posted on 2007-06-21, 00:00authored byJobin Cyriac, T. Pradeep
In this work, we have examined the diffusive mixing of chloromethanes in different molecular solids H2O,
D2O, and CH3OH by monitoring their chemical sputtering spectra due to the impact of Ar+ ions in the collision
energy range of 3−60 eV, focusing on amorphous solid water. The chemical sputtering spectra have been
monitored over the temperature window accessible by liquid nitrogen, and the coverages of the molecules of
interest and ice have been varied from one to several hundred monolayers. Instrumentation and sensitivity of
the technique have been discussed. It is found that while the diffusion of CCl4 in the molecular solids
investigated is hindered, other choloromethanes such as CHCl3 and CH2Cl2 undergo diffusive mixing over
the same temperature range. Quantitatively, while ∼4 monolayers (ML) of ice are found to block CCl4 diffusion,
the numbers are ∼250 and ∼600 ML for CHCl3 and CH2Cl2, respectively. Crystallinity of ice does not have
any effect on the diffusivity of water molecules when it is deposited below the chloromethanes. The effect
of substrate was insignificant, and the rise in temperature increased diffusive mixing wherever the process
was observed at a lower temperature.