PNNL

Abstract

We compare the adsorption, desorption, trapping, and release of Ar, N2, O2, CO, and CH4, by dense (non-porous) and highly porous amorphous solid water (ASW) films. Molecular beam deposition techniques were used to control the porosity of the vapor deposited ASW thin films. Experiments where the gas species was deposited on top and underneath of dense and porous ASW were conducted. The porous films were found to adsorb between 20 and 50 times more gas than the dense films. The desorption temperature of the adsorbed gas was also dependent on the porosity of the ASW film. The differences between desorption from porous and dense ASW films are attributed to differences in their ability to trap weakly physisorbed gases. The results were largely independent of the gas studied confirming that the adsorption and trapping of gases is dominated by the ASW porosity. These findings show that laboratory studies must account for the growth conditions and their effects on ASW morphology in order accurately predict the properties of astrophysical ices.