Synthesis of Complex Organic Molecules in Soft X-Ray Irradiated Ices

Abstract

We study the chemical evolution of H 2 O:CO:NH 3 ice mixtures irradiated with soft X-rays, in the range 250 − 1250 eV. We identify many nitrogen-bearing molecules such as e.g., OCN − , NH + 4 , HNCO, CH 3 CN, HCONH 2 , and NH 2 COCONH 2 . Several infrared features are compatible with glycine or its isomers.During the irradiation, we detected through mass spectroscopy many species desorbing the ice. Such findings support either the infrared identifications and reveal less abundant species with not clear infrared features. Among them, m/z = 57 has been ascribed to methyl isocyanate (CH 3 NCO), a molecule of prebiotic relevance, recently detected in protostellar environments.During the warm up after the irradiation, several infrared features including 2168 cm −1 band of OCN − , 1690 cm −1 band of formamide, and the 1590 cm −1 band associated to three different species, HCOO − , CH 3 NH 2 and NH + 3 CH 2 COO survive up to room temperature. Interestingly, many high masses have been also detected. Possible candidates are methyl-formate, (m/z = 60, HCOOCH 3 ), ethanediamide (m/z = 88, NH 2 COCONH 2 ), and N-acetyl-L-aspartic acid (m/z = 175). This latter species is compatible with the presence of the m/z = 43, 70 and 80 fragments.Photo-desorption of organics is relevant for the detection of such species in the gas-phase of cold environments, where organic synthesis in ice mantles should dominate. We estimate the gas-phase enrichment of some selected species in the light of a protoplanetary disc model around young solartype stars.

Photochemistry and desorption induced by X-rays in water rich astrophysical ice analogs: implications for the moon Enceladus and other frozen space environments

“…Recently, another experimental study employing X-ray photolysis of NH 3 -rich ices have also observed the formation of OCN À , NH 4 + , HCONH 2 , and other species including some IR features compatible with glycine or its isomers. 26 Employing photons between 250 to 1250 eV (with maximum at 700 eV) and combined infrared measurements with mass The infrared analysis of organic residue at room temperature indicates the presence of even more complex species, including HMT (hexamethylenetetramine), carboxylic salts and amides. The presence of HMT, amides and related species in irradiated NH 3 -rich ices by strong ionizing eld was also observed by Pilling et al, 16 employing cosmic ray analogs with energies in the range of MeV.…”

“…Ciaravella et al, 26 have determined the photodesorption yield for some new produced species, during X-ray photolysis of NH 3 -rich ices at 12 K, by employing a combination of mass spectrometry and infrared techniques. The authors, employing a broadband X-rays beam in the range between 250 and 1250 eV (with maximum at 700 eV) have obtained the following values, for some selected produced species (they detected more than 40 species), 1.94 Â 10 À5 and 3.17 Â 10 À5 for CH 3 NH 2 and HNCO, respectively.…”

“…Previous experiments also employing X-rays on analogous astrophysical ices have also shown the importance of such ionizing agent in the physicochemical processing of the frozen sample. 10,[21][22][23][24][25][26] Section 2 describes the experimental setup and sample properties. The results and the analysis of the infrared spectra of both samples are given the Section 3.…”

Toward the RNA-World in the Interstellar Medium—Detection of Urea and Search of 2-Amino-oxazole and Simple Sugars

“…Indeed, it has been proposed that CH 2 (OH)CHO formation is boosted by ice irradiation (Biver et al, 2015). This irradiation can either be in the form of UV photons, X-rays, or cosmic rays, since all types of irradiation have the same effect on the final chemical composition of the ices (Muñoz Caro et al, 2014;de Marcellus et al, 2014;Meinert et al, 2016;Ciaravella et al, 2019). Although G + 0.693-0.027 is not close to any obvious source of radiation, this cloud is embedded in an environment where the cosmic-ray ionization rate is enhanced by factors 100-1000 (Goto et al, 2013).…”

Characterizing Interstellar Medium, Planetary Surface and Deep Environments by Spectroscopic Techniques Using Unique Simulation Chambers at Centro de Astrobiologia (CAB)

“…Our ongoing collaboration with the Palermo Observatory in Italy and the National Central University in Taiwan is devoted to study the effect of X-rays emitted by young stars in the ice. These experiments were conducted in the ISAC setup using a Palermo home-made X-ray source, and later at the National Synchrotron of Taiwan (NSRRC) to increase the flux of soft X-rays [40,44,48,49,50,51,52,53,54,55]. Meanwhile, we employed swift heavy ions provided by the French accelerator GANIL at Caen to reproduce cosmic ray impact in the ice [56].…”