The Molecular Volcano: Abrupt CCl₄ Desorption Driven by the Crystallization of Amorphous Solid Water

The desorption kinetics of molecular beam deposited ultrathin films of CCl₄ and amorphous solid water (ASW) are studied. Overlayers of ASW impede CCl₄ desorption until the onset of crystallization, whereupon the CCl₄ desorbs abruptly. The abrupt desorption occurs through connected pathways that are formed in the water overlayer during the nucleation and growth of crystalline ice from ASW. The onset of the abrupt desorption corresponds to the threshold for dynamic percolation. As the crystallization proceeds, the number of connected pathways rapidly increases, giving rise to the episodic release of CCl₄.