Snow lines, the boundaries where the most abundant volatiles such as H₂O, CO₂ and CO freeze out from the gas phase onto dust grains in the midplane of protoplanetary disks, are believed to play an important role in planet formation and composition. Locating the CO snow line is challenging in disks. This has prompted an exploration of chemical signatures of CO freeze-out and desorption. We present ALMA observations of the CO, N₂H⁺ and DCO⁺ emission to probe the CO freeze-out and desorption in protoplanetary disks, and evaluate their utility as tracers of the CO snow line location.

Sulfur is a chemical element that enjoys one of the highest cosmic abundances. However, it has traditionally played a relatively minor role in the field of astrochemistry, being drowned out by other chemistries after it depletes from the gas phase during the transition from a diffuse cloud to a dense one. A wealth of laboratory studies have provided clues to its rich chemistry in the condensed phase, and most recently, a report by a team behind the Rosetta spacecraft has significantly helped to unveil its rich cometary chemistry. We have set forth to use this information to greatly update/extend the sulfur reactions within the OSU gas/grain astrochemical network in a systematic way, to provide more realistic chemical models of sulfur for a variety of interstellar environments. We present here some results and implications of these models.

Cosmic rays are a form of high energy radiation found throughout the galaxy that can cause significant physio-chemical changes in solids, such as interstellar dust grain ice-mantles. These particles consist mostly of protons and can initiate a solid-state irradiation chemistry of significant astrochemical interest. In order to better understand the chemical effects of long-term exposure to ionizing radiation, we have written a new Monte Carlo model, CIRIS: the Chemistry of Ionizing Radiation in Solids, which is, to the best of our knowledge, the first successful program of its kind to follow the damage and subsequent chemistry of an irradiated material over time. In our code, two distinct regimes are considered. One is dominated by the atomic physics of track calculations in which both the irradiating proton and the subsequently generated secondary electrons are followed on a collision by collision basis. The other regime occurs after the ion-target collision, in which mobile species are free to randomly hop throughout the bulk of the ice and react via a diffusive mechanism. Here, we will present an initial test of our code in which we have successfully modeled previous experimental work. In these simulations, we are able to reproduce the measured abundances and predict the approximate ice thickness used in that study.

Thanks to the new spectroscopic windows opened by the recent generation of telescopes, a large number of molecular lines have been detected. In particular, nuclear-spin astrochemistry has gained interest owing to numerous ortho-to-para ratio (OPR) measurements for species including H₃⁺, CH₂, C₃H₂, H₂O, NH₃, NH₂, H₂S, H₂CS, H₂O⁺ and H₂Cl⁺. Any multi-hydrogenated species can indeed present different spin configurations, if some of their hydrogen nuclei are identical, and the species thus exist in distinguishable forms, such as ortho and para. In thermal equilibrium, OPRs are only functions of the temperature and since spontaneous conversion between ortho and para states is extremely slow in comparison with typical molecular cloud lifetimes, OPRs were commonly believed to reflect a "formation temperature". However, observed OPRs are not always consistent with their thermal equilibrium values, as for the NH₃ and NH₂ cases. It is thus crucial to understand how interstellar OPRs are formed to constrain the information such new probes can provide. This involves a comprehensive analysis of the processes governing the interstellar nuclear-spin chemistry, including the formation and possible conversions of the different spin symmetries both in the gas and solid phases. If well understood, OPRs might afford new powerful astrophysical diagnostics on the chemical and physical conditions of their environments, and in particular could trace their thermal history. In this context, observations of non-thermal values for the OPR of the radical NH₂ toward four high-mass star-forming regionsPersson et al. 2016, A&A, 586, A128 and a 3:1 value measured for the H₂Cl⁺ OPR toward diffuseNeufeld et al. 2016, ApJ, 807, 54nd denser gas, led us to develop detailed studies of the mechanisms involved in obtaining such OPRs with the aid of quasi-classical trajectory calculationsLe Gal et al. 2016, A&A, 596, A35 and Le Gal et al., in prep We will present these new promising results, improving our understanding of the interstellar medium.

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Persson et al. 2016, A&A, 586, A128, Neufeld et al. 2016, ApJ, 807, 54a Le Gal et al. 2016, A&A, 596, A35 and Le Gal et al., in prep.

The Center for Astrochemical Studies at the Max Planck Institute for Extraterrestrial Physics in Garching, is a recently established group which collects scientists with very diverse backgrounds. In the same group observers, theoreticians, chemists and molecular astrophysicists join their efforts with the ultimate goal of properly interpreting observations with the new generation telescopes and unveiling our astrochemical/physical heritage. Among these tasks, the gas-phase spectroscopic characterisation of molecular species of astrophysical relevance is one of the main goals of the laboratory sub-group. This talk will mainly focus on the first experiment built in our center, the CASAC (CAS Absorption Cell) spectrometer: this experiment has been optimised on the production and probe of small molecular ions and radicals. The main laboratory techniques along with the more prominent outcomes of recent studies will be presented. Finally, a brief update on the status of the other instruments available in our center will be given, including their planned upgrades.

Cold dark clouds represent a very unique environment to test our knowledge of the chemical and physical evolution of the structures that ultimately led to life. Starless cores, such as L183, are indeed the first phase of the star formation process and the nursery of chemical complexity. In this work we present the detection of several large astronomical molecules in the prestellar core L183, as a result of a 3mm single-pointing survey performed with the IRAM 30m antenna. The abundances of the observed species will be then compared to those found in similar environments, highlighting correspondences and uniquenesses of the different sources.

Methyl formate CH₃OC(O)H is a relatively abundant component of the interstellar medium (ISM) E. Chruchwell, G. Winnewisser, A&A, 45, 229 (1975) Thus, we decided to study its sulfur derivatives as they can be reasonably proposed for detection in the ISM. In fact there is two relatively stable isomers for methyl thioformate, S-Methyl thioformate CH₃SC(O)H and O-Methyl thiofomate CH₃OC(S)H. Theoretical investigations on these molecules have been done recently by Senent et al.M. L. Senent, C. Puzzarini, M. Hochlaf, R. Dominguez-Gomez, and M. Carvajal, J. Chem. Phys., 141, 104303 (2014) Previous experimental investigations were performed only for the S-Methyl thioformate in the 10-41 GHz spectral range by Jones et al.G. I. L. Jones, D. G. Lister, N. L. Owen, J. Mol. Spectrosc., 60, 348 (1976)nd Caminati et al.W. Caminati, B. P. V. Eijck, D. G. Lister, J. Mol. Spectrosc., 90, 15 (1981) For the present study both isomers were synthesized and the millimeter wave spectrum was then recorded for the first time from 150 to 660 GHz with the Lille’s spectrometer based on solid-state sources. The internal rotation effect on the millimeter wave spectra is not the same for these two molecules because the barrier height to internal rotation is relatively low for the S- isomer (V₃ ≈ 140 cm⁻¹) and rather high for the O- isomer (V₃ ≈ 700 cm⁻¹). Analysis of the ground and excited torsional states performed with the BELGI-C_s codeJ. T. Hougen, I. Kleiner, and M. Godefroid, J. Mol. Spectrosc. 163, 559 (1994)ill be presented and discussed. We will provide the search for methyl thioformate in different sources.

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Footnotes:

E. Chruchwell, G. Winnewisser, A&A, 45, 229 (1975). M. L. Senent, C. Puzzarini, M. Hochlaf, R. Dominguez-Gomez, and M. Carvajal, J. Chem. Phys., 141, 104303 (2014). G. I. L. Jones, D. G. Lister, N. L. Owen, J. Mol. Spectrosc., 60, 348 (1976)a W. Caminati, B. P. V. Eijck, D. G. Lister, J. Mol. Spectrosc., 90, 15 (1981). J. T. Hougen, I. Kleiner, and M. Godefroid, J. Mol. Spectrosc. 163, 559 (1994)w

Cyclopropenylidene, c-C₃H₂, is one of the more abundant organic molecules in the interstellar medium, as evidenced from astronomical detection of its single ¹³C and both its singly- and doubly-deuterated isotopic species. For this reason, vibrational satellites are of considerable astronomical interest, and were the primary motivation for the earlier laboratory work by Mollaaghababa and co-workers [1].
The recent detection of intense unidentified lines near 18 GHz in a hydrocarbon discharge by FT microwave spectroscopy has spurred a renewed search for the vibrational satellite transitions of c-C₃H₂. Several strong lines have been definitively assigned to the v₆ progression on the basis of follow-up measurements at 3 mm, double resonance and millimeter-wave absorption spectroscopy, and new theoretical calculations using a rovibrational VMP2 method [2] and a high-quality ab initio potential energy surface. The treatment was applied to several excited states as well as the ground state, and included deperturbation of Coriolis interactions. [1] R. Mollaaghababa, C.A. Gottlieb, J. M. Vrtilek, and P. Thaddeus, J. Chem. Phys., 99, 890-896 (1992). [2] P. B. Changala and J. H. Baraban. J. Chem. Phys., 145, 174106 (2016).

The knowledge of synthetic routes of complex organic molecules is still far to be fully understood. The creation of reliable models is particularly challenging. Hollis et al.Hollis, J. M.; et al., 2006, ApJ 642, 933ointed out that the observations of molecular isomers provides an excellent tool to evaluate the hypothesis of the synthetic pathways. In the group of isomers C₃H₄O that contains two unsaturations, the three most stable are cyclopropanone, propenal (also known as acrolein) and methyl ketene. Among these isomers, only propenal was tentatively detected in Sgr B2(N)Hollis, J. M.; et al., 2006, ApJ 643, L25 Spectroscopic measurements of methyl ketene CH₃CHCO are limited to the microwave domainBak, B.; et al., 1966, J. Chez. Phys. 45, 883 We extended the measurements into millimeter waves in order to provide accurate frequency predictions suitable for astrophysical purposes. Methyl ketene has one more carbon atom than acetaldehyde (CH₃CHO) and in terms of rotational spectroscopy is quite similar to acetaldehyde. The analysis of the rotational spectrum of methyl ketene is complicated due to internal rotation of the methyl group, that is characterized by the barrier of intermediate height V₃ = 416 cm⁻¹, and by quite large value of the coupling parameter ρ = 0.194. The spectroscopic results and the searches of methyl ketene in Orion will be presented.
This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under ANR-13-BS05-0008-02 IMOLABS

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Footnotes:

Hollis, J. M.; et al., 2006, ApJ 642, 933p Hollis, J. M.; et al., 2006, ApJ 643, L25. Bak, B.; et al., 1966, J. Chez. Phys. 45, 883.

Isomers of H₂C_2n+1O are examples of complex organic molecules that are either known or proposed to exist in the interstellar medium. For the smallest of these chains (H₂C₃O) only two of three isomers are observed in space: propynal (HC(O)CCH) and cyclopropenone (c−C₃H₂O), while evidence for the remaining isomer propadienone (H₂C₃O) is currently lacking. Potentially, this behaviour may be rationalised by a thermodynamic argument: several studies have provided quantum chemical calculations in an effort to determine the relative thermodynamic stability between these three isomers. An early study by Radom, at the SCF/6-31G** level ranked HC(O)CCH as the thermodynamic minimum, followed by H₂C₃O, and c−C₃H₂O. The most recent determination by Karton and Talbi, using W2-F12 theory, places H₂C₃O as the lowest energy isomer; 2.5 kJ mol⁻¹ lower than the HC(O)CCH form. In an attempt to resolve this long-standing ambiguity, we were motivated to provide high level calculations based on the HEAT protocol. In this talk, we will discuss the relative stability of H₂C₃O and H₂C₅O isomers, along with their sulfur analogues, as revealed by HEAT345(Q) theory.