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Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH4on Ni(111). IR-IR double resonance excitation in a molecular beam was used to prepare CH4 in three different vibrational symmetry components, A1, E, and F2, of the 2ν3 antisymmetric stretch overtone vibration as well as in the ν1+ν3symmetric plus antisymmetric C-H stretch combination band of F2 symmetry. The quantum state specific dissociation probability S0 (sticking coefficient) was measured for each of the four vibrational states by detecting chemisorbed carbon on Ni(111) as the product of CH4 dissociation by Auger electron spectroscopy. We observe strong mode specificity, where S0 for the most reactive state ν1+ν3 is an order of magnitude higher than for the least reactive, more energetic 2ν3-E state. Our first principles quantum scattering calculations show that as molecules in the ν1 state approach the surface, the vibrational amplitude becomes localized on the reacting C-H bond, making them very reactive. This behavior results from the weakening of the reacting C-H bond as the molecule approaches the surface, decoupling its motion from the three non-reacting C-H stretches. Similarly, we find that overtone normal mode states with more ν1 character are more reactive: S0 (2ν1) > S0 (ν1 + ν3) > S0 (2ν3). The 2ν3eigenstates excited in the experiment can be written as linear combinations of these normal mode states. The highly reactive 2ν1 and ν1 + ν3 normal modes, being of A1 and F2 symmetry, can contribute to the 2ν3-A1 and 2ν3-F2 eigenstates, respectively, boosting their reactivity over the E component, which contains no ν1 character due to symmetry. [ABSTRACT FROM AUTHOR]

Quantum state resolved reactivity measurements probe the role of vibrational symmetry on the vibrational activation of the dissociative chemisorption of CH 4 on Ni(111). IR-IR double resonance excitation in a molecular beam was used to prepare CH 4 in three different vibrational symmetry components, A 1 , E, and F 2 , of the 2ν 3 antisymmetric stretch overtone vibration as well as in the ν 1 +ν 3 symmetric plus antisymmetric C-H stretch combination band of F 2 symmetry. The quantum state specific dissociation probability S 0 (sticking coefficient) was measured for each of the four vibrational states by detecting chemisorbed carbon on Ni(111) as the product of CH 4 dissociation by Auger electron spectroscopy. We observe strong mode specificity, where S 0 for the most reactive state ν 1 +ν 3 is an order of magnitude higher than for the least reactive, more energetic 2ν 3 -E state. Our first principles quantum scattering calculations show that as molecules in the ν 1 state approach the surface, the vibrational amplitude becomes localized on the reacting C-H bond, making them very reactive. This behavior results from the weakening of the reacting C-H bond as the molecule approaches the surface, decoupling its motion from the three non-reacting C-H stretches. Similarly, we find that overtone normal mode states with more ν 1 character are more reactive: S 0 (2ν 1 ) > S 0 (ν 1 + ν 3 ) > S 0 (2ν 3 ). The 2ν 3 eigenstates excited in the experiment can be written as linear combinations of these normal mode states. The highly reactive 2ν 1 and ν 1 + ν 3 normal modes, being of A 1 and F 2 symmetry, can contribute to the 2ν 3 -A 1 and 2ν 3 -F 2 eigenstates, respectively, boosting their reactivity over the E component, which contains no ν 1 character due to symmetry.

The dissociation of methane is not only an important reaction step in catalytic processes, but also of fundamental interest. Dynamical effects during the dissociative chemisorption of methane on metal surfaces cause significant differences in computed reaction rates, compared to what is predicted by typical transition state theory (TST) models. It is clear that for a good understanding of the catalytic activation of methane dynamical simulations are required. In this paper, a general blueprint is provided for performing dynamical simulations of the dissociative chemisorption of methane on metal surfaces, by employing either the quasi-classical trajectory or ring polymer molecular dynamics approach. If the computational setup is constructed with great care-since results can be affected considerably by the setup - chemically accurate predictions are achievable. Although this paper concerns methane dissociation, the provided blueprint is, so far, applicable to the dissociative chemisorption of most molecules. [ABSTRACT FROM AUTHOR]

We present a comparison of ab initio molecular dynamics calculations for CHD3 dissociation on Pt(111) using the Perdew, Burke and Ernzerhof (PBE) functional and a specific reaction parameter (SRP) functional. Despite the two functionals predicting approximately the same activation barrier for the reaction, the calculations using the PBE functional consistently overestimate the experimentally determined dissociation probability, whereas the SRP functional reproduces the experimental values within a chemical accuracy (4.2 kJ/mol). We present evidence that suggests that this difference in reactivity can at least in part be attributed to the presence of a van derWaals well in the potential of the SRP functional which is absent from the PBE description. This leads to the CHD3 molecules being accelerated and spending less time near the surface for the trajectories run with the SRP functional, as well as more energy being transferred to the surface atoms.We suggest that both these factors reduce the reactivity observed in the SRP calculations compared to the PBE calculations. [ABSTRACT FROM AUTHOR]

Understanding the microscopic mechanism of molecule–surface interaction is of great importance in the study of chemical dynamics. Yet, it remains challenging to experimentally acquire quantum state resolved results, particularly the results related to different degrees of freedom of the reactants. Here, we report the design and performance of a new apparatus for molecule–surface dynamics studies, which enable the measurement of quantum state-resolved adsorption. A continuous narrow-linewidth infrared laser source and molecular beam unit were developed and employed in this new apparatus to achieve independent control on different degrees of freedom (translation, vibration, and rotation) of the molecule. Preliminary results on hydrogen and hydrogen chloride adsorption on the Cu (111) surface were also presented. [ABSTRACT FROM AUTHOR]

To understand the dynamics of H3O+ formation, we report a combined experimental–theoretical study of the rovibrationally state-selected ion–molecule reactions H2O+(X2B1; v1+v2+v3+; NKa+Kc++) + H2 (D2) → H3O+ (H2DO+) + H (D), where (v1+v2+v3+) = (000), (020), and (100) and NKa+Kc++ = 000, 111, and 211. Both quantum dynamics and quasi-classical trajectory calculations were carried out on an accurate full-dimensional ab initio global potential energy surface, which involves nine degrees of freedom. The theoretical results are in good agreement with experimental measurements of the initial state specific integral cross-sections for the formation of H3O+ (H2DO+) and thus provide valuable insights into the surprising rotational enhancement and vibrational inhibition effects in these prototypical ion–molecule reactions that play a key role in the interstellar generation of OH and H2O species. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various topics within the issue including methane chemisorption on metal surfaces, polyatomic dissociative chemisorption and reactive scattering of hydrogen.

We present a tutorial review of our quantum state resolved experiments designed to study gas–surface reaction dynamics. The combination of a molecular beam, state specific reactant preparation by infrared laser pumping, and ultrahigh vacuum surface analysis techniques make it possible to study chemical reactivity at the gas–surface interface in unprecedented detail. We describe the experimental techniques used for state specific reactant preparation and for detection of surface bound reaction products developed in our laboratory. Using the example of the reaction of methane on Ni and Pt surfaces, we show how state resolved experiments uncovered clear evidence for vibrational mode specificity and bond selectivity, as well as steric effects in chemisorption reactions. The state resolved experimental data provides valuable benchmarks for comparison with theoretical models for gas–surface reactivity aiding in the development of a detailed microscopic understanding of chemical reactivity at the gas–surface interface. [ABSTRACT FROM AUTHOR]

The dream of theoretical surface chemistry is to predict the outcome of reactions in order to find the ideal catalyst for a certain application. Having a working ab initio theory in hand would not only enable these predictions but also provide insights into the mechanisms of surface reactions. The development of theoretical models can be assisted by experimental studies providing benchmark data. Though for some reactions a quantitative agreement between experimental observations and theoretical calculations has been achieved, theoretical surface chemistry is in general still far away from gaining predictive power. Here we review recent experimental developments towards the understanding of surface reactions. It is demonstrated how quantum-state resolved scattering experiments on reactive and nonreactive systems can be used to test front-running theoretical approaches. Two challenges for describing dynamics at surfaces are addressed: nonadiabaticity in diatomic molecule surface scattering and the increasing system size when observing and describing the dynamics of polyatomic molecules at surfaces. Finally recent experimental studies on reactive systems are presented. It is shown how elementary steps in a complex surface reaction can be revealed experimentally. [ABSTRACT FROM AUTHOR]