  Amorphous solid water (ASW) is one of the most widely studied solid phase
systems. A better understanding of the nature of inter- and intramolecular
forces in ASW is, however, still required to correctly interpret the catalytic
role of ASW in the formation and preservation of molecular species in
environments such as the icy surfaces of Solar System objects, on interstellar
icy dust grains and potentially even in the upper layers of the Earth's
atmosphere. In this work, we have systematically exposed porous ASW (pASW) to
mid-infrared radiation generated by a free-electron laser at the HFML-FELIX
facility in the Netherlands to study the effect of vibrational energy injection
into the surface and bulk modes of pASW. During multiple sequential
irradiations on the same ice spot, we observed selective effects both at the
surface and in the bulk of the ice. Although the density of states in pASW
should allow for a fast vibrational relaxation through the H-bonded network,
part of the injected energy is converted into structural ice changes as
illustrated 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, ice morphology, and ice composition.
