Carbamic acid produced by the UV/EUV irradiation of interstellar ice analogs

Abstract

Context. Carbamic acid (NH 2 COOH) is the smallest amino acid, smaller than the smallest proteinaceous amino acid glycine. This compound has never been observed in the interstellar medium (ISM). Previous experiments where ice mixtures containing H 2 O, CO 2 and NH 3 were subjected to 1-MeV proton bombardment showed that carbamic acid is formed in a stable zwitterionic (NHAims. In the present work, we have carried out irradiations of ice mixtures containing H 2 O, 12 CO 2 / 13 CO 2 and NH 3 with ultraviolet (UV)/extreme ultraviolet (EUV) photons provided by a synchrotron source in the 4-20 eV range, and compared the results with those obtained for energetic protons. Methods. Infrared (IR) spectroscopy and mass spectrometry were used to identify the formed photo-products and monitor their evolution in the ices at 15 K and during the warming up to room temperature in the formed residues. Results. We identified the IR absorption features of HNCO, OCN − , CO, NH + 4 and NH 2 CHO at low temperature in the ices, and features assigned to carbamic acid in the residues around 250 K. Finally, we conclude that under our experimental conditions, unlike what was obtained after bombardment with energetic protons, carbamic acid may be formed in the neutral form, and propose some photochemical pathways leading to its formation.

Carbamic acid and carbamate formation in NH$_{\sf 3}$:CO$_{\sf 2}$ ices – UV irradiation versus thermal processes

“…A confirmation of the detection of these molecules and the ratio C/D could be provided by the Rosetta mission devoted to analyze the comet nucleus. Our results also provide fresh insight that improves the study performed by Chen et al (2007). In particular for the carbamic acid formation at 250 K. In this study, they irradiated at 15 K with UV/EUV photons, ice mixtures ( 12 CO 2 :H 2 O, NH 3 : 12 CO 2 :H 2 O, NH 3 : 13 CO 2 :H 2 O) followed by warming to 250 K. Chen et al (2007) proposed that carbamic acid could be formed from a thermal reaction between H 2 O and HNCO, photoproducts which were observed after irradiation.…”

“…Our results also provide fresh insight that improves the study performed by Chen et al (2007). In particular for the carbamic acid formation at 250 K. In this study, they irradiated at 15 K with UV/EUV photons, ice mixtures ( 12 CO 2 :H 2 O, NH 3 : 12 CO 2 :H 2 O, NH 3 : 13 CO 2 :H 2 O) followed by warming to 250 K. Chen et al (2007) proposed that carbamic acid could be formed from a thermal reaction between H 2 O and HNCO, photoproducts which were observed after irradiation. On the basis of their spectra, HNCO is formed in such low quantity (absorbance of 0.02 or less) that it is unlikely to be the origin of carbamic acid that they observed at 250 K. As demonstrated previously Raunier et al (2003), the thermal reaction between HNCO and H 2 O produces [H 3 O + ][OCN − ] at temperatures higher than 130 K. We propose that the products they observed at 250 K were produced mainly by thermal reaction between the residual NH 3 and CO 2 .…”

“…At 250 K, the remaining organic residue was assigned to carbamic acid in its zwitterionic form NH 3 + COO − . Chen et al (2007) performed irradiation of NH 3 :CO 2 :H 2 O ice mixtures at 15 K with UV/EUV photons of 4-20 eV (310-62 nm), and followed the reaction by IR and mass spectroscopy, while warming the ice films to 250 K. Along with the IR features HNCO, OCN − , NH 4 + , CO and NH 2 (CO)H, they identified carbamic acid in its neutral form. It is important to note that in every study, carbamic acid was identified after both irradiation and heating to 250 K. We will show that heating to 250 K after irradiation at low temperature has for effect to allow the reactants that have not been decomposed by irradiation to thermally react.…”

Soft X-Ray Irradiation of Methanol Ice: Formation of Products as a Function of Photon Energy

“…The experiments have been performed with the Interstellar Photoprocess System (IPS; Chen et al 2007). The IPS is an ultrahigh vacuum (UHV) chamber of typical pressure 1-3 × 10 −10 mbar.…”

TGA–FT-IR study of pyrolysis of poly(hydrogen cyanide) synthesized from thermal decomposition of formamide. Implications in cometary emissions

“…From an interstellar chemistry point of view, carbamic acid and ammonium carbamate are readily produced from the ice mantle of a typical interstellar grain and should therefore be a detectable species in molecular clouds [24,25]. Carbamic acid can be considered the simplest amino acid, even simpler than glycine.…”