Compaction of Porous H₂O Ice via Energetic Electrons

Here we have investigated the degree to which energetic electrons cause structural changes in microporous H2O ice using infrared and ultraviolet-visible spectroscopy as analytical tools. In these studies, we found that energetic electrons destroy both the dangling bond (DB) absorption bands, indicative of internal surface area, and the internal porosity of our samples. In addition, we find it takes about a factor of 3 higher fluence to decrease the internal pore volume by 63.2% than it does the internal surface area, which is likely because the surface area decreases by both destruction of the internal pores and also by smaller pores coalescing into large ones. Extrapolating our results to the interstellar medium (ISM), we estimate that the time needed for these processes to occur is significantly shorter than the expected lifetime of a molecular cloud, leading us to speculate that future detections of the DB absorption bands or other indicators of porosity in the ISM will be relatively rare.