Chapter 10
Surface-Aligned Femtochemistry: Molecular
Reaction Dynamics on Oxide Surfaces
Mihai E. Vaida and Thorsten M. Bernhardt
Abstract In this contribution the application of ultrafast laser pulses to reveal the
dynamics of chemical reactions on metal oxide surfaces will be discussed. A combination of an optical pump-probe configuration with time-of-flight mass spectrometry is employed to monitor the mass and the relative velocity of intermediates and
products of a photoinduced surface reaction in real time. Starting from a well defined
reactant adsorption geometry representing the initial “collision complex” of the reactive encounter, this approach enables the observation of the coherent nuclear motion through the transition state to the emerging reaction products and thus provides
insight into the elementary steps of complex surface chemical reaction mechanisms.
Results will be presented for the application of this technique to the photodissociation dynamics of methyl iodide and methyl bromide adsorbed on magnesia ultrathin
films on a Mo(100) single crystal surface.
10.1 Introduction
The influence of a solid support on the dynamics of a molecular encounter is of
fundamental interest to all aspects of surface chemistry and catalysis [1, 2]. An issue of central importance in this respect is the geometrical alignment of the initial
collision complex, which determines the passage through the transition state and
ultimately the outcome of the desired chemical reaction [3, 4]. The motion involved
in this process occurs on the ultrafast timescale of nuclear movement and its understanding is fundamental to the perception of chemical reaction mechanisms on
surfaces of, e.g., catalytic materials. However, in order to be able to unravel the
decisive molecular dynamics, the averaging over an ensemble of impact parameters and trajectories originating from variations in the starting geometry has to be
minimized [5].
In gas phase experiments this can be realized by employing van der Waals complexes of reactants with defined geometry that are prepared in a supersonic molecM.E. Vaida · T.M. Bernhardt (B)
Institute of Surface Chemistry and Catalysis, University of Ulm, Albert-Einstein-Allee 47,
89069 Ulm, Germany
e-mail: thorsten.bernhardt@uni-ulm.de
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_10,
© Springer International Publishing Switzerland 2014
231
Surface-Aligned Femtochemistry: Molecular
Reaction Dynamics on Oxide Surfaces
Mihai E. Vaida and Thorsten M. Bernhardt
Abstract In this contribution the application of ultrafast laser pulses to reveal the
dynamics of chemical reactions on metal oxide surfaces will be discussed. A combination of an optical pump-probe configuration with time-of-flight mass spectrometry is employed to monitor the mass and the relative velocity of intermediates and
products of a photoinduced surface reaction in real time. Starting from a well defined
reactant adsorption geometry representing the initial “collision complex” of the reactive encounter, this approach enables the observation of the coherent nuclear motion through the transition state to the emerging reaction products and thus provides
insight into the elementary steps of complex surface chemical reaction mechanisms.
Results will be presented for the application of this technique to the photodissociation dynamics of methyl iodide and methyl bromide adsorbed on magnesia ultrathin
films on a Mo(100) single crystal surface.
10.1 Introduction
The influence of a solid support on the dynamics of a molecular encounter is of
fundamental interest to all aspects of surface chemistry and catalysis [1, 2]. An issue of central importance in this respect is the geometrical alignment of the initial
collision complex, which determines the passage through the transition state and
ultimately the outcome of the desired chemical reaction [3, 4]. The motion involved
in this process occurs on the ultrafast timescale of nuclear movement and its understanding is fundamental to the perception of chemical reaction mechanisms on
surfaces of, e.g., catalytic materials. However, in order to be able to unravel the
decisive molecular dynamics, the averaging over an ensemble of impact parameters and trajectories originating from variations in the starting geometry has to be
minimized [5].
In gas phase experiments this can be realized by employing van der Waals complexes of reactants with defined geometry that are prepared in a supersonic molecM.E. Vaida · T.M. Bernhardt (B)
Institute of Surface Chemistry and Catalysis, University of Ulm, Albert-Einstein-Allee 47,
89069 Ulm, Germany
e-mail: thorsten.bernhardt@uni-ulm.de
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_10,
© Springer International Publishing Switzerland 2014
231