Physical properties and photochemistry of interstellar ice analogs furnishing complex organic molecules

The presentation covers the topics reported in our recent work published in Nature Rev. Chem. [1]. It covers 50 years of experiments dedicated to simulate radiation and thermally driven processes that occur on icy dust particles in space. The interstellar and protoplanetary ice composition is dominated by water and often contains CO, CO2, CH4, CH3OH, NH3, OCN-, OCS, and probably larger species which await identification. The harsh conditions in space (ultra-high vacuum, cryogenic temperatures, and radiation) are mimicked in the laboratory. UV photons/X-rays/ions impact on the ice covering microscopic pre-cometary dust particles in dense interstellar clouds and protoplanetary disks prior to the formation of cometesimals by agglomeration of the icy dust. Laboratory results show that radiation produces radicals and reactive species changing the initial composition of the ice to form complex organic molecules (COMs) of prebiotic interest (among them are several amino acids, nitrogen-heterocycles related to nucleobases, and sugars). Many of these molecules were also identified in Rosetta comet 67P, and infrared spectra of Ryugu samples delivered by Hayabusa2 are strikingly similar to those of refractory residues retrieved at room temperature after warmup of the irradiated ice [2].  

First, recent experimental results on ice properties (density, infrared spectroscopy, optical constants, morphology) supported by DFT calculations will be presented with important updated values of the ice density and infrared band strengths. This allows a proper column density estimation of the various molecular ice components. For instance, the commonly used band strength of water ice was significantly lower than the actual value and did not take into account the variations due to ice temperature. Second, recent results obtained in our laboratory regarding COMs formation by ultraviolet irradiation of interstellar ice analogs will be unveiled. We will propose formation mechanisms of the heterocycles identified in the residues made by ice processing. Another talk by H. Carrascosa will discuss in more detail the important role played by water molecules in the ice chemistry that enables the synthesis of prebiotic species.      

References


[1]    G. M. Muñoz Caro, H. Carrascosa, & R. Martín-Doménech “Photochemistry of interstellar ice forming complex organic molecules”, 2025, Nature Rev. Chem. 9, 537


[2]    J. Mathurin, et al. ¨AFM-IR nanospectroscopy of nanoglobule-like particles in Ryugu