Temperature-Programmed Desorption of prebiotic molecules from dust in simulated space conditions

Millimeter and centimeter observations are discovering an increasing number of interstellar complex organic molecules (iCOMs) in a large variety of star forming sites [1, 2, 3]. In protoplanetary disks, it is difficult to observe iCOMs in the gas phase because the region where temperature is high enough for the thermal desorption is too close to the star (< 5 au). A new perspective is provided by objects such as the FU Ori systems in which the young central star undergoes a sudden increase in brightness which leads to a heating of the disk and a quick expansion of the snow lines to large radii. This phenomenon was observed in the system V883 Ori [4], where five iCOMs thermally desorbed from the disk were detected [5]. In laboratory, it is possible to simulate the thermal desorption process and UV irradiation of iCOMs deriving important parameters such as the thermal desorption temperatures and binding energies. We will report laboratory results on temperature-programmed desorption (TPD) analysis of pure formamide ice and in the presence of TiO2 dust, before and after UV irradiation [6]. Pure formamide desorbs at 220 K in high vacuum regime, while its photoproducts NH2, HCO and CH2NO desorb at 180 K. Formamide desorption fromTiO2 dust occurs at higher temperature (250 K) because the molecule interacts and diffuses through the grains. This is confirmed by the different value of the binding energy that we found. We report also new results about thermal desorption of ice mixtures of acetaldehyde and acetonitrile from olivine grains on which the molecules are deposited at 10 K. We observed a second desorption peak that shows up as a shoulder related with a higher desorption temperature. These studies offer support to observational data and can improve our understanding of the role of grain surface in enriching the gas phase chemistry in space.

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