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To investigate the decomposition mechanisms of adsorbed H2O molecules as a monolayer on the surface of forsterite glass, we performed molecular dynamics calculations. The decomposition phenomenon of H2O molecules is observed at temperatures above 200 K. The equilibrium rate of the decomposed H2O increases as the temperature increases and approaches 1.0 at temperatures above 500 K. The decomposed hydrogen forms MgOxHy or SiO4Hz structures with MgOx or SiOz units in forsterite glass. The processes of decomposition and reformation of the structure units on the surface of forsterite glass have important implications for chemical evolution in interstellar spaces.

To investigate the effects of forsterite structure on processes of H2O decomposition and proton diffusion, we performed molecular dynamics calculations on forsterites in glassy and crystalline states. The result shows that the decomposition rate of H2O on forsterite in the glassy state is higher than that in crystalline state in a temperature range of 200 to 400 K. Furthermore, the decomposed proton permeates into the internal part of glassy forsterite through hopping, whereas no permeation was observed for the crystalline state. These results suggest that the glassy structure of forsterite is an important factor for chemical evolution processes in interstellar spaces.