Dissociative Sticking Probability of Methane on Pt(110)-(2×1)

Abstract

In this work, we revisit the dissociative sticking of methane on Pt(110)-(2×1) using quasi-classical trajectory (QCT) calculations and supersonic molecular beam (SMB) experiments. Experimentally, we apply the King and Wells method and the reflection absorption infrared spectroscopy (RAIRS) technique to measure the initial dissociative sticking probability,S0. Our QCT calculations make use of a reactive force field (RFF) based on density functional theory (DFT) total energy results. We compare our QCT results forS0with experiments and with density functional molecular dynamics (DFMD) data available for CHD3(v= 0). The fact that our QCT RFF-based approach is computationally much cheaper than DFMD allows us to integrate a much larger number of trajectories for longer interaction times. Thus, we can significantly extend the previously reported comparison of QCT-DFMD and experimental results, for CHD3(v= 0), CH4(v= 0), and CH4(ν3= 1) to lower incident energies,Ei(≥ 0.2 eV), and surface temperatures,Ts(down to 120 K). Our QCT results and the SMB experimental data agree qualitatively with theory, underestimating the experimental results by a factor of ∼2-3. Our calculations shed light on the fate of the surprisingly large fraction of methane molecules, which remain trapped on the surface for much more than 1 ps (and therefore can hardly be studied using DFMD) forEivalues as large as ∼1 eV. We show that the contribution of trapped molecules toS0is negligible over a wide range of initial conditions, due to two reasons: (i) the barrier for dissociation is larger than that for desorption on all surface sites and (ii) trapped molecules spend most of the time on top of the valley Pt atoms, where the physisorption well is the deepest but the energy barrier for dissociation is the highest.