PNNL

Abstract

Desorption of carbon tetrachloride from beneath an amorphous solid water (ASW) overlayer is explored utilizing a combination of temperature programmed desorption and infrared spectroscopy. Otherwise inaccessible information about the dewetting and crystallization of ASW is revealed by monitoring desorption of the CCl4 underlayer. The desorption maximum of CCl4 on graphene occurs at ~140 K. When ASW wets the CCl4 no desorption below 140 K is observed. However, the mobility of the water molecules increases with ASW deposition temperature, leading to a thermodynamically driven dewetting of water from the hydrophobic CCl4 surface. This dewetting exposes some CCl4 to the ambient environment, allowing unhindered desorption of CCl4 below 140 K. When ASW completely covers the underlayer, desorption of CCl4 is delayed until crystallization induced cracking of the ASW overlayer opens an escape path to the surface. The subsequent rapid episodic release of CCl4 is termed a “molecular volcano”. Reflection adsorption infrared spectroscopy (RAIRS) measurements indicate that the onset and duration of the molecular volcano is directly controlled by the ASW crystallization kinetics.