Methanol is an abundant and widespread molecule in the interstellar medium. Its opacity in star forming regions is frequently so high that transitions of CH₃¹⁸OH are employed to characterize the abundance and excitation of CH₃OH.e.g., H. S. P. Müller et al., Astron. Astrophys. 587 (2016) A92, J. K. Jørgensen et al., Astron. Astrophys. 595 (2016) A117.t appeared thus plausible that CH₃¹⁷OH is detectable in the ISM. Therefore, we are investigating the rotational spectrum of CH₃¹⁷OH up to 1.1 THz employing a methanol sample with 20% ¹⁷O.The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via the collaborative research centers SFB 956, project area B3, and SFB 1601, project area A4 and Inf, and through the Gerätezentrum "Cologne Center for Terahertz Spectroscopy". The work in Kharkiv was supported by the Volkswagen Stiftung. The assistance of the Science and Technology Center in the Ukraine is acknowledged (STCU partner project P756).he ¹⁷O quadrupole splitting is usually quite well resolved at low values of J. Even though the initial data set was very limited,Y. Hoshino et al., J. Mol. Spectrosc. 148 (1991 506.nitial assignments were fairly straightforward. At the current stage of the analysis we limit ourselves mainly to transitions within v_t ≤ 1. The analysis is carried out applying the rho axis method and the RAM36hf program code.R. Motiyenko et al., J. Mol. Struct. 1213 (2020) 128037.e will present the results of our laboratory study and those of searches for this isotopolog toward Sagittarius B2(N).

---

Footnotes:

e.g., H. S. P. Müller et al., Astron. Astrophys. 587 (2016) A92, J. K. Jørgensen et al., Astron. Astrophys. 595 (2016) A117.I The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via the collaborative research centers SFB 956, project area B3, and SFB 1601, project area A4 and Inf, and through the Gerätezentrum "Cologne Center for Terahertz Spectroscopy". The work in Kharkiv was supported by the Volkswagen Stiftung. The assistance of the Science and Technology Center in the Ukraine is acknowledged (STCU partner project P756).T Y. Hoshino et al., J. Mol. Spectrosc. 148 (1991 506.i R. Motiyenko et al., J. Mol. Struct. 1213 (2020) 128037.W

We have investigated the rotational spectrum of isobutene recently in the millimeter and submillimeter regions and detected it subsequently in the chemically rich molecular cloud G+0.693-0.027.M. Fatima et al., Astron. Astrophys. 680 (2023) A25.he molecule is only the third example of a branched molecule. Interestingly, in the two previous examples iso-propyl cyanideA. Belloche et al., Science 345 (2014) 1584.nd iso-propanol,A. Belloche et al., Astron. Astrophys. 662 (2022) A110.he straight chain isomers where more abundant by factors of 2.5 and 1.8, respectively. Hence, we embarked on a study of the rotational spectrum of 1-butene,The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via the collaborative research center SFB 1601, project areas A4 and Inf, and through the Gerätezentrum "Cologne Center for Terahertz Spectroscopy".hose microwave spectrum was studied only to some extent for the syn and the slightly higher gauche conformers before.S. Kondo et al., J. Mol. Spectrosc. 28 (1968) 471.e will present the results of our ongoing laboratory study and of a search for the molecule in G+0.693-0.027.

---

Footnotes:

M. Fatima et al., Astron. Astrophys. 680 (2023) A25.T A. Belloche et al., Science 345 (2014) 1584.a A. Belloche et al., Astron. Astrophys. 662 (2022) A110.t The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via the collaborative research center SFB 1601, project areas A4 and Inf, and through the Gerätezentrum "Cologne Center for Terahertz Spectroscopy".w S. Kondo et al., J. Mol. Spectrosc. 28 (1968) 471.W

Methanol is not only the most abundant saturated organic molecule in interstellar space, but also a parent species of more complex organic molecules. It is often observed as a benchmark species to evaluate the abundance of larger organic molecules in Hot Core and Hot Corinos around protostars. However, this molecule exhibits internal rotation of a methyl group, which causes complex line patterns in a wide frequency range, and thus it makes difficult to calculate transition probabilities as well as frequencies for some spectral lines without using an appropriate Hamiltonian and code. In the case of major transitions, precise evaluation of the abundance is more intricated due to the effect of optical thickness and other factors. Therefore, it is useful to observe rare isotopologues such as CH₃¹⁸OH and CH₃¹⁷OH based on precise spectroscopic studies. Investigation of ¹⁸O and ¹⁷O abundance relative to ¹⁶O also provides a clue to understand a phase of nucleosynthesis. The synthesis of ¹⁷O is considered to be a consequence of hydrogen burning in stars via both cold and hot CNO cycles, and ¹⁶O and ¹⁸O have their origin in helium-burning. In other words, ¹⁷O is predominantly ejected by intermediate-mass stars through a longer production timescale while ¹⁸O is primarily synthesized in massive stars. Investigation of ¹⁸O/¹⁷O is so far conducted by observing CO isotopologues. However, CH₃OH isotopologues could be an alternative tool to study the ratio. Based on the spectroscopic data obtained from our group, we here report the first detection of CH₃¹⁷OH in hot region around a protostar together with the abundance of CH₃¹⁷OH relative to other methanol isotopologues.

Over 300 molecules have now been detected in the interstellar medium, but the carriers for many detected spectral features remain unidentified. We have a database of spectral line surveys from the Caltech Submillimeter Observatory (CSO) that provides information for 30 molecule-rich sources in the frequency range of  220 – 260 GHz. While initial assignments to these spectra are complete, many molecules that have been studied in the laboratory have not yet been compared to these observations. Our research group has a catalog of molecular information that can be compared to this rich set of astronomical data. The initial target molecules for this work include but are not limited to glycolic acid, dihydroxyacetone, glycolaldehyde, hydroxymethyl radical, glycolamine, and propylene oxide. The comparison of these spectra will be performed using the Global Optimization and Broadband Analysis Software for Interstellar Chemistry (GOBASIC). This talk will give the details of these searches and discuss the implications of the findings.

Heterocycles play a crucial role in the formation of life, as is exemplified by the nucleotide bases in our genetic material. Despite their significance, the detection of these compounds in the interstellar medium (ISM) remains limited. Previous observations identified gas-phase heterocyclic compounds primarily in warm, active star-forming regions, raising questions about their formation and distribution. The recent discovery of oxirane in the cold prestellar core L1689B demands for further investigation of heterocycle distribution in the ISM, and studying rotational spectra of heterocyclic molecules in the laboratory is crucial for successful radio astronomical detection. Here, we present the extended rotational spectrum of the heterocyclic molecule 3,4-dihydro-2H-pyran (34DHP, C₅H₈O). A combination of chirped-pulse Fourier transform microwave (CP-FTMW) and cavity-enhanced FTMW spectroscopy experiments were carried out to collect a total number of 319 transitions. The selected frequency bands extend ranges from 7 to 40 GHz using the cavity-enhanced FTMW spectrometer, while the CP-FTMW spectroscopy covers both the millimeter-wave range (E-band) from 68 to 90 GHz and an additional room temperature spectrum in the 18 to 26 GHz region (K-band) that can directly be compared to previous work. Using the computed rotational spectrum resulting from the newly determined molecular constants for 34DHP, we perform an upper limit search of this heterocycle in the dark and cold Taurus Molecular Cloud (TMC-1). We discuss the current limitations in understanding heterocyclic chemistry in the ISM and how further observations might contribute to unraveling the mysteries of interstellar heterocycles and their potential role in prebiotic chemistry.

2,3-Butadienal can be considered as a serious candidate for the interstellar medium since several aldehydes have already been detected including α, β-unsaturated derivatives such as propenal (H₂C=CH-CHO)Hollis, J. M.; et al., 2004, ApJ 610, L21, 10.1086/423200nd propynal (HCC-CHO).Irvine, W. M.; et al., 1998, ApJ 335, L89, 10.1086/185346oreover, the recent detection of several allenic compounds such as allenylacetylene (H₂C=C=CH-CCH)Cernicharo, J.; et al., 2021, A&A 647, L3, 10.1051/0004-6361/202140482nd allenylbutadiyne (H₂C=C=CH-CC-CC-H)Cernicharo, J.; et al., 2022, A&A 663, L3, 10.1051/0004-6361/202243857ead us to associate allenic and aldehydic functions.
2,3-butadienal has been synthesized by a new approach, the oxidation of the 2,3-butadienol by the Dess-Martin reagent. It must be stored at low temperature under liquide nitrogen. The spectra of trans conformer, which is then most stableBadawi, H. M.; et al., 1998, J. Mol. Struct. 428, 247, 10.1016/S0166-1280(97)00288-1 were recorded in Lille from 150 to 500 GHz using FLASH (Fast Lille Absorption emiSsion High resolution) spectrometer. The spectroscopic results 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.

---

Footnotes:

Hollis, J. M.; et al., 2004, ApJ 610, L21, 10.1086/423200a Irvine, W. M.; et al., 1998, ApJ 335, L89, 10.1086/185346M Cernicharo, J.; et al., 2021, A&A 647, L3, 10.1051/0004-6361/202140482a Cernicharo, J.; et al., 2022, A&A 663, L3, 10.1051/0004-6361/202243857l Badawi, H. M.; et al., 1998, J. Mol. Struct. 428, 247, 10.1016/S0166-1280(97)00288-1,

Phosphorus is an important element to life as a building block of DNA. Organophosphines are a class of molecules that have still not been detected in the interstellar medium, despite their similar structure to several nitrogen containing molecules. Phosphinoacetonitrile (PH₂CH₂CN) has potential interest for searches in space, as it is structurally similar to the glycine precursor aminoacetonitrile which has already been found in space, except that the nitrogen has been replaced with a phophorus atom. To enable a future astronomical search, Phosphinoacetonitrile has been synthesized and its millimeter wave rotational spectrum taken between 150-500 GHz using the FLASH (Fast Lille Absorption emiSsion High-resolution) spectrometer. The details of assignment will be discussed.

Following recent discoveries in the interstellar medium of the first cyclic and polycyclic aromatic hydrocarbons using rotational spectroscopy, namely benzonitrile (c-C₆H₅-CN) and cyanonaphthalene (c-C₁₂H₇-CN) McGuire, Burkhardt et al., Science 359.6372, 202-205 (2018); McGuire, Loomis et al., Science 371.6535, 1265-1269 (2021) renewed attention is given to derivatives of aromatic molecules and large carbonaceous species. The presence of a -CN group, for instance, significantly increases the permanent dipole moment value of a carrier compared to the parent species, enhancing carrier detectability in the interstellar medium. For species whose parent molecule possesses a permanent dipole moment, it is possible to study the column density ratios between substituted and unsubstituted species; some examples include indene (c-C₉H₈ v.s. c-C₉H₇-CN)Burkhardt, Lee et al., ApJL 913.2, L18 (2021); Cernicharo, Agúndez et al., A&A 649, L15 (2021); Sita, Changala et al., ApJL 938.2, L12 (2022)nd cyclopentadiene (c-C₅H₆ v.s. c-C₅H₅-CN)McCarthy, Lee et al., Nat. Astron. 5.2, 176-180 (2021) Other polar groups may render certain molecules detectable but laboratory data on these species is often lacking. In this context, we have undertaken laboratory spectroscopic investigations of the pure rotational spectrum of several polar naphthalene derivatives (containing a -CN, -CH₃, -SH, -NH₂, C₂H, or -C₂H₃ group) at millimeter and submillimeter wavelengths. We employed both a chirped-pulse millimeter-wave and frequency-modulation (sub)millimeter-wave spectrometers to record room-temperature spectra from 75 to 220 GHz. Some species have already been investigated at microwave wavelengths in the literatureSchnitzler, Zenchyzen, and Jäger, ApJ 805, 141 (2015); McNaughton, Jahn et al., MNRAS 476, 5258 (2018); Cabezas, Peña, and Cernicharo, MNRAS 519, 2590 (2022); Saragi, Calabrese et al., JPCL 14, 207 (2023) for others we report the first laboratory observation by means of pure rotational spectroscopy. For the latter, spectroscopic assignments were guided by quantum-chemical calculations. In this talk, we report on the measurement and assignment of the different spectra.

---

Footnotes:

McGuire, Burkhardt et al., Science 359.6372, 202-205 (2018); McGuire, Loomis et al., Science 371.6535, 1265-1269 (2021), Burkhardt, Lee et al., ApJL 913.2, L18 (2021); Cernicharo, Agúndez et al., A&A 649, L15 (2021); Sita, Changala et al., ApJL 938.2, L12 (2022)a McCarthy, Lee et al., Nat. Astron. 5.2, 176-180 (2021). Schnitzler, Zenchyzen, and Jäger, ApJ 805, 141 (2015); McNaughton, Jahn et al., MNRAS 476, 5258 (2018); Cabezas, Peña, and Cernicharo, MNRAS 519, 2590 (2022); Saragi, Calabrese et al., JPCL 14, 207 (2023);

Acylium ions, R−CO⁺, form an interesting family of astronomical molecules that has attracted recent interest through detections of the HC₃O⁺ and CH₃CO⁺ species towards the prototypical dark cloud TMC-1.J. Cernicharo, N. Marcelino, M. Agúndez et al. 2020, Astron. Astrophys. 642, L17^,J. Cernicharo, C. Cabezas, S. Bailleux et al. 2021, Astron. Astrophys. 646, L7he closely related linear acylium ion cyanooxomethylium, NCCO⁺, has been detected spectroscopically only very recently by its low−resolution vibrational spectrumO. Asvany, M. Bast, S. Schlemmer, and S. Thorwirth, 75th International Symposium on Molecular Spectroscopy 2022, WG03ollowed by a high−resolution study of its _2 fundamental mode at 2150 cm⁻¹ using leak−out spectroscopy.M. Bast, J. Böing, T. Salomon et al., 76th International Symposium on Molecular Spectroscopy 2023, RG07ere, we present the detection of the pure rotational spectrum of NCCO⁺ accomplished using the recently built 10K 22−pole ion trap apparatus COLtrap IIM. Bast, J. Böing, T. Salomon et al. 2023, J. Mol. Spectrosc. 398, 111840nd a novel infrared−millimeter−wave double−resonance scheme.O. Asvany, S. Thorwirth, P. C. Schmid et al.. 2023, Phys. Chem. Chem. Phys. 25, 19740verall, sixteen pure rotational transitions have been measured between 82−127 GHz and 164−246 GHz allowing for an accurate determination of the ground state rotational constants B and D J. Cernicharo, C. Cabezas, S. Bailleux et al. 2021, Astron. Astrophys. 646, L7TO. Asvany, M. Bast, S. Schlemmer, and S. Thorwirth, 75th International Symposium on Molecular Spectroscopy 2022, WG03fM. Bast, J. Bing, T. Salomon et al., 76th International Symposium on Molecular Spectroscopy 2023, RG07HM. Bast, J. Böing, T. Salomon et al. 2023, J. Mol. Spectrosc. 398, 111840aO. Asvany, S. Thorwirth, P. C. Schmid et al.. 2023, Phys. Chem. Chem. Phys. 25, 19740O

Methyl formate, acetic acid, and glycolaldehyde compose an isomeric family that is abundant in the interstellar medium, and whose astronomical observed relative abundances are commonly used to gain insights into the potential formation pathways of these complex organic molecules (iCOMs). Several of the proposed synthesis routes involve their protonated analogues. However, to date only limited spectroscopic data is available on any of the protonated isomers, hampering their astronomical detection that might shed light on specific formation pathways. Here, we present the first broadband vibrational study of protonated methyl formate, acetic acid, and glycolaldehyde (m/z 61, [C₂H₅O₂]⁺). The protonated species were formed in a storage ion source by electron impact ionization of the respective vapors (the dimer in the case of glycolaldehyde) and subsequent (self-)protonation reactions. The vibrational spectra of the mass-selected ions were recorded in the range 650 − 1800 cm⁻¹ using Ne-tagging infrared predissociation spectroscopy in the cryogenic 22-pole ion trap instrument FELion coupled to the infrared free-electron lasers at the FELIX LaboratoryJusko, P. et al., Faraday Discuss. 245 (2019) 221-244. The experimental spectra were compared to calculated vibrational frequencies obtained at the B2PLYPD3/aug-cc-pVTZ level of theory. Protonated forms of both structural conformers of methyl formate (syn and anti) were observed and assigned, with protonation on the carbonyl oxygen in the trans (lowest energy conformer) and cis orientation, respectively. Dominantly the lowest energy conformer (E,Z) of carbonyl-protonated acetic acid was observed when using acetic acid as precursor, and some potential isomerization to protonated glycolaldehyde will be discussed. When using the glycolaldehyde dimer as precursor, the lowest energy isomers of both protonated glycolaldehyde and acetic acid were observed.

---

Footnotes:

Jusko, P. et al., Faraday Discuss. 245 (2019) 221-244..

The rotational spectrum of the carbon chain cation C₅H⁺ has been measured at high resolution by Fourier transform microwave spectroscopy of a supersonic molecular beam. Six transitions between 9 and 39 GHz measured to better than 0.2 ppm allow the rotational and centrifugal distortion constants to be determined to high precision. The derived spectroscopic constants agree precisely with ones derived from four sharp rotational emission lines detected recently toward the cold dark cloud TMC-1,Cernicharo, J., Agúndez, M., Cabezas, C. et al., 2022 A&A 657, L16hus confirming the astronomical identification of C₅H⁺. The production of C₅H⁺ in dc discharges of dilute hydrocarbon gases prior to the supersonic expansion, its abundance relative to the smaller carbon chain cation C₃H⁺, and the prospects for the detection of larger carbon chain cations in the laboratory are also discussed.

---

Footnotes:

Cernicharo, J., Agúndez, M., Cabezas, C. et al., 2022 A&A 657, L16t

The conformer-specific temperature programmed desorption (TPD) of binary ice mixtures of n-propanol (n-PrOH) and water is interrogated via broadband rotational spectroscopy in the mm-wave regime. This method provides a quantitative, structure-specific probe into the 5 symmetry-unique conformers of n-PrOH, all of which are close in energy with low barriers to interconversion. Alcohols, including n-PrOH, have been observed in astrochemical environments where accretion onto water-containing ice grains occurs and is essential to the chemistry responsible for the synthesis of complex organic molecules. The slow process of TPD provides an experimental analogue to that which occurs in the interstellar medium as icy grains approach warmer regions of space and undergo sublimation. In this work, we apply Chirped-Pulse mm-wave spectroscopy of buffer gas cooled molecules desorbed from an Ice surface (CPICE) and track the evolution of the conformer desorption profiles over varying mixing ratios of n-PrOH and water. In comparison with neat n-PrOH ices, the addition of water results in significant changes both in terms of the conformers present in the ice and their respective abundances within. Each binary water and n-PrOH ice mixture exhibits distinct TPD profiles with reduced binding energies, highlighting the importance of water interactions in ice grain chemistry and desorption.