Ultraviolet radiation facilitates chemical reactions in interstellar ice mantles during star and planet formation. These chemical reactions produce interstellar complex organic molecules (iCOMs) that may be essential in the production of prebiotic molecules. The UV-driven chemistry in interstellar ices is studied with the Sublimation of Laboratory Ices Millimeter/submillimeter Experiment (SubLIME) technique, a laboratory setup that works at cryogenic conditions and ultra-high vacuum. Submillimeter rotational spectroscopy, quadrupole mass spectrometry, and Fourier-transform infrared transmission spectroscopy are used to monitor the products in both the solid and gas phases. A series of experiments were conducted to examine the impact of simultaneous UV photoprocessing and temperature programmed desorption (TPD) on simple interstellar ice analogs to simulate conditions more closely resembling the real conditions in dense molecular clouds or protoplanetary disks. Preliminary results indicate that the common assumption that equivalent UV fluences results in the same chemistry, regardless of total flux or duration, might be erroneous. Additional studies will further explore this chemistry in detail.

The formation of aminomethanol (), the predicted interstellar precursor to the simplest amino acid, glycine, is a fundamentally important process in prebiotic chemistry in the interstellar medium. A few studies have produced aminomethanol in mixed ices; Singh et al. were able to form aminomethanol in ices composed of methylamine and ozone, while Bossa et al. made aminomethanol in mixed ices made of formaldehyde (), ammonia (), and water () Singh, S. K.; Zhu, C.; La Jeunesse, J.; Fortenberry, R. C.; Kaiser, R. I. Nature Communications 2022, 13, 375. Bossa, J. B.; Theule, P.; Duvernay, F.; Chiavassa, T. The Astrophysical Journal 2009, 707, 1524–1532. However, aminomethanol has not yet been produced from ices with compositions that are realistic analogs of the simple composition of interstellar ices. We are therefore undertaking investigations of interstellar ice analogs composed of , , and CO in order to study this process. The SubLIME experiment will be utilized to conduct these studies. In this experimental setup the ices are processed via UV photolysis or temperature programmed desorption. Infrared spectroscopy is used to monitor the ice composition and determine the relative molecular abundance in deposited ices. A quadrupole mass spectrometer (QMS) serves to monitor the thermally desorbed gas phase species. Additionally, a mm/submm spectrometer is used to detect the gas phase species of ices once they have desorbed. These investigations elucidate the formation of this important molecule within an ice. Furthermore, spectra obtained can be compared to observational data. Here we report on the experimental design and initial results from these investigations.

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Singh, S. K.; Zhu, C.; La Jeunesse, J.; Fortenberry, R. C.; Kaiser, R. I. Nature Communications 2022, 13, 375.

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Recent experimental workNakai et al., Astrophys. J. 953, 162 (2023)onfirmed our 2011 predictionWoon, Astrophys. J. 728, 44 (2011)hat some cation-ice reactions are efficient at low temperature. Some workers have suggested, however, that cations may be neutralized by electrons expected to be present in ice before chemistry can occurRimola et al., Front. Astron. Space Sci. 8, 655405 (2021) The present work assesses the hypothesis that electrons can be trapped as anions in deep potential wells, allowing cation-ice reactions to occur. Clusters with 16-31H₂O molecules containing the hydroxide anion (OH⁻) were formed by various routes, including adding an electron to a cluster containing the hydroxyl radical (OH) or to a H atom loosely bound to the surface. When HCO⁺ is deposited on an (OH⁻)-nH₂O cluster, formic acid (HCOOH) forms, as found previously when OH⁻ is not present. The reaction introduces a proton into the cluster in the form the hydronium ion, H₃O⁺. The H₃O⁺ and OH⁻ entities are attracted to each other and often result in neutralization of the positive and negative charge via formation of H₂O. Vibrational spectra of clusters with OH⁻ will be shown.

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Nakai et al., Astrophys. J. 953, 162 (2023)c Woon, Astrophys. J. 728, 44 (2011)t Rimola et al., Front. Astron. Space Sci. 8, 655405 (2021).

The laboratory production of a molecule and measurements of its precise rest frequencies are essential to detect interstellar molecules in space. In this study, seven rotational transitions of the deuterated molecular ion SD⁺ have been measured in the 271–863 GHz region in the laboratory. This ion has been produced by DC-glow discharge using a mixture of D₂S and Argon in a free space cell under a temperature range of −140 to −160^°C. The rotational, centrifugal distortion, spin-spin interaction, spin-rotation, and hyper-fine constants have been determined; the standard deviation of the residuals in the fitting is 109 kHz. The measured frequencies can now be used for astronomical detection. We have investigated the line of SD⁺ toward the quasar PKS 1830-211 by using the ALMA archive. The z = 0.89 molecular absorber exits in front of this quasar and SH⁺ has been detected in the absorber [1,2]. There is a data set covering the 297 GHz region [3], which includes the N_J = 2₃–1₂ transition of SD⁺ at 561 GHz under redshift. A weak feature having an S/N of 2 is located at the same velocity with the peaks of SH⁺ and ³⁴SH⁺. The feature shows the column density of 3 ×10¹² cm⁻² using a dipole moment of 1.087 D [4] and assuming the excitation temperature of 5.14 K [1]. However, the column density provides an abundance ratio SD⁺/SH⁺ of 7%, which is overlarge considering the known deuterated species of ND (0.07−0.7%) and HDO (0.1%) [5]. Therefore, the present column density should be regarded as an upper limit of SD⁺. To detect this deuterated ion, the transitions that come from the lowest rotational level N_J = 0₁ are awaited to be investigated because of the low excitation temperature of this absorber. [1] S. Muller et al., A&A, 606, A109 (2017). [2] ALMA archive, 2017.1.00051. [3] ALMA archive, 2013.1.00020. [4] J. Senekowitsch et al., J. Chem. Phys., 83, 4661 (1985). [5] S. Muller et al., A&A, 637, A7 (2020).

This work follows our previous studies about the mono-deuterated (CH₃OCH₂D)Richard, C. ; et al., 2013, A& A 552, A117, 10.1051/0004-6361/201220826nd doubly deuterated (CH₃OCHD₂)Richard, C. ; et al., 2021, A& A 651, A120, 10.1051/0004-6361/202141282pecies of dimethyl ether. The analysis of their rotational spectra permitted their first detection in the Interstellar medium in the solar-type protostar IRAS 16293-2422. Dimethyl ether is one of the most abundant complex organic molecules in star- forming regions, and its D-to-H (D/H) ratios are important to understand its chemistry and trace the source history. Dimethyl ether is still a relatively light molecule compared to other COMs. Its spectrum is the most intense in the THz domain in the 100-150 K temperature regime.
The spectra were recorded in Lille from 150 to 1500 GHz using FLASH (Fast Lille Absorption emiSsion High resolution) spectrometer. It should be noted that the analysis here is quite different from that of the previous two species which exhibit internal rotation of a methyl rotor as if we have a deuterium atom in each methyl group. Here we have 4 equivalent conformers, multiplets could be observed due to tuneling effects between equivalent configurations.The analysis of the spectra was carried out using the RAS formalism implemented in the SPFIT code. The spectroscopic results and its search in ISM will be presented.
This work was supported by the Programme National "Physique et Chimie du Milieu Interstellaire" (PCMI) of CNRS-INSU with INC-INP co-funded by CEA and CNES

Isotopic fractionation is a set of chemical processes that distributes less abundant isotopes into molecules (e.g. D substitutes H). Deuterium fractionation is one of the best tools to follow the evolution of material across star and planet formationCeccarelli, C.; Caselli, P.; Bockelée-Morvan, D; et al. 2014. Protostars and Planets VI, Henrik Beuther, Ralf S. Klessen, Cornelis P. Dullemond, and Thomas Henning (eds.), University of Arizona Press, Tucson, p.859-882 For example, the inheritance of water from pre-stellar cores to planets has been shown via observations and modelling of water deuteration in star-forming regionsCleeves, L. I. ; Bergin, E. A.; et al. Science, Volume 345, Issue 6204, pp. 1590-1593 (2014) Water is inherited efficiently in the form of ice. Thick ice layers build up right before the protostar forms, and together with water, other molecules also freeze out and can be potentially inherited in later stages of star formation, as well as in forming planets. To assess what else is inherited together with water, and determine the level of molecular complexity that is available to forming planets, a systematic and comprehensive survey of deuterated molecules in star-forming regions is necessary. Unfortunately, the laboratory spectroscopy of deuterated isotopologues of abundant insterstellar molecules is far from complete, especially in the case of complex organic molecules (COMs). The Center for Astrochemical Studies (CAS) laboratories at the Max Planck Institute for Extraterrestrial Physics started a systematic study of deuterated COMs with a multidisciplinary approach that involves laboratory spectroscopy, radioastronomical observations, and chemical modelling. In my talk, I will present our projects, discuss the challenges of this work, and report on recent results (e.g. the first interstellar detection of doubly deuterated acetaldehydeFerrer Asensio, J.; Spezzano, S.; Coudert, L.; et al. 2023. Astronomy & Astrophysics, Volume 670, A177. Ceccarelli, C.; Caselli, P.; Bockelée-Morvan, D; et al. 2014. Protostars and Planets VI, Henrik Beuther, Ralf S. Klessen, Cornelis P. Dullemond, and Thomas Henning (eds.), University of Arizona Press, Tucson, p.859-882. Cleeves, L. I. ; Bergin, E. A.; et al. Science, Volume 345, Issue 6204, pp. 1590-1593 (2014) . Ferrer Asensio, J.; Spezzano, S.; Coudert, L.; et al. 2023. Astronomy & Astrophysics, Volume 670, A177)

Methanol is the most abundant saturated-organic molecule and is known as an important species to form more complex organic molecules in interstellar clouds. However, deriving the actual abundances of methanol often suffers not only from the high opacity of the lines but also from the insufficiency of spectroscopic information. It is especially true for methanol isotopologues: the rotation transition of methanol significantly suffers from the uncertainty of intrinsic line intensities (Sμ²) due to the floppy nature of this species. Although it is a critical parameter to derive accurate column density and temperature of the molecular gas, they are not straightforward to be evaluated theoretically, especially for the asymmetric-top asymmetric-frame isotopologue. By considering the importance of studying isotopic fractionation in methanol, we have developed an emission-type spectrometer, SUMIRE, using techniques developed for ALMA to determine line intensities and transition frequency of such species. Based on the laboratory measurement of line intensities, we first examined astronomical impacts on methanol deuteration. In this presentation, we will introduce application of our results on methanol deuteration study in the disk around an eruptive young star V883 Ori by utilizing ALMA Band 6 line survey. Deuterium fractionation, which refers to the enhancement of the D to H ratio in comparison to its elemental abundance, is a valuable tool for studying the physical and chemical characteristics of interstellar sources. Methanol is one of the molecules that exhibit significant deuterium enhancement, and its deuteration pathway has been extensively studied. It is postulated that mono-deuterated methanol, in particular, forms efficiently on grain surfaces prior to the onset of star formation. As a result, the D to H ratio is commonly used to probe history of the physical conditions in different astronomical sources. However, the ratio between CH₂DOH and CH₃OD often deviates from the expected value of 1 (or 3 if we consider the statistical weight) and even varies significantly depending on sources. Our study demonstrates the impact of precise spectroscopic data on determining the abundance of CH₂DOH, contributing to a better understanding of the methanol deuteration process. It would also help understanding the origin of high deuteration of water known in the solar system

In this study, we continue our discussion from last year on laboratory investigations of carbon-sulfur compounds. These compounds form a significant part of the chemical makeup found in interstellar gas and dust, making their laboratory characterization highly relevant to the astrochemical community. This year, our focus is on the spectroscopic characterization of the millimeter and submillimeter rotational spectra of two molecular species observed in space: deuterated thioformaldehyde (D₂CS) and the higher energy isomeric form of protonated OCS (HOCS⁺).
Deuterated thioformaldehyde is a well-known molecule, abundant and widespread in the interstellar medium. In this work we will show our recent extension of its laboratory rotational spectrum into the sub-THz range, accompanied by high-level coupled cluster quantum chemical calculations of the global [D₂,C,S] system.Inostroza-Pino, N., et al., Molecular Physics e2280762 (2023) Protonated OCS has been recently detected in the interstellar medium towards the G+0.693-0.027 molecular cloud in the Galactic CentreSanz-Novo, M., et al., arXiv:2402.15405 (2024) in its HOCS⁺ form, despite being  ∼  5kcal/mol ( ∼  2500K) higher in energy than the HSCO⁺ isomeric form, still undetected in space. Motivated by this new observational study we have investigated and detected the millimeter rotational spectrum of HOCS+, and we will present here the main laboratory details along with the outcomes of our analysis.

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Footnotes:

Inostroza-Pino, N., et al., Molecular Physics e2280762 (2023)
Sanz-Novo, M., et al., arXiv:2402.15405 (2024),

Basis of Research: Recently, Berné et al. (2023) published a paper on a JWST emission spectrum, which they assigned to CH₃+. For example, they assigned the strong emission lines from the 7.1752 μm to 7.1622 μm as the Q branch lines of the ν₂ fundamental band of CH₃+.
Assignment using the NIST Database: These spectral lines are readily assigned as due to atomic emission lines based on the NIST atomic spectrum database. For example, the line at 7.1752 μm is due to Magnesium and the 7.1622 μm is due to Nitrogen 4+.
Conclusion of Research: The JWST spectrum is not due to CH₃+. Molecular infrared emission is very weak. It is observable only from planets but not from interstellar space.
*Berné, O. and 57 authors, 2023, Nature accelerated article preview.

Complex organic molecules (COMs) are observed in every stage of star formation from molecular clouds to the formation of protoplanetary disks. Many of these molecules are formed via energetic processing of icy grain mantles, while more complex chemical processing occurs in the gas phase at the hot core or hot corino stage. We are surveying a set of 30 star-forming regions to examine the relationship between COMs and the physical properties of the cores. In this study, we observed the hot corino NGC 1333 IRAS 4B with the Northern Extended Millimeter Array (NOEMA). The two cores of IRAS 4B are imaged in the 145 GHz spectral region, revealing the spatial distribution of various COMs. Multiple regions of extended emission are observed, indicating outflows from both cores. We will present the initial imaging results, molecular detections, and spectral analysis of these observations. We will discuss the results in the context of COM formation in the early stages of star and planet formation.

Studying molecular complexity in the early stages of star formation is crucial to further our understanding of the formation pathways of planetary systems. We previously characterized the neighboring star-forming cores W3(H₂O) and W3(OH), revealing extended emission from the cores that trace bipolar outflows. While the original study focused on imaging the molecular inventory in these cores, the current work focuses on characterizing these outflows. Using NOEMA interferometric observations of the cores, molecular spectra were extracted from the datacubes and molecular inventory identified in the outflows. The Global Optimization and Broadband Analysis Software for Interstellar Chemistry (GOBASIC) developed by previous members of the Widicus Weaver Group was used to conduct spectral analysis. By running GOBASIC using the previously obtained NOEMA observations of the cores and fitting molecular spectra known to exist in the cores within the outflow regions, we can compare the chemical composition of the W3 cores to their outflows. By comparing the W3 cores and their outflows, we can better understand the formation processes of prebiotic molecules and planetary systems, and the evolutionary processes of star-forming regions.

Basis of Research: We attempt to observe infrared spectrum of H₂O in the Central Molecular Zone (CMZ) of the Galactic center (GC) toward 10 stars which were used for observations of H₃⁺, Oka et al. (2019)^a

Theoretical Spectrum: The spectrum is predicted to be in absorption in diffuse clouds at the wavenumbers reported by Mecke (1933)^b at 3198.9 cm$^{-1}$ corresponding to the 1₁₁ <- 0 transition of para-H₂O and at 3215.2 cm^-1 corresponding to the 2₁₂ <- 1₀₁ transition of ortho-H₂O. This extremely simple rotational structure is due to the very rapid rotational spontaneous emission of H₂O.

Para- versus ortho-: If the chemistry in the CMZ is thermodynamic, all H₂O will be in the lowest 0₀₀ para level. It is interesting to see the observed ratio of para and ortho and its variation depending on the location of stars.

^aOka, T. Geballe, T.R., Goto, M., Usuda, T., McCall, B.J., Indriolo, N. 2019, Astrophys. J. 883:545 (31pp)

^bMecke, R. 1933, Z. Phys. 81, 313-331