Molecular Distributions of the Disk/Envelope System of L483: Principal Component Analysis for the Image Cube Data

Unbiased understanding of molecular distributions in a disk/envelope system of a low-mass protostellar source is crucial for investigating physical and chemical evolution processes. We have observed 23 molecular lines toward the Class 0 protostellar source L483 with ALMA and have performed principal component analysis (PCA) for their cube data (PCA-3D) to characterize their distributions and velocity structures in the vicinity of the protostar. The sum of the contributions of the first three components is 63.1%. Most oxygen-bearing complex organic molecule lines have a large correlation with the first principal component (PC1), representing the overall structure of the disk/envelope system around the protostar. Contrary, the C18O and SiO emissions show small and negative correlations with PC1. The NH2CHO lines stand out conspicuously at the second principal component (PC2), revealing more compact distribution. The HNCO lines and the high-excitation line of CH3OH have a similar trend for PC2 to NH2CHO. On the other hand, C18O is well correlated with the third principal component (PC3). Thus, PCA-3D enables us to elucidate the similarities and the differences of the distributions and the velocity structures among molecular lines simultaneously, so that the chemical differentiation between the oxygen-bearing complex organic molecules and the nitrogen-bearing ones is revealed in this source. We have also conducted PCA for the moment 0 maps (PCA-2D) and that for the spectral line profiles (PCA-1D). While they can extract part of characteristics of the molecular line data, PCA-3D is essential for comprehensive understandings. Characteristic features of the molecular line distributions are discussed on NH2CHO.

The quest of chirality in the interstellar medium

Context. All but one complex organic molecule (COM) detected so far in the interstellar medium (ISM) are achiral; propylene oxide (c-C2H3O)-CH3 is the only exception to this. Finding other chiral species is a priority for astrobiology to progress in the understanding of the emergence of life. Whatever the conditions of their formation, i.e., gas phase or grain chemistry, the detection relies on rotational spectra. This means that, if adsorbed after formation in the gas phase or directly formed on the icy grains, these COMs must escape in the gas phase as free flyers to be detectable. Aims. Learning the lesson drawn from the only observation of a chiral compound and considering the structural constraints imposed to a molecule to be chiral, we look at what species could satisfy these conditions and be potential targets for a radio astronomy search in the ISM gas phase. Methods. This question was addressed by combining two complementary approaches that rely on density functional theory. The structure, energetics, and spectroscopic parameters of each potential candidate were determined using molecular calculations. The propensity for a molecule to remain trapped on the ice coating of the grains was evaluated by numerical simulations making use of a solid state periodic model. Results. Replacing the -CH3 group on rigid propylene oxide by -CN, -CCH, -NH2, -OH, or -HCO gives oxirane daughter molecules whose adsorption energies divide into two classes: below and above the adsorption energy of H2O on solid water-ice ~13.5 kcal mol−1. Conclusions. The best chiral candidate would be a rigid molecule for an easier determination of its radio spectra. This molecule would be composed of a central carbon linked to one hydrogen and three different chemical groups as simple as possible. If not the most stable isomer, this candidate should be as close as possible on the energy scale, possess a significant dipole moment, and be less strongly attached to the ice than H2O itself.

Infra-Red Assisted Synthesis of Prebiotic Glycine

<p>In the present study, we have shown for the first time how glycine can be synthesized under prebiotic-like conditions using an Infra-Red laser to trigger the reaction. In particular, we observed that in the low-density conditions it can be obtained from simple ion-molecule reactions of acetic acid and protonated hydroxylamine. This reaction, studied years ago in more dense conditions [<i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 9910-9917R], was the center of a controversy, since accurate quantum chemistry calculations have shown that it is not barrierless [<i>Astrophys. J.</i> <b>2012</b>, <i>748</i>, 99] such that a source of energy is needed. In space, and more in general in prebiotic conditions (interstellar medium, comets, asteroids) temperature is very low but the photon density can be important. Here we propose a way of synthesizing such complex organic molecule in a very low-pressure environment (about 10^-3 mbar). This way of forming complex organic molecule is of relevance also beyond the prebiotic interest of finding a scenario which was at the origin of the synthesis of such molecules. In fact our work proposes a new way of assisting reactions using IR radiation. Only few cases were found in which IR can trigger complex reactions (i.e. not simple dissociations) while there is a clear interest of using such low-energy radiation. This study will be at the basis of new researches devoted to find other reactions which can be assisted by IR laser.</p>

Infra-Red Assisted Synthesis of Prebiotic Glycine

<p>In the present study, we have shown for the first time how glycine can be synthesized under prebiotic-like conditions using an Infra-Red laser to trigger the reaction. In particular, we observed that in the low-density conditions it can be obtained from simple ion-molecule reactions of acetic acid and protonated hydroxylamine. This reaction, studied years ago in more dense conditions [<i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 9910-9917R], was the center of a controversy, since accurate quantum chemistry calculations have shown that it is not barrierless [<i>Astrophys. J.</i> <b>2012</b>, <i>748</i>, 99] such that a source of energy is needed. In space, and more in general in prebiotic conditions (interstellar medium, comets, asteroids) temperature is very low but the photon density can be important. Here we propose a way of synthesizing such complex organic molecule in a very low-pressure environment (about 10^-3 mbar). This way of forming complex organic molecule is of relevance also beyond the prebiotic interest of finding a scenario which was at the origin of the synthesis of such molecules. In fact our work proposes a new way of assisting reactions using IR radiation. Only few cases were found in which IR can trigger complex reactions (i.e. not simple dissociations) while there is a clear interest of using such low-energy radiation. This study will be at the basis of new researches devoted to find other reactions which can be assisted by IR laser.</p>

Astrophysical detections and databases for the mono deuterated species of acetaldehyde CH2DCOH and CH3COD

Context. Detection of deuterated species may provide information on the evolving chemistry in the earliest phases of star-forming regions. For molecules with two isomeric forms of the same isotopic variant, gas-phase and solid-state formation pathways can be differentiated using their abundance ratio. Aims. Spectroscopic databases for astrophysical purposes are built for the two mono deuterated isomeric species CH2DCOH and CH3COD of the complex organic molecule acetaldehyde. These databases can be used to search and detect these two species in astrophysical surveys, retrieving their column density and therefore abundances. Methods. Submillimeter wave and terahertz transitions were measured for mono deuterated acetaldehyde CH2DCOH which is a non-rigid species displaying internal rotation of its asymmetrical CH2D methyl group. An analysis of a dataset consisting of previously measured microwave data and the newly measured transition was carried out with a model accounting for the large amplitude torsion. Results. The frequencies of 2556 transitions are reproduced with a unitless standard deviation of 2.3 yielding various spectroscopic constants. Spectroscopic databases for astrophysical purposes were built for CH2DCOH using the results of the present analysis and for CH3COD using the results of a previous spectroscopic investigation. These two species were both searched for and are detected toward a low-mass star-forming region. Conclusions. We report the first detection of CH2DCOH (93 transitions) and the detection of CH3COD (43 transitions) species in source B of the IRAS 16293−2422 young stellar binary system located in the ρ Ophiuchus cloud region, using the publicly available ALMA Protostellar Interferometric Line Survey.

Questions about the evolution of ices, from diffuse molecular clouds to comets

The surfaces of interstellar and circumstellar dust grains are the sites of molecule formation, most of which, except H2, stick and form ice mantles. The study of ice evolution thus seems directly relevant for understanding our own origins, although the relation between interstellar and solar system ices remains a key question. The comparison of interstellar and solar system ices relies evidently on an accurate understanding of the composition and processes in both environments. With the accurate in situ measurements available for the comet 67P/Churyumov-Gerasimenko with the Rosetta mission, improving our understanding of interstellar ices is the more important. Here, I will address three specific questions. First, while laboratory experiments have made much progress in understanding complex organic molecule (COM) formation in the ices, the question remains, how does COM formation depend on environment and time? Second, what is the carrier of sulfur in the ices? And third, can ice absorption bands trace the processing history of the ices? Laboratory experiments, ranging from infrared spectroscopy to identify interstellar ice species, to surface experiments to determine reaction parameters in ice formation scenarios, to heating and irradiation experiments to simulate space environments, are essential to address these questions and analyze the flood of new observational data that will become available with new facilities in the next 2-10 years.

A variable-temperature X-ray diffraction and theoretical study of conformational polymorphism in a complex organic molecule (DTC)

A small conformational change in the asymmetric unit has a significant effect on how non-covalent interactions determine (i) the crystal packing and (ii) the effect of T on the relative balance of electrostatics and dispersion–repulsions.