The Irradiation of Methyl Cyanide (CH3CN) Ice at 15 K with 200 keV

<p>Methyl cyanide (CH<sub>3</sub>CN) is the simplest of the organic nitriles found in space. It was first identified in the molecular clouds<strong>, </strong>Sagittarius Sgr A and Sgr B in 1971, through its emission lines in the vicinity of 2.7 mm from the <em>J</em> = 6 ® 5 transition. In 1974 it was also reported in comet Kohoutek. CH<sub>3</sub>CN, has since been detected in the Hale Bopp comet and, as of 2009, there are no less than 58 hot molecular core objects in which CH<sub>3</sub>CN had been found. Methyl cyanide has also been discovered beyond the Milky Way galaxy, in the NGC 253 galax, which lies in the local group of galaxies, some 10 million light-years from Earth<sup>[1]</sup>. It has also been detected in the interstellar medium (ISM) where it is thought to be made on the grain mantles.</p> <p>Upon irradiation of the Irradiation of methyl cyanide (CH<sub>3</sub>CN) ice at 15 K with 200 keV Protons, we observed several compounds. Although this experiment was conducted under different conditions than comparable ones carried out by other researchers (eg Hudson and Moore 2004; Hudson, Moore et al. 2008), similar results were obtained. The objectives were to determine which molecules would form upon irradiation of CH<sub>3</sub>CN ice. The astrophysical ice of CH<sub>3</sub>CN is present in the ISM, comets, solar bodies (<em>eg</em> Titan) and other galaxies. These places receive radiation fluxes from levels of only a few eV to in excess of MeV cm<sup>-2</sup> s<sup>-1</sup>, the result being that complex molecules are formed - <em>eg</em> HCN/CN<sup>-</sup>, HCCCN, H<sub>2</sub>C=C=NH and CH<sub>4</sub>. This experiment was carried out using 200 keV protons, and so replicated a particular radiation level similar to that present in space. It was discovered that, upon the irradiation of CH<sub>3</sub>CN under laboratory conditions, the same molecules as Hudson <em>et al </em>2004 were formed. These molecules may then play an important role in the wider astrobiological context. For instance, HCN is vital in the formation of nitrogenous compound.</p> <div><br /> <div> <p> </p> </div> </div> <p>Please insert your abstract HTML here.</p>

Photon and thermal processing of CH3NH2-bearing ices. Synthesis of prebiotic species at low temperature (such as formamide, ethylamine, and methylcyanide), and N-heterocycles during warm up.

<p>Hexamethylentetramine has drawn a lot of attention due to its potential to produce prebiotic species. This work aims to gain a better understanding in the chemical processes concerning methylamine under astrophysically relevant conditions. In particular, this work deeps into the formation of N-heterocycles in interstellar ice analogs exposed to UV radiation, which may lead to the formation of prebiotic species.</p> <p>Experimental simulations of interstellar ice analogs were carried out in ISAC. ISAC is an ultra-high vacuum chamber equipped with a cryostat, where gas and vapour species are frozen forming ice samples. Infrared and ultraviolet spectroscopy were used to monitor the solid phase, and quadrupole mass spectrometry served to measure the composition of the gas phase. The variety of species detected after UV irradiation of ices containing  methylamine revealed the presence of 12 species which have been already detected in the ISM, being 4 of them typically classified as complex organic molecules: formamide (HCONH<sub>2</sub>), methyl cyanide (CH<sub>3</sub>CN), CH<sub>3</sub>NH and CH<sub>3</sub>CHNH. Warming up of the irradiated CH<sub>3</sub>NH<sub>2</sub>-bearing ice samples lead to the formation of trimethylentriamine (TMT), a N-heterocycle precursor of HMT, and the subsequent synthesis of HMT at temperatures above 230 K.</p>

Rotational quenching of an interstellar gas thermometer: CH3CN⋯He collisions

Methyl cyanide serves as an interstellar gas thermometer. Image of its interaction potential with Helium.

Impact of nonconvergence and various approximations of the partition function on the molecular column densities in the interstellar medium

We emphasize that the completeness of the partition function, that is, the use of a converged partition function at the typical temperature range of the survey, is very important to decrease the uncertainty on this quantity and thus to derive reliable interstellar molecular densities. In that context, we show how the use of different approximations for the rovibrational partition function together with some interpolation and/or extrapolation procedures may affect the estimate of the interstellar molecular column density. For that purpose, we apply the partition function calculations to astronomical observations performed with the IRAM-30 m telescope towards the NGC 7538–IRS1 source of two N-bearing molecules: isocyanic acid (HNCO, a quasilinear molecule) and methyl cyanide (CH3CN, a symmetric top molecule). The case of methyl formate (HCOOCH3), which is an asymmetric top O-bearing molecule containing an internal rotor is also discussed. Our analysis shows that the use of different partition function approximations leads to relative differences in the resulting column densities in the range 9–43%. Thus, we expect this work to be relevant for surveys of sources with temperatures higher than 300 K and to observations in the infrared.

The ALMA-PILS survey: the first detection of doubly deuterated methyl formate (CHD2OCHO) in the ISM

Studies of deuterated isotopologues of complex organic molecules can provide important constraints on their origin in star formation regions. In particular, the abundances of deuterated species are very sensitive to the physical conditions in the environment where they form. Because the temperatures in star formation regions are low, these isotopologues are enhanced to significant levels, which enables the detection of multiply deuterated species. However, for complex organic species, so far only the multiply deuterated variants of methanol and methyl cyanide have been reported. The aim of this paper is to initiate the characterisation of multiply deuterated variants of complex organic species with the first detection of doubly deuterated methyl formate, CHD2OCHO. We use ALMA observations from the Protostellar Interferometric Line Survey (PILS) of the protostellar binary IRAS 16293–2422 in the spectral range of 329.1 GHz to 362.9 GHz. Spectra towards each of the two protostars are extracted and analysed using a local thermal equilibrium model in order to derive the abundances of methyl formate and its deuterated variants. We report the first detection of doubly deuterated methyl formate CHD2OCHO in the ISM. The D-to-H ratio (D/H ratio) of CHD2OCHO is found to be 2–3 times higher than the D/H ratio of CH2DOCHO for both sources, similar to the results for formaldehyde from the same dataset. The observations are compared to a gas-grain chemical network coupled to a dynamical physical model, tracing the evolution of a molecular cloud until the end of the Class 0 protostellar stage. The overall D/H ratio enhancements found in the observations are of about the same magnitude as the predictions from the model for the early stages of Class 0 protostars. However, that the D/H ratio of CHD2OCHO is higher than that of CH2DOCHO is still not predicted by the model. This suggests that a mechanism enhances the D/H ratio of singly and doubly deuterated methyl formate that is not in the model, for instance, mechanisms for H–D substitutions. This new detection provides an important constraint on the formation routes of methyl formate and outlines a path forward in terms of using these ratios to determine the formation of organic molecules through observations of differently deuterated isotopologues towards embedded protostars.