The T₂ time of HCN and HNC in He was measured at low temperatures using chirped pulse Fourier transform millimeter wave spectroscopy, to compare to scattering calculations and to investigate the difference of interaction between the two structural isomers. These molecules are commonly observed in the interstellar medium (ISM), where their abundance ratio can be used to elucidate conditions within an interstellar environment. Within these environments, they are expected to collide with He and H₂, which could lead to non-thermal excitation. Previous ab initio calculations of the collisions with He and H2 with HCN and HNC have shown that the rates for HNC with these colliders are much greater, despite their similarities in structure. We have performed CPUF (Chirped pulse in Uniform Flow) experiments to measure the difference in T₂ of HCN and HNC at cold temperatures in He. The J=1-0 transitions of HCN and HNC were observed in under CRESU (Reaction Kinetics in Uniform Supersonic Flow) conditions using cold flows of He. Pulsed laser photolysis of vinyl cyanide was used to produce HCN and HNC under comparable conditions. The T₂ time was fit directly from the free induction decays of these experiments at different temperatures, which is directly comparable to the linewidth in the frequency domain. This was then compared to pressure broadening cross sections produced from close coupling scattering calculations performed on ab initio potential energy surfaces. We find that there is a difference in interaction of HCN and HNC with He at low temperatures and will discuss the impacts this may have for observing these species in the ISM.

Heterocyclic organic compounds are assumed to play a pivotal role in Earth’s prebiotic chemistry. Imidazole is a five-membered aromatic ring containing two nitrogen nuclei. It is a vital part of various fundamental biological molecules, such as the amino acid histidine and purine nucleobases. While imidazole has been previously studied in the lower frequency regime ( < 40 GHz) [1], the study has been extended over a larger frequency range to improve centrifugal distortion constants for astronomical searches. Recently, we have extended the frequency range up to 295 GHz. The broadband rotational spectrum of imidazole was recorded in selected frequency regions (2-8, 13-15.5, 18-26, 75-110, and 260-295 GHz) and the rotational transitions for the parent molecule in the vibrationally ground state were assigned [2]. The present work focusses on the assignment of the rotational transitions for the singly substituted 13C - 15N isotopologues in their vibrationally ground states and the parent molecule in its vibrational excited states. The transitions for all of the species in the lower frequency region showed resolvable hyperfine splitting (HFS), because of the two 14N nuclei (I = 1). But in the higher frequency regime (75-295 GHz), the lines did not show detectable HFS and hence were assigned without taking HFS into account. This provided us with a new set of spectroscopic constants derived from the global fit, allowing for a more accurate determination of quartic and sextic centrifugal distortion constants. The isotopic data allowed for the deduction of the exact coordinates of the atoms and the precise structural determination of imidazole in the gas phase. The extended sets of rotational parameters obtained are essential for making accurate predictions for astronomers to use for observational searches in the interstellar medium in the millimeter-wave region.
References: [1] D. Christen et al. Z. Naturforsch., 37, 1378 (1982) [2] B. M. Giuliano et al. A&A 628, A53 (2019)

The circumstellar envelopes of asymptotic giant branch (AGB) and red supergiant (RSG) stars are known for their unique chemistry and efficient production of dust grains. Though dust grain composition and behavior at micron-size is well-studied in the ISM, the chemical processes leading to their formation are poorly understood from an observational lens. Thus, characterizing the reservoir of gas-phase molecules in the "Dust Production Zones" of evolved stellar envelopes (5-20 R*) is crucial to understanding the process of grain condensation. Thermochemical equilibrium models predict that a variety of light hydrides (XH) are abundant in these regions; however, only three such species have been observed in CSEs to-date (HCl, HF, and OH). Using SOFIA's GREAT receiver, we conducted a search for the diatomic hydrides SiH and PH toward two well-studied circumstellar envelopes: IRC+10216 and VY CMa. We present spectra for these objects ranging from 600 GHz to 1.5 THz, where most ro-vibrational emission comes from highly excited molecules near the stellar photosphere. Neither SiH nor PH were detected in these envelopes, likely owing to their weak dipole moments and severe beam dilution expected from molecules in the inner envelope. We calculated upper limit abundances for SiH and PH in IRC+10216 and VY CMa and discuss their implications for equilibrium chemistry and dust grain formation theories in these important astronomical laboratories.

Oxygen-rich supergiant stars undergo intense, sporadic mass loss often causing them to have highly directed, non-isotropic outflows. These outflows have been previously identified in the envelope of the supergiant VY CMa, both in the infrared and in molecular lines. In VY CMa, these flows are best traced by sulfur-bearing molecules SO₂ and SO. To further investigate the unusual properties of supergiant stars, we have conducted a 1 mm survey of another such object, NML Cyg. Two major asymmetric outflows have been identified in the envelope of NML Cyg in the spectra of SO and SO₂, one blue-shifted and the other red-shifted. Spectral line analysis with the radiative transport code ESCAPADE suggests that these two outflows are in random directions and are not bipolar in nature.

Sodium chloride, NaCl, is an essential molecule for life. Its presence in circumstellar envelopes of evolved stars, protoplanetary disks, and asteroids is highly surprising. Furthermore, it has two abundant isotopologues, Na³⁵Cl and Na³⁷Cl, and the chlorine isotopic ratio can be used to trace its chemical history. NaCl has been a known constituent of both the carbon star IRC+10216 and the oxygen-rich supergiant VY CMa, as was evident in a previous ARO 1 mm spectral survey of these objects. Recently, we have also detected this molecule in the supergiant NML Cygnus. Using the radiative transport code ESCAPADE, we have modeled multiple transitions of both Na³⁵Cl and Na³⁷Cl detected in the envelopes of IRC+10216, VY CMa, and NML Cyg. Surprisingly, the abundance of NaCl is similar in all three envelopes, with a fractional abundance of  10⁻⁹ relative to H₂, with a ³⁵Cl/³⁷Cl of approximately 3/1. The implications of these results will be discussed.

The PO molecule has been identified towards the Orion-KL region based on a 3mm survey carried out with the ARO 12m. Two transitions were observed, each consisting of lambda-doublets. The estimated abundance of this species in Orion is approximately 10⁻¹⁰, relative to molecular hydrogen. The PN molecule was also observed in the survey, suggesting PO/PN is approximately 1. Our results are consistent with the findings in other molecular clouds, and suggest that PO may be a relatively common molecule in star-forming regions.

The widespread presence of aromatic molecules in (pre-)planetary nebulae and evolved stars, as evidenced by the ubiquitous Unidentified Infrared Bands, suggests that a substantial portion of this material is formed in a `top-down' manner via the breakdown of carbon soot in circumstellar envelopes. The recent detection of benzonitrile (c-C<sub>6</sub>H<sub>5</sub>CN), a polar proxy for benzene (c-C<sub>6</sub>H<sub>6</sub>), in the prestellar molecular cloud TMC-1, however, suggests that `bottom-up' pathways to aromatic molecule formation may also be operative. We present new radio astronomical evidence of benzonitrile in four additional pre-stellar, and possibly protostellar, sources: Serpens 1A, Serpens 1B, Serpens 2, and MC27/L1521F. These detections establish that benzonitrile is not unique to TMC-1; rather aromatic chemistry appears more widespread throughout the earliest stages of star formation than previously thought. Initial analysis reveals the benzonitrile to cyanopolyyne ratio is consistent within a single parent cloud, indicating that the initial conditions and atomic/molecular reservoirs may be important to understanding the formation for simple aromatic molecules. We will also briefly discuss the expansion of this survey to an even wider range of sources.

Modern radio interferometers are changing, as expected, the way we look at the Universe. In particular, the unprecedented angular resolution and sensitivity are helping the observers to disentangle the complexity of the interstellar sources, spatially and chemically. Thanks also to the observable instantaneous bandwidth of modern receivers many molecular species can be observed at the same time. From these analyses several important information on the chemistry and kinematic of the observed regions can be derived, including chemical differentiation, isotopic fractionation, and inner physical composition of the cloud itself.
In this work, several maps of chemical compounds observed towards the protocluster OMC-2 FIR4, in the frame of SOLIS (Seeds Of Life In Space; Ceccarelli et al. 2017) large program at NOEMA, will be showed. In particular the observations presented will focus on the silicon and sulfur chemistry in this young protocluster in the Orion molecular cloud, which is one of the best and closest protocluster analog to the one in which the Solar System formed.

Recent observations of the evolved carbon star IRC+10216 with unprecedented high angular resolution have revealed a plethora of unassigned (U) rovibrational lines associated with the dust formation zone. Because SiC₂ is a known, abundant molecular constituent of this region, it is reasonable to posit that some fraction of the observed U lines arise from vibrationally excited levels of SiC₂ that are populated at elevated temperatures. At present, the radio band laboratory data that would permit testing of this hypothesis are largely absent: ab initio prediction of relevant spectroscopic parameters for SiC₂ has proved particularly challenging, and its excited vibrational levels are insufficiently populated in supersonic jet sources. However, the electronic transition responsible for the well-known blue-green Merrill-Sanford bands of SiC₂ admits Franck-Condon access to vibrational levels at least 4000 K above ground, inviting the application of stimulated emission pumping (SEP) for the observation of vibrationally excited states. SiC₂ has been efficiently generated in a jet-cooled discharge of silane and acetylene, optically pumped via the M-S bands, and fluorescence depletion SEP spectra observed for dump transitions terminating in a variety of excited vibrational levels of the ground electronic state. For known transitions within 1ν₃ and 2ν₃ (the pinwheel mode), our measurements are in generally excellent agreement (a factor of at least 5 smaller than the dump laser linewidth) with previous observations, giving us good faith in our experimental procedure; rotational analyses of previously unobserved transitions of all three vibrational modes are on-going at the time of writing, and will be discussed.

The Orion Kleinmann-Low nebula (Orion KL) is a notoriously complicated region of high-mass star formation and the closest such object to Earth. The structures within Orion KL-such as the hot core and the compact ridge-have varying chemical and physical properties, making the nebula an excellent laboratory for studying the formation and subsequent chemistry of complex organic molecules in high-mass star-forming regions. Methanol (CH₃OH) is one of the simplest complex organics and can be used as a tracer of even higher degrees of complexity as well as a probe of physical conditions in the interstellar medium. Previous interferometric observations of Orion KL have elucidated chemical differentiation and large-scale variations in the physical conditions of the nebula. We conducted observations of ¹³CH₃OH toward Orion KL with the Atacama Large Millimeter/submillimeter Array (ALMA) at angular resolutions of  ∼ 0.3^′′, complementing previous observations of Orion KL at lower resolutions that use molecules, specifically CH3OH, as a probe of the region's physical conditions. We derive velocity, temperature, and ¹³CH₃OH column density maps with a spatial resolution commensurate with circumstellar disks, allowing us to probe local variations in the nebula. The derived maps show a velocity gradient that is likely the result of gas emanating from an explosion that took place about 500 years ago. We also report substructures of increased temperatures and slight ¹³CH₃OH abundance enhancements, which may be attributed to the presence of shocked material in the nebula. Overall, our findings agree with previous observations but provide a more localized view of Orion KL, further demonstrating the utility of molecules as probes of physical structures.

Magnetic fields are thought to play a crucial role in the formation and evolution of protoplanetary disks by providing a means of angular momentum transport through the magnetorotational instability and/or magnetically driven winds. However, finding observational evidence for the presence of magnetic fields in disks has proven difficult. Zeeman splitting observations offer a way to directly measure or put upper limits on line-of-sight magnetic field strengths in astronomical sources, as the circularly polarized signal produced by Zeeman splitting depends directly on the magnetic field strength along the line of sight. We present the results of ALMA observations of the CN 2-1 line in two disks: AS 209 and V4046 Sgr. The upper limits on net line-of-sight magnetic field strengths derived from these observations and their implications for the overall disk magnetic field strength and morphology will be discussed.