Abstract
Dissociative chemisorption of O2 on the Al(111) surface represents an extensively studied prototype for understanding the interaction between O2 and metal surfaces. It is well known that the experimentally observed activation barrier for O2 dissociation is not captured by conventional density functional theory. The interpretation of this barrier as a result of spin transitions along the reaction path has been challenged by recent embedded correlated wave function (ECW) calculations that naturally yield an adiabatic barrier. However, the ECW calculations have been limited to a static analysis of the reaction pathways and have not yet been tested by dynamics simulations. We present a global six-dimensional potential energy surface (PES) for this system parametrized with ECW data points. This new PES provides a reasonable description of the site-specific and orientation-dependent activation barriers. Quasi-classical trajectory calculations on this PES semiquantitatively reproduce both the observed translational energy dependence of the sticking probability and steric effects with aligned O2 molecules.
Highlights
A s the initial and often rate-determining step in heterogeneous catalysis, dissociative chemisorption of molecules on metal surfaces continues to attract much attention
Energy- and quantum-state-resolved initial sticking probabilities have been measured for various molecules using the molecular beam approach under ultrahigh vacuum.[1−3] These measurements are complemented by theoretical investigations of dissociation and scattering dynamics in high-dimensional spaces,[4−8] which have been almost exclusively based on a density functional theory (DFT) characterization of the electronic structure
Theoretical studies based on Kohn−Sham DFT within the generalized gradient approximation (GGA) found no adiabatic barrier for the dissociative process,[15−17] in sharp contrast with the experimental findings
Summary
Included the nonadiabatic transitions between the two states using a surface-hopping (SH) approach and obtained a qualitatively similar result as that on the single triplet PES.[20,21]. Taking advantage of the flexible and analytical FPLEPS function, we were able to construct a global 6D PES with just 700 previously computed ECW points, largely reproducing the site-specific and orientation-dependent activation barriers and the anisotropy in angular degrees of freedom found in the original ECW studies.[27,31] Dynamics based on this new PES semiquantitatively reproduce the translational energy dependence in the experimental data, capturing the activated nature suggested in experimental work.[13,30] In addition, O2 initially aligned parallel to the surface is more reactive than the perpendicular one as a result of an overall lower barrier by ∼0.1 eV for the parallel orientation, again in good agreement with experiment.[30] Such a steric effect is always present as the incident angle varies from 0 to 40° with respect to surface normal, while the sticking probability decreases monotonically, in qualitative agreement with experiment.[30] Despite these successes, quantitatively, the onset of sticking is shifted to higher energies by roughly ∼0.05 eV compared with experiment[13,30] and does not obey the normal energy scaling law,[30] presumably due to the uncertainty of the barrier heights in the ECW calculations and approximation in the FPLEPS function. Details of ECW theory, PES representation, as well as the quasi-classical trajectory calculations. (PDF)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
