89 eV. Incidence orientation dependent vibrational state distributions of scattered molecules are detected by means of resonance enhanced multiphoton ionization spectroscopy. Molecules oriented with the N-end towards the surface exhibit a higher vibrational relaxation probability than those oriented with the O-end towards the surface. This strong orientation dependence arises from the orientation dependence of the underlying electron transfer reaction responsible for the vibrational relaxation. At reduced incidence translational energy, we observe a reduced steric effect. This reflects dynamical steering and re-orientation of the NO molecule upon its approach to the surface. [ABSTRACT FROM AUTHOR]

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 quantumstate 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. [ABSTRACT FROM AUTHOR]

We describe a method to obtain absolute vibrational excitation probabilities of molecules scattering from a surface based on measurements of the rotational state, scattering angle, and temporal distributions of the scattered molecules and apply this method to the vibrational excitation of NO scattering from Au(111). We report the absolute excitation probabilities to the v = 1 and v = 2 vibrational states, rotational excitation distributions, and final scattering angle distributions for a wide range of incidence energies and surface temperatures. In addition to demonstrating the methodology for obtaining absolute scattering probabilities, these results provide an excellent benchmark for theoretical calculations of molecule-surface scattering. [ABSTRACT FROM AUTHOR]

Translational motion is believedto be a spectator degree of freedomin electronically nonadiabatic vibrational energy transfer betweenmolecules and metal surfaces, but the experimental evidence availableto support this view is limited. In this work, we have experimentallydetermined the translational inelasticity in collisions of NO moleculeswith a single-crystal Au(111) surfacea system with strongelectronic nonadiabaticity. State-to-state molecular beam surfacescattering was combined with an IR-UV double resonance scheme to obtainhigh-resolution time-of-flight data. The measurements include vibrationallyelastic collisions (v= 3→3, 2→2) aswell as collisions where one or two quanta of molecular vibrationare excited (2→3, 2→4) or de-excited (2→1, 3→2,3→1). In addition, we have carried out comprehensive measurementsof the effects of rotational excitation on the translational energyof the scattered molecules. We find that under all conditions of thiswork, the NO molecules lose a large fraction (∼0.45) of theirincidence translational energy to the surface. Those molecules thatundergo vibrational excitation (relaxation) during the collision recoilslightly slower (faster) than vibrationally elastically scatteredmolecules. The amount of translational energy change depends on thesurface temperature. The translation-to-rotation coupling, which iswell-known for v= 0→0 collisions, is foundto be significantly weaker for vibrationally inelastic than elasticchannels. Our results clearly show that the spectator view of thetranslational motion in electronically nonadiabatic vibrational energytransfer between NO and Au(111) is only approximately correct. [ABSTRACT FROM AUTHOR]

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]

We report accurate time-resolved measurements of NH 3 desorption from Pt(111) and Pt(332) and use these results to determine elementary rate constants for desorption from steps, from (111) terrace sites and for diffusion on (111) terraces. Modeling the extracted rate constants with transition state theory, we find that conventional models for partition functions, which rely on uncoupled degrees of freedom (DOFs), are not able to reproduce the experimental observations. The results can be reproduced using a more sophisticated partition function, which couples DOFs that are most sensitive to NH 3 translation parallel to the surface; this approach yields accurate values for the NH 3 binding energy to Pt(111) (1.13 ± 0.02 eV) and the diffusion barrier (0.71 ± 0.04 eV). In addition, we determine NH 3 's binding energy preference for steps over terraces on Pt (0.23 ± 0.03 eV). The ratio of the diffusion barrier to desorption energy is ∼0.65, in violation of the so-called 12% rule. Using our derived diffusion/desorption rates, we explain why established rate models of the Ostwald process incorrectly predict low selectivity and yields of NO under typical reactor operating conditions. Our results suggest that mean-field kinetics models have limited applicability for modeling the Ostwald process.

We present the development and the first application of an optical sensor system that allows single-cycle determination of methane (CH 4 ) concentration inside internal combustion (IC) engines. We use non-dispersive infrared absorption spectroscopy to detect the CH 4 density with a time resolution up to 33 μs at acquisition rates of 30 kHz. The measurement scheme takes advantage of the strong temperature dependence of the absorption band applying two detection channels for CH 4 that detect different spectral regions of the ν 3 anti-symmetric C-H-stretch absorption. The strategy allows the simultaneous determination of fuel concentration as well as gas temperature. We show the proof-of-concept by validation of the measurement strategy in static pressure cell experiments as well as its application to a methane-fueled IC engine using a modified spark plug probe. Our results clearly demonstrate that it is crucial to determine the CH 4 temperature in the probe volume. Due to thermal influences of the sensor probe, the temperature needed to calculate the desired quantities (fuel density, fuel concentration) significantly differs from the gas phase temperature in the rest of the combustion chamber and estimations from standard thermodynamic models, e.g., polytropic compression, will fail.