1. Understanding chemical reactions at the molecular level 2. Molecular collisions 3. Introduction to reactive molecular collisions 4. Scattering as a probe of collision dynamics 5. Introduction to polyatomic dynamics 6. Structural considerations in the calculation of reaction rates 7. Photoselective chemistry: access to the transition state region 8. Chemistry in real time 9. State-changing collisions: molecular energy transfer 10. Stereodynamics 11. Dynamics in the condensed phase 12. Dynamics of gas-surface interactions and reactions.

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Molecular reaction dynamics

Molecular Reaction Dynamics: Frontmatter

Oxygen chemisorption on metal surfaces: General trends for Cu, Ni and Ag

Molecular beam experiments on model catalysts

NO adsorption on metal surfaces has been studied extensively due to its important role in many catalytic processes In the past, it was recognized that the tendency for a metal surface to dissociate NO depends on its position in the periodic table, but little was understood about the dissociation process itself Recent experimental and theoretical studies have shown that this view is oversimplified In addition to the distinction between molecular and dissociative adsorption on surfaces, the structure of NO on metal surfaces has also been the subject of detailed study and debate It is therefore timely to update our ideas about NO adsorption and reactivity Here we examine the structure of NO on surfaces, in particular the break-down of vibrational assignments and we look at how these assignments can be improved The NO dissociation process is also discussed along with the formation, and reactions, of the NO dimer, (NO)(2), on some metal surfaces

NO Chemisorption and Reactions on Metal Surfaces: A New Perspective

Molecules adsorbed on a surface are known to show preferential orientations, and in particular, the interaction potential between a linear molecule and a surface depends on the orientation of the molecular axis. But the fact that the molecules eventually adsorbed are orientated with respect to the surface is not evidence that the dynamics of gas–surface interactions is governed by the initial molecular orientation in the gas phase. For example at very low velocities the molecule might achieve its optimum orientation adiabatically during its approach to the surface. Dependence of scattering dynamics on molecular orientation can also be degraded as a result of surface structure and surface vibrations. There have been, experimental studies, however, which suggest that orientational or steric effects could influence gas–surface scattering1–4. Thus, the much larger rotational excitation for NO- than for N2-scattering from Ag(lll) indicates that large anisotropies can occur in a potential for gas–surface dynamics (G. O. Sitz et al. manuscript in preparation). The double rotational rainbow observed in the rotational state distribution for NO/Ag(111) (refs 3 and 4) can also be interpreted as a manifestation of this anisotropy5–9. These studies all indicate that steric effects could be important and here we report on scattering of orientated NO from Ag(111) to provide direct experimental evidence for the importance of such effects in gas–surface interactions.

Observation of steric effects in gas–surface scattering

The adsorption probability for NO/Pt(111) is highest for an initial orientation with the N end of the molecule towards the surface This steric effect in the adsorption brings about a large averaged steric effect in the direct scattering, which is amplified by the fact that the adsorption probability is very high In case of direct scattering an N-end collision results in a smaller reflection angle than an O-end collision

Steric effects for NO/Pt(111) adsorption and scattering.

Differential trapping probabilities and desorption of physisorbed molecules: Application to NO/Ag(111)

A pulsed supersonic and cold oriented beam of NO molecules is incident upon the (111) face of clean Ag and Pt single crystal surfaces. The steric effect in the scattered density distributions is determined by a quadrupole mass spectrometer. It is found that the steric effect in the peak in the distribution of direct inelastically scattered molecules depends linearly on the reflection angle. In all circumstances O‐end collisions lead to scattering angles more inclined towards the surface than N‐end collisions. For the Pt(111) surface a much stronger steric effect is measured than for the Ag(111) surface. The steric effect seems to scale with the incident normal velocity. These strong steric effects can be explained by the larger trapping probability for the N‐end orientation and a leverage effect due to the high trapping probability.

E. W. Kuipers

Papers

Observation of steric effects in gas–surface scattering

Steric effects for NO/Pt(111) adsorption and scattering.

Differential trapping probabilities and desorption of physisorbed molecules: Application to NO/Ag(111)

Direct inelastic scattering of oriented NO from Ag(111) and Pt(111)

Molecular beam apparatus to study interactions of oriented NO and surfaces