Iron, one of the most prevalent and abundant elements in the universe, is important both astrophysically and astrobiologically. Although gaseous atomic iron has been identified in stellar photospheres, H II regions, and planetary nebulae, it remains elusive in molecular form. Based on previous laboratory work in the Ziurys group, a new iron-bearing molecule, FeC (X ³∆_i), has been identified in interstellar gas. The radical was discovered towards the carbon-rich asymptotic giant branch (AGB) star IRC+10216, using the Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) at 1.3 mm and the ARO 12-m telescope at 2 mm. The J = 4→3, J = 5→4, and J = 6→5 rotational transitions of FeC in the lowest spin-orbit ladder, Ω = 3, were measured in this source. FeC is the second iron-bearing molecule conclusively detected in the interstellar medium and is the first identification of a metal carbide. The fractional abundance of FeC, relative to H₂, was determined to be f  ∼  6 × 10⁻¹¹, with a shell distribution peaking at a radius of 300 R_* and extending out to 500 R_*. A new analysis of FeCN, the only other known iron-containing species, also observed in IRC+10216, indicates that this radical extends out to 800 R_* with f  ∼  8 × 10⁻¹¹. The formation of FeCN may therefore be linked to the destruction of FeC.

VY Canis Majoris (VY CMa), a hypergiant star, offers an intriguing platform for studying the chemistry in the ejecta of massive stars. VY CMa experiences intense, non-spherical mass loss, generating asymmetric outflows that create intricate structures comprised of dust and gas in the circumstellar envelope. Employing ALMA at Band 6, the refractory molecules NaCl, Na³⁷Cl, KCl, and K³⁷Cl were imaged with 0.25" and 1" resolutions. The ALMA data were combined with single-dish observations from the Arizona Radio Astronomy Observatory Submillimeter Telescope (ARO SMT) to recover all flux. The sensitivity is significantly improved from previous NaCl ALMA images. This work is also the first identification of KCl in the envelope of VY CMa. NaCl displays emission centered on the central star extending out to  ∼  50 R_*. It also distinctly traces an ejected cluster of knots called the “SW Clump,” located at a distance of about 180 R_*. KCl exhibits a similar, two-source distribution. The SW Clump may represent material directly expelled from the stellar photosphere, suggesting that NaCl and KCl form very quickly in energetic ejecta.

The envelope of the oxygen-rich, hypergiant star VY CMa has been found to be far more chemically rich in molecules than previously thought, with the presence of metal oxides and hydroxides. To explore the spatial relationship between the metal-bearing species, observations with ALMA at Band 6 with resolutions of 0.25 and 1 arcseconds have been conducted of AlO, AlOH, and TiO₂. Combining these data with single-dish spectra from the Arizona Radio Astronomy Observatory (ARO) Submillimeter Telescope (SMT), complete images of these three molecules have been created. The images show that AlO emission extends about 60 R_*, centered on the star, with TiO₂ having a very similar distribution. In contrast, the emission from AlOH is more confined, with a source radius of 40 R_*. All three molecules appear to display non-spherical distributions about the star, indicating that the inner envelope may also be experiencing asymmetric mass loss. These images also suggest rapid condensation of AlO and TiO₂ onto dust grains, while AlOH may be converted to AlO in gas-phase reactions.

r0pt Figure The diffuse interstellar bands (DIBs) are the longest unsolved mystery in molecular spectroscopy. They are a series of over 500 absorption features in near-IR and visible, observed through all sightlines within the interstellar medium (ISM). Despite over a century of research, only one molecule has been identified as a DIB carrier (C₆₀⁺)E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature 523, 322–323 (2015). One hypothesis attributes these features to carbonaceous radicals and cations present in molecular clouds, where they account for a large percentage of the cosmic carbon budget, and their identification will provide insight into the cosmic lifecycle of carbon. Small polycyclic aromatic hydrocarbons (PAHs), and the molecules they grow into, are of interest in these experiments, as their discovery in the ISM may reveal information on the chemical pathways which form these, and eventually larger, molecules. Radical targets were prepared using a pulsed high-voltage discharge and supersonic expansion, with these molecules then analyzed using laser induced fluorescence (LIF), dispersed fluorescence (DF), and resonance-enhanced multiphoton ionization (REMPI) spectroscopy. This research reveals that the electronic transition of a PAH growth product, a neutral radical of a substituted bicyclic hydrocarbon, is coincident with a weak DIB, λ4689 (see figure), thus making it a plausible candidate DIB carrier. This presentation will include a detailed methodology of this experiment, the experimental data used for structure determination, comparisons to interstellar data, and astrochemical implications.

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Footnotes:

E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature 523, 322–323 (2015)..

Cool red giant stars exhibit absorption bands of calcium monochloride (CaCl) in the optical part of their spectra. In this work, the bands of CaCl corresponding to the A²Π−X²Σ⁺ transition with v′ ≤ 4 and v^′′ ≤ 4 and B²Σ⁺−X²Σ⁺ transition with v′ ≤ 2 and v^′′ ≤ 2 are rotationnally analyzed with PGOPHER. All bands were analyzed using high resolution absorption spectra collected at the National Solar Observatory in 1985 (Kitt Peak, Arizona), calibrated with atomic lines from a high resolution emission spectrum obtained in a separate hollow cathode experiment. The results are compared with previous laser-induced fluorescence measurements. Overall, the accuracy of spectroscopic constants for the A²Π and B²Σ⁺ states is improved. Scaled transition dipole moment calculations were used to calculate line lists, which can be used to determine CaCl stellar abundances. Additionally, isotope splittings allowed us to estimate band origins for the ⁴⁰Ca³⁷Cl isotopologue based on bandhead positions.

ZrO is a well-studied transition metal monoxide because of its astrophysical importance. The bands of d³ Φ - a³ ∆ system with v^′ ≤ 4 and v^′′ ≤ 5 are rotationally analyzed using the PGOPHER program to provide updated spectroscopic constants. In addition, we have preliminary analyses for the f³ ∆ - a³ ∆, e³ Π - a³ ∆, and b³ Π - a³ ∆ band systems based on emission spectra from a high-temperature carbon furnace. New ab initio calculations of transition dipole moments were performed using the MOLPRO quantum chemistry package. The calculated transition dipole moments and spectroscopic constants are employed to determine band strengths. The spectroscopic constants along with the band strengths are used to calculate line lists that can be used to determine Zr abundances in S-type stars.

Comets are small icy bodies that are leftovers of the formation of the Solar system. As they are now located very far from the Sun, their composition have remained pristine, and they are considered fossils of our Solar system, containing crucial information about the conditions that prevailed nearly five billion years ago. The majority of comets observations are made from the ground when comets come closer to the Sun and start sublimating, revealing their inner composition through the formation of a coma. Among the limited number of space missions dedicated to cometary science, the spacecraft Rosetta launched in 2004 significantly enhanced our understanding of those small bodies, by conducting a two-year study of the comet 67P/Churyumov-Gerasimenko. One of Rosetta's instrument, the mass spectrometer ROSINA, discovered numerous chemical species in the coma that had never before been observed in cometsAltwegg, K. (2017). Chemical highlights from the Rosetta mission. Proceedings of the International Astronomical Union, 13(S332), 153-162. Given the rarity of space missions, these findings must be generalized to ground-based cometary observations to improve our overall understanding of comets. From high-resolution spectra obtained at the AILES beamline of the SOLEIL synchrotron facility and at the LISA facility in Créteil, positions and intensities of emission lines of three vibrational bands of chloromethane (CH₃Cl) and one vibrational band of cyanogen (C₂N₂) were obtained. Those two cometary molecules detected by ROSINA are yet to be detected from ground-based observations. A cometary fluorescence model for one of the band of chloromethane is currently being developed from our derived parameters. This model will allow us to investigate the presence of this molecule in cometary spectra.

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Footnotes:

Altwegg, K. (2017). Chemical highlights from the Rosetta mission. Proceedings of the International Astronomical Union, 13(S332), 153-162..

We discuss observations of the A−X (0−0) and (1−0) bands of the CN red system in absorption along heavily-reddened sight lines through diffuse molecular clouds. Our observations were obtained with the Habitable-zone Planet Finder on the Hobby-Eberly Telescope at McDonald Observatory. High-resolution, high signal-to-noise ratio near infrared spectra were obtained for the lines of sight to HD 28975, HD 29647, HD 169754, Cyg OB2 12, and HD 204827. These data represent the first extensive set of observations of the CN A−X (0−0) and (1−0) bands in interstellar clouds. The red system bands allow us to obtain accurate CN column densities and rotational excitation temperatures for molecule-rich sight lines where the B−X (0−0) band at 3874 Å is typically strongly saturated. Our results for heavily reddened sight lines are compared with similar results for more moderately reddened sight lines analyzed as part of an ongoing survey of CN rotational excitation based on observations of the B−X violet system using the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope and the Tull Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory. While most sight lines exhibit CN excitation temperatures that are consistent with the temperature of the cosmic microwave background, there is a systematic excess in T₀₁(CN) that may be due to local excitation by electron impact. We explore the dependence of these excess temperatures on various cloud properties.

The early history of our Solar System can be studied through observations of comets which characterize their coma chemistry, and by inference, the chemistry retained in their nuclei. Long-period comets, which can be thought of as pristine samples of our protoplanetary disk, afford an avenue to address the question of inheritance in astronomy—that is, does the chemistry from the earliest stages of star formation persist through the process of forming planets, moons, asteroids, and comets? As such, characterizing the chemistry of comets has become essential in testing the evolution of molecular material from the interstellar medium to the present day solar system. Near-simultaneous observations of long-period comet C/2022 E3 (ZTF) were obtained with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2023. The spatial distributions of water and methanol were simultaneously imaged with the JWST NIRSpec IFU through their ro-vibrational transitions, while ALMA obtained interferometric spatial-spectral maps of multiple methanol rotational transitions. Radiative transfer modeling was performed to test for spatial variations in the temperature and column density of both species throughout the coma. I will present our findings from this comparative study between ALMA and JWST, discuss the implications of our modeling results, and explore how future studies will help determine the chemical composition of cometary comae from the radio to the IR.

Radical species play a critical role in interstellar chemistry Herbst, International Reviews in Physical Chemistry, 36 287 (2017) as well as in atmospheric chemistry Rosado-Reyes, Francisco, Szente, Maricq, Frøsig Østergaard, The Journal of Physical Chemistry A, 109 10940 (2005) The methoxymethyl radical, CH₃OCH₂, produced from H-abstraction of dimethyl ether (DME) is an important intermediate in methyl formate (MF) formation Balucani, Ceccarelli, Taquet, International Reviews in Physical Chemistry, 449 L16 (2015) As both DME and MF are abundant in the interstellar medium (ISM), the radical CH₃OCH₂ is considered as a detectable species Gámez, Senent, The Astrophysical Journal, 913 21 (2021) However, experimental data on CH₃OCH₂ are scarce and no rotational data are available, as the laboratory characterization of large radicals remains tedious and requires specific experimental setups. Here, we present the study of the CH₃OCH₂ radical in the millimeter and sub-millimeter wave range. The radical was produced from CH₃OCH₃, similarly as in our recent studies of radicals Chahbazian, Martin-Drumel, Pirali, Journal of Physical Chemistry A, 128 370 (2024) and its spectrum was acquired using Faraday rotation spectroscopy Viciani, De Natale, Gianfrani, Inguscio, Optical Society of America, 16 301 (1999) Transitions with values of the rotational quantum numbers N" and K_a" up to 34 and 5 were measured and assigned. Because of the rotation of the methyl group, rotational levels are split into A and E rotation-torsion components, leading to the observation of doublets in our spectra Lin, Swalen, Reviews of Modern Physics, 31 841 (1959) I will briefly present the experimental details and focus on our preliminary analysis of the CH₃OCH₂ radical spectrum.

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Footnotes:

Herbst, International Reviews in Physical Chemistry, 36 287 (2017), Rosado-Reyes, Francisco, Szente, Maricq, Frøsig Østergaard, The Journal of Physical Chemistry A, 109 10940 (2005). Balucani, Ceccarelli, Taquet, International Reviews in Physical Chemistry, 449 L16 (2015). Gámez, Senent, The Astrophysical Journal, 913 21 (2021). Chahbazian, Martin-Drumel, Pirali, Journal of Physical Chemistry A, 128 370 (2024), Viciani, De Natale, Gianfrani, Inguscio, Optical Society of America, 16 301 (1999). Lin, Swalen, Reviews of Modern Physics, 31 841 (1959).

We describe a study providing measurements of the N(¹²C₂)/N(¹²C¹³C) ratio acquired with the Habitable-zone Planetary Finder (spectral resolution of 6 km s⁻¹ and signal-to-noise per resolution element from 1200 to 2000) on the Hobby-Eberly Telescope in West Texas. The focus is on absorption from the (1-0) band of the Phillips system (A¹Π_u−X¹Σ_g⁺) near 1 micron toward the stars HD 28975 and HD 29647, which respectively probe L1529 and Heiles Cloud-2. These data are supplemented by previously reported results on the N(¹²CO)/N(¹³CO) and N(¹²CN)/N(¹³CN) ratios from absorption at infrared and visible wavelengths and radio emission. Related results along the sight line toward HD 27778, which probes L1506, are incorporated into the analysis. Our findings to date reveal a N(¹²C₂)/N(¹²C¹³C) ratio of about 30, or an ambient ¹²C/¹³C ratio of about 60, toward HD 28975; such a value is consistent with expectations. However, toward HD 29647, only a lower limit for the N(¹²C₂)/N(¹²C¹³C) ratio of 100, or an ambient ¹²C/¹³C ratio greater than 200, is inferred. The results for this direction resemble those for C₂H at radio wavelengths in nearby portions of TMC-1. The chemical pathways in diffuse molecular gas for C₂ and C₂H are connected, and we are constructing models of chemical fractionation to examine the suite of measurements in depth. Comparisons between observational results and model predictions will also be presented.

Photodissociation regions, where intense ultraviolet radiation is impacting a molecular cloud, present some of the best laboratories for observing the effects of radiation on interstellar chemical evolution. Here, we present ALMA observations of the Horsehead Nebula PDR region. We use single-excitation temperature radiative transfer fits to obtain column density maps of 8 different species toward this region. These maps are, to our knowledge, the highest spatial resolution maps of chemical abundances toward this source so far and allow us to directly probe the abundance of these species as a function of depth into the PDR, which is directly proportional to the UV flux. Many routinely observed PDR-tracing molecules such as C¹⁷O, c-C₃H₂, and methanol are observed, but the primary target of our work was l-C₃H⁺. By comparison to these other species, we show that l-C₃H⁺ is the most sensitive tracer of the UV field. While the other species all display abundances ahead of or behind the PDR peak, l-C₃H⁺ uniquely traces the peak itself. We discuss the implications of this on the utility of these various species in tracing different physical conditions in UV-illuminated regions.