Quantum Dynamical and isotopic effects for Hydrogen isotopes scattering at W(110) surface

Abstract

We investigate the scattering of hydrogen isotopes at the W(110) surface using both classical and quantum dynamics approaches to elucidate the role of quantum effects in this system. To characterize the scattering process we focus on key observables, including the absorption probability and diffraction channels that we evaluate at the quasi-classical and quantum levels. The quantum dynamics reveal pronounced resonance structures in the absorption curve that we rationalize in terms of diffraction-mediated selective adsorption and focused sticking mechanisms. Diffraction probabilities for reflected trajectories exhibit strong quantum effects at low incident energies, where classical dynamics underestimate the back scattering probability. These effects become less pronounced with increasing isotope mass, from hydrogen to tritium, however discrepancies between the classical and quantum description persist at low incident energies.

Figures (6)

• Figure 1: (a) 2D potential energy surface cut for H/W(110) system at a distance $z=1.1$ Å from the surface. Four high-symmetry positions are labeled: Hollow (H), short-bridge (SB), long-bridge (LB) and top (T) sites. (b) $Z$-cuts of the PES at the high-symmetry positions. Here $\bar{x}$, $\bar{y}$ and $\bar{z}$ are orthogonal cartesian coordinates. The potential energy along the minimum energy path in shown in dotted black line.
• Figure 2: Reflection (green) and absorption (blue) probabilities for H atoms scattering at W(110) surface with normal incidence as a function of incident energy $E_{\rm in}$. Dashed (solid) lines correspond to classical (quantum) results.
• Figure 3: Absorption probability as a function of the incident energy computed with MCTDH (solid blue line) and classical (dotted black line) methods for (a) hydrogen, (b) deuterium and (c) tritium isotopes. Vertical lines mark the energy transfer to ${\rm XY}$ degrees of freedom due to DMSAR (gold) and SAR (red) processes and combinations of them (green)
• Figure 4: Time resoled cumulative reflection probability for hydrogen (circles), deuterium (triangles) and tritium (squares) computed with MCTDH (green) and classical (red) methods. The incident energy in (a) (b) panels is 50 and 800 meV, respectively. The time on the abscissa is scaled as $\tau = t\sqrt{m_{\rm H}/m_{\rm i}}$ with $i={\rm H, D, T}$. Lines are guides to the eye.
• Figure 5: Energy resolved diffraction probability as a function of energy transfer to parallel (${\rm XY}$) degrees of freedom. Classical (quantum) results are shown by green (red) bars. Panels (a)-(c), (d)-(f), and (g)-(i) show results for hydrogen, deuterium, and tritium isotopes, respectively. The blue vertical lines indicate the values of the incident energy labeled at the top of each column. Since diffraction channels are discrete, the lines serve only as visual guides.