During the process of star formation, radiative and thermal processing of icy grain mantles leads to the formation of complex organic molecules (COMs). This protostellar processing produces the bulk chemical inventory which is subsequently delivered to forming planetary systems. To investigate this process, we have used the Sublimation Laboratory Ice Millimeter/submillimeter Experiment (SubLIME) on water:methanol interstellar ice analogs at a variety of ratios to study the dependence of organic molecule formation on the concentration of methanol to water. The results of these experiments will be compared to the λ = 2 mm astronomical observations of the W3 star-forming region using the NOrthern Extended Millimeter Array (NOEMA). From these observations, we have imaged and analyzed molecular distributions in the neighboring star-forming cores W3(H₂O) and W3(OH). By comparing the ratios of COMs produced in the laboratory ice experiments to those observed in W3, we will discuss astrochemical implications for the ice and gas composition in these active star-forming regions.

Accurate models of interstellar chemistry enable predictions of the chemical inventory of molecular clouds. Observations probing the effects of physical conditions of interstellar clouds on their chemical complexity allow the refinement of astrochemical models. To this end, we observed ten sources including hot cores, hot corinos, Class 0 protostars, HII regions, and shocked regions using Herschel HIFI Bands 2 and 5 in 12 GHz windows centered at 670 GHz and 1.16 THz. We constrained the temperatures and column densities of detected complex organic molecules using GOBASIC, a global fitting algorithm which performs Boltzmann analyses under the assumption of local thermodynamic equilibrium. Here we present the observations and comparisons of the molecular abundances to the physical properties of their environments for benchmarking of astrochemical models.

We present a joint laboratory, theoretical, and astronomical study of several new metal-carbon clusters including the alkaline earth metal-bearing molecules MgC₂, CaC₂, and SrC₂, as well as the closely related rare earth molecule YbC₂. We have synthesized these species in the laboratory with a laser-ablation supersonic expansion source and detected their rotational spectra at high resolution with cavity Fourier transform microwave spectroscopy. Combining extensive isotopic measurements with highly accurate ab initio rovibrational calculations, we have derived their precise semi-experimental equilibrium geometries, which are all T-shaped with highly ionic metal-carbon bonds. Our measured laboratory rest frequencies have enabled the identification of MgC₂ and CaC₂ as the carriers of several strong, previously unassigned radio emission lines in the circumstellar envelope of the well known evolved carbon-rich star IRC+10216. These laboratory and astronomical discoveries yield fundamental insights into the chemical structure and bonding of s- and f-block metal compounds, and place critical new constraints on the postulated astrochemical pathways that incorporate metal atoms into complex polyatomic molecules. Our work suggests that larger metal-carbon clusters may now be detectable in the laboratory and in circumstellar environments, providing a new probe of the formation of refractory metal-carbon particles.

The laboratory and astronomical discovery of the metal dicarbides, MgC₂ and CaC₂, discussed in the preceding talk represents a key advance in the study of metal carbides and fills a longstanding gap in the molecular inventory of evolved carbon stars. In this talk we will discuss how characterizing the distribution of the two species in IRC+10216, together with a careful analysis of their excitation and abundance might help elucidate the role of metals in the chemistry of IRC+10216, and the state of refractory elements in carbon-rich circumstellar environments more generally. We will also discuss the utility of dicarbides as physico-chemical probesPossessing dipole moments of nearly 8 D and 11 D, MgC₂ and CaC₂ are among the most polar molecules detected in IRC+10216, and consequently strong discriminators between radiative and collisional excitation processes.f circumstellar regions, as well as the prospects of detecting larger metal-carbon compounds there.

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Footnotes:

Possessing dipole moments of nearly 8 D and 11 D, MgC₂ and CaC₂ are among the most polar molecules detected in IRC+10216, and consequently strong discriminators between radiative and collisional excitation processes.o

In recent years, astrochemistry has shown that interstellar chemistry is able to generate several building blocks of key biomolecules. These investigations aim the detection of new interstellar systems, especially those that have a relevant prebiotic role, such as peptide-like molecules. Herein, we present the laboratory detection and astronomical search for acetohydroxamic acid (CH₃CONHOH), an uncharted glycine isomer. We provide frequencies of its ground state (up to 40 GHz), measured by broadband and narrowband rotational spectroscopies combined with a laser ablation device. The ¹⁴N nuclear quadrupole hyperfine structure and the A-E splittings due to the internal rotation were resolved and interpreted. Hence, we determined a precise set of the rotational spectroscopic parameters for the two distinct Z- and E-conformers. M. Sanz-Novo, J. L. Alonso, V. M. Rivilla, B. A. McGuire et al. 2022, A&A, 666, A134.ur laboratory data were subsequently employed to search for the lowest-energy Z-conformer toward two prominent astronomical sources. Firstly, we used the spectral GOTHAM survey performed with the Green Bank Telescope to search for the molecule toward the cold molecular cloud TMC-1. We also employed a sensitive spectral survey of the Galactic Center molecular cloud G+0.693-0.027, based on IRAM 30 m and Yebes 40 m observations. We report the nondetection of acetohydroxamic acid toward both astronomical sources but, interestingly, the derived upper limit to its column density lies close to that obtained glycine. Its corresponding molecular abundance with respect to molecular hydrogen is found to be ≤ 1 × 10⁻⁹ and 2 × 10⁻¹⁰ in TMC-1 and G+0.693-0.027, respectively, which further constrain the abundance of this glycine isomer in the ISM and provide additional insights into the chemistry of amino acid-related species in space.

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Footnotes:

M. Sanz-Novo, J. L. Alonso, V. M. Rivilla, B. A. McGuire et al. 2022, A&A, 666, A134.O

Ethanolamine (NH₂CH₂CH₂OH, EtA), a key molecular component of phospholipids in cell membranes, has been recently detected in the G+0.693 molecular cloud¹. This same molecule was detected in the Almahata Sitta meteorite as well. In this case, its formation has been suggested to be due to the unusual thermal conditions that might have caused the decomposition of amino acids². On the other hand, its formation route in the interstellar medium (ISM) is suggested in a work led by Charnley et al. 2002³. Due to the addition of a carbon atom to CO, through subsequent hydrogenation and nitrogenation steps of the already detected HCCO radical intermediate, it might be possible to produce EtA. Additionally, a recent study showed the NH₃+CO+C reaction to be a barrier-less process, paving the way to an alternative route to the formation of EtA precursors in the ISM⁴. We herein perform a comprehensive quantum chemical analysis of the isomers involved in the EtA formation pathway. We extend the ensemble of isomers that can take part in this route, and we compute the energy of those that might be acting as crucial actors in the chemical steps. We optimise their molecular geometry and obtained a set of rotational and distortion constants at a high level of theory to assist their spectroscopic characterization for their future interstellar search.

¹Rivilla, V. M. et al. PNAS, 118, 22 (2021)
²Glavin, D.P. et al. 45, 10-11 (2010)
³Charnley, S.B., et al. Earth, Moon, and Planets, v. 90, Issue 1, p. 349-360 (2002)
⁴Krasnokutski, S.A. et al. Nat Astron 6, 381–386 (2022)

The interstellar molecule l-C₃H⁺ appears to be the most sensitive and definitive molecular tracer of enhanced UV-flux ever observed in the ISM. Extensive, deep searches for this species in dozens of sources show its presence nearly exclusively in UV-enhanced regions. Yet, our understanding of the spatial distribution of the molecule within these sources, and the excitation conditions (and abundances) in previously-observed regions, is sorely lacking. I will discuss recent ALMA observations of l-C₃H⁺ in the Horsehead PDR region that have revealed an unexpected large-scale distribution of l-C₃H⁺. With these data we wish to better understand the spatial distribution, abundance, and excitation of this potentially transformational molecule in our ability to probe the extent of UV-enhanced flux in these and other key regions. The results will be used to refine state-of-the-art PDR chemical modeling codes.

Light travelling from far-off stars interacts with interstellar molecules, ice grains, and dust particles, which can show up in astronomical observations. These observations reveal the results of scattering, absorption, and emission across the spectrum. In the ultraviolet region, the wavelength of light is of comparable size to the dimensions of dust particles. This enhances scattering, giving rise to the ultraviolet extinction curve. In photoionizing regions of space, there exists an additional feature of an intense absorption “bump” on this curve at 217.5 nm. The massive intensity of this feature requires that the carrier be made from very abundant interstellar element(s), so many studies have focused on the spectra of polyaromatic hydrocarbons or graphite-containing particles to identify the carrier, but no match has been found. Here, we measure the ultraviolet spectra of ionized carbon monocyclic rings (C_n⁺, n = 13 – 19) which are produced by laser vaporization using mass selection and tunable laser photodissociation spectroscopy. The resulting spectra show that ionized carbon rings have the ultraviolet spectra and relevant astrochemistry to explain the bump.

Using data from the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) survey, we report the first astronomical detection of the C₁₀H⁻ anion. The astronomical observations also provided the necessary data to refine the spectroscopic parameters of C₁₀H⁻. From the velocity stacked data and the matched filter response, C₁₀H⁻ is detected at > 9σ confidence level at a column density of 4.04^+10.67_−2.23×10¹¹ cm⁻². A dedicated search for the C₁₀H radical was also conducted towards TMC-1. In this case, the stacked molecular emission of C₁₀H was detected at a  ∼ 3.2σ confidence interval at a column density of 2.02^+2.68_−0.82×10¹¹ cm⁻². However, since the determined confidence level is currently < 5σ, we consider the identification of C₁₀H as tentative. The full GOTHAM dataset was also used to better characterize the physical parameters including column density, excitation temperature, linewidth, and source size for the C₄H, C₆H and C₈H radicals and their respective anions, and the measured column densities were compared to the predictions from a gas/grain chemical formation model and from a machine learning analysis. Given the measured values, the C₁₀H⁻/C₁₀H column density ratio is  ∼ 2.0^+5.9_−1.6 - the highest value measured between an anion and neutral species to date. Such a high ratio is at odds with current theories for interstellar anion chemistry. For the radical species, both models can reproduce the measured abundances found from the survey; however, the machine learning analysis matches the detected anion abundances much better than the gas/grain chemical model, suggesting that the current understanding of the formation chemistry of molecular anions is still highly uncertain.

A new receiver has been constructed for the 12 m telescope of the Arizona Radio Observatory (ARO). The receiver package consists of four separate, dual polarization, frequency bands in a modular cryostat. The four bands cover the astronomically important atmospheric windows at 1.2, 2, 3, and 4 mm wavelengths. In the 3 mm and 1.2 mm wavelength regions, the receiver employs ALMA Band 3 (84 - 116 GHz) and ALMA Band 6 (211 - 275 GHz) sideband-separating (SBS) SIS mixers, while at 4 mm (67 - 90 GHz), cryogenic HFET amplifiers are used. Sideband separation for the 4 mm band is achieved through a room temperature E band downconverter developed at ARO. The 2 mm band (125 - 180 GHz) consists of SBS mixers developed from the device level by ARO in collaboration with the Central Development Laboratory (CDL) at the National Radio Astronomy Observatory (NRAO) and the University of Virginia Innovations in Fabrication Laboratory. The 2 mm window is accessible by a single broadband mixer, which covers all of ALMA Band 4 and 40% of ALMA Band 5. The mixer chip has a series array of four SIS junctions, similar to ALMA Bands 3 and 6. The new 2 mm mixers have typical noise temperatures less than 45 K with image rejection greater than 15 dB at most frequencies. The 2 mm mixers have proven to be exceptionally robust, with system temperatures around 100 K on the sky and with excellent baseline stability. The backend used for the receiver is the ARO Wideband Spectrometer (AROWS). AROWS is a digital Fourier transform spectrometer with a sampling rate of 10 Gs per sec, and can be configured to produce 2 x 4 GHz of continuous and usable instantaneous bandwidth. The digitizer card was developed by Curtiss-Wright. Two such cards can be used to generate 16 GHz of instantaneous bandwidth (4 x 4 GHz), allowing all four IF channels of any receiver band to be processed simultaneously for observations.