The Dynamics of Highly Vibrationally Excited CO Scattered from Metal Surfaces

by Roman Jonathan Viktor Wagner
Doctoral thesis
Date of Examination:2019-04-09
Date of issue:2019-04-26
Advisor:Prof. Dr. Alec Wodtke
Referee:Prof. Dr. Alec M. Wodtke
Referee:Prof. Dr. Dirk Schwarzer
Referee:Prof. Dr. Jörg Behler
Referee:Prof. Dr. Burkhard Geil
Referee:Prof. Dr. Theofanis N. Kitsopoulos
Referee:Prof. Dr. Jürgen Troe
Persistent Address: http://dx.doi.org/10.53846/goediss-7411

 

 

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Abstract

English

Supersonic molecular beams of highly vibrationally excited CO are scattered from atomically clean Au(111) and Ag(111) surfaces. Specifically, incident CO is prepared in the (v = 17, J = 0) state of the electronic ground state. Scattered molecules are detected quantum state-selectively by means of resonance-enhanced multi-photon ionization. Final vibrational state distributions and rotational state distributions are presented as well as time-of-flight distributions and angular distributions. Rotationally hot scattering products, narrow angular distributions, and final translational energies consistent with the Baule limit indicate a direct scattering mechanism. The vibrational relaxation probability of CO(v = 17) at Ag(111) is higher than that at Au(111). For both metals, the vibrational relaxation probability increases with incidence translational energy. The incidence translational energy dependence is more pronounced for Au(111) than for Ag(111). The comparison to previously studied molecule-surface systems—including two molecules (CO and NO), two surfaces (gold and silver), and various incidence vibrational excitations (ranging from v = 2 to v = 17)—reveals a unifying trend, according to which the vibrational relaxation probability depends on both the work function of the surface and the electron binding energy of the molecule. This strongly suggests that an electron transfer process is essential to the electronically non-adiabatic coupling between molecular vibration and electronic degrees of freedom of the surface. Thus, for a single-bounce collision event with a metal surface, the vibrational relaxation probability of a diatomic molecule can be predicted simply by evaluating energetic quantities characterizing the isolated molecule and surface. This allows easy identification of molecule-surface systems in which non-adiabatic surface dynamics are likely to be governed by electron transfer.
Keywords: Dynamics at Surfaces; Molecular Beam Surface Scattering; Energy Transfer; Highly Vibrationally Excited CO; Vibrational Relaxation; Electron Transfer; REMPI Spectroscopy; Stark Deceleration
 
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