Ultrafast Molecular Transport on Carbon Surfaces: The Diffusion of Ammonia on Graphite

TL;DR

This study combines experimental neutron spectroscopy and theoretical calculations to reveal ultrafast ammonia diffusion on graphite, characterized by low activation energy and hopping motion, with implications for surface transport phenomena.

Contribution

It provides the first detailed combined experimental and theoretical analysis of ammonia diffusion on graphite, highlighting ultrafast hopping dynamics with low activation energy.

Findings

Diffusion constant of ammonia on graphite is 3.9 x 10^-8 m^2/s at 94 K

Ammonia diffuses via hopping motion on a weakly corrugated surface

Activation energy for diffusion is approximately 4 meV

Abstract

We present a combined experimental and theoretical study of the self-diffusion of ammonia on exfoliated graphite. Using neutron time-of-flight spectroscopy we are able to resolve the ultrafast diffusion process of adsorbed ammonia, NH$_3$, on graphite. Together with van der Waals corrected density functional theory calculations we show that the diffusion of NH$_3$ follows a hopping motion on a weakly corrugated potential energy surface with an activation energy of about 4 meV which is particularly low for this type of diffusive motion. The hopping motion includes further a significant number of long jumps and the diffusion constant of ammonia adsorbed on graphite is determined with $D=3.9 \cdot 10^{-8}~\mbox{m}^2 /\mbox{s}$ at 94 K.