Probing the structure of prebiotic ice

M. A. Wilson, A. Pohorille, P. Jenniskens and D. Blake, Origins of Life and Evolution of Biosphere, 25, 3-19 (1995).

Abstract:

Computer simulations of bulk and vapor deposited amorphous ices are presented. The structure of the bulk low density amorphous ice is in good agreement with experiments on bulk pressure disordered amorphous ice. Both the low density bulk ice and the vapor deposited ices exhibit strong tetrahedral ordering. Vapor deposition of hot (300 K) water molecules onto a cold (77 K) substrate yields less porous ices than deposition of cold (77 K) water molecules onto a cold substrate. Both vapor deposited ices are more porous than the bulk amorphous ice. The structure of bulk high density amorphous ice is only in fair agreement with experimental results. Attempts to simulate high density amorphous ice via vapor deposition were not successful. Electron diffraction results on vapor deposited amorphous ice indicate that the temperature of the nucleation of the cubic phase depends upon the amount of time between the deposition and the start of the heating. This is interpreted to mean that freshly deposited ice layers reconstruct on times of the order of hours. The relevance of the structure of amorphous ice to the origin of simple organic matter on the early Earth is discussed.