IRFEL Selective Irradiation of Amorphous Solid Water: from Dangling to Bulk Modes

Amorphous solid water (ASW) is one of the mostwidely studied solid phase systems. A better understanding of thenature of inter- and intramolecular forces in ASW is, however, stillrequired to correctly interpret the catalytic role of ASW in theformation and preservation of molecular species in environmentssuch as the icy surfaces of Solar System objects, on interstellar icydust grains, and potentially even in the upper layers of the Earth'satmosphere. In this work, we have systematically exposed porousASW (pASW) to mid-infrared radiation generated by a free-electronlaser at the HFML-FELIX facility in The Netherlands to study theeffect of vibrational energy injection into the surface and bulk modesof pASW. During multiple sequential irradiations on the same icespot, we observed selective effects both at the surface and in the bulkof the ice. Although the density of states in pASW should allow for afast vibrational relaxation through the H-bonded network, part of the injected energy is converted into structural ice changes asillustrated by the observation of spectral modifications when performing Fourier transform infrared spectroscopy in reflection-absorption mode. Future studies will include the quantification of such effects by systematically investigating ice thickness, icemorphology, and ice composition

Automated summary

Amorphous solid water is one of the most widely studied solid phase systems, and understanding the nature of inter- and intramolecular forces in ASW is crucial for interpreting its catalytic role in environments. Experiments with mid-infrared radiation demonstrated the selective effects of vibrational energy injection on both the surface and bulk of pASW.