To date, there exist two formation pathways of cosmic dust: the bottom-up formation route, which deals with the formation of cosmic dust from the atomic level, and the top-down formation pathway, which shows that dust and molecules can be synthesized by breaking the pre-existing large molecules and dust grains. Shock processing is one of the important energetic events that influence the dust grains' morphology and chemical compositions via sputtering, shattering, and thermal processingJones, A. P., A. G. G. M. Tielens, and D. J. Hollenbach. Astrophysical Journal v. 469, p. 740 469 (1996): 740. In PRL, Ahmedabad, we have High-Intensity Shock Tube for Astrochemistry (HISTA), to date, the only dedicated shock tube for astrochemical and astrobiological studies. Utilizing HISTA, we studied the physicochemical transformation of cosmic dust analogues such as amorphous carbonRoy, Arijit, et al. Advances in Space Research 70.8 (2022): 2571-2581. organometallics dustRoy, Arijit, et al. Monthly Notices of the Royal Astronomical Society 517.4 (2022): 4845-4855. PAHs and minerals such as olivine and SiC. The above-described cosmic dust analogues have been shock-processed up to 7300 K for 2 ms, mimicking 5.6 M (1.8 km s⁻¹) interstellar shock processing. ATR-FTIR, Raman spectroscopy and XRD are employed to investigate the chemical changes induced in the samples, while FE-SEM and HR-TEM imaging techniques are used to study the morphological changes. In this meeting, we will discuss the new results on the formation of ISM dust/minerals in an instant from the shock processing of the precursor elements.

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Footnotes:

Jones, A. P., A. G. G. M. Tielens, and D. J. Hollenbach. Astrophysical Journal v. 469, p. 740 469 (1996): 740.. Roy, Arijit, et al. Advances in Space Research 70.8 (2022): 2571-2581., Roy, Arijit, et al. Monthly Notices of the Royal Astronomical Society 517.4 (2022): 4845-4855.,

The extreme conditions of temperature, pressure, and density in interstellar clouds lead to the condensation of gas-phase atoms and molecules onto the surface of dust grains to form icy mantles, known as interstellar ices. These ices are mainly comprised of species such water, carbon monoxide, carbon dioxide, methanol, and traces of other species. The energetic processing of these ices can lead to the formation of more interstellar complex organic molecules (iCOMS) that could act as precursors of the building blocks of life on Earth. Laboratory experiments that simulate astrophysical conditions are needed to understand the chemical pathways yielding iCOMS in space. This work aims to explore the UV photolysis of interstellar ice analogs containing water-methanol-carbon monoxide mixtures at varied concentrations realistic to observed ices using the SubLIME (Sublimation Laboratory Ice Millimeter/sub-millimeter Experiment) experimental setup, which can replicate the temperature, pressure, and radiation conditions from space. The chemical properties of the ice analogs are characterized using techniques like FT-IR (Fourier-transform infrared spectroscopy), mm/submm spectroscopy, and quadrupole mass spectrometry. The final goal is to compare the spectra of the resulting experiments with the JWST spectra obtained from the first results of the Early Release Science program "Ice Age." By comparing experimental work with observations, one can elucidate the possible chemical formation pathways of iCOMS and constrain the formation mechanisms of prebiotic compounds in interstellar environments, giving us insights into whether the precursor molecules of terrestrial life could have been supplied from space. The experimental design and initial results will be presented here.

As an abundant molecule in space, methanol has been the interest of astrochemical studies for many years. To date, the focus of laboratory studies of solid methanol has been on its formation and reactivity in ice. However, when considering the structure of methanol ice, the temperature of the phase transition in particular, there are inconsistent results reported over a wide range of crystallisation temperatures from 103 to 133 K (Dounce et al., 2007; Falk & Whalley, 1961; Giuliano et al., 2014). We present a systematic study of methanol phase transition with a focus on the influence of the environment of ice formation on the infrared spectral properties. In this study, ice layers were grown in the Portable Astrochemistry Chamber (PAC) with the ability to control deposition pressure and temperature. Methanol ice samples were investigated in the range of temperatures from 98 to 130K, considering: pure methanol, methanol layers on top of amorphous and crystalline water ice, and methanol/water ice mixtures. In pure methanol, the temperature of the phase transition has been observed at 103 K upon annealing from 20K (Podgórny & Dawes, 2023). However, structural changes in both pure methanol and samples containing water are found to be sensitive to the temperature of ice formation, as seen in the infrared spectra. Differences in the spectral profiles were analysed and used as a foundation for designing a chemometric model for retrospective analysis of the ice formation, demonstrating potential applications for studies of ice thermal history and more detailed astronomy observations.

Microwave-discharge hydrogen-flow lamps (MDHL) are a source of broadband ultraviolet light ( ∼ 115-180 nm) commonly used in laboratory experiments simulating interstellar conditions. The spectral energy distribution (SED) of an MDHL varies with the specifics of its configuration, potentially accounting for disagreeing results from different experiments in the literature. To explore this relationship, we deposited 100% CO and methanol ices under cryogenic and ultrahigh vacuum conditions. We monitored the chemical composition of the ices and their sublimated products during UV irradiation and subsequent controlled warmup using infrared spectroscopy in transmission and quadrupole mass spectrometry. We performed the UV irradiation under three different configurations by varying the pressure of the hydrogen gas in the MDHL. We first benchmarked the SED via the CO photodestruction rate, which is well studied. Then we examined the impact of the MDHL configuration on the distribution of products resulting from methanol ice photolysis. We will present the results of these studies and discuss their implications for laboratory investigations of interstellar ice analogs. Future experiments will consider the impact of other parameters, such as the microwave power applied to the MDHL, and the MDHL form (F type vs T type).

To date, over 300 molecules have been detected in the interstellar medium [1]. Laboratory experiments and astrochemical models have revealed that the primary way these molecules are formed is through the energetic processing of ice dust grains [2]. Here, we report the application of a new apparatus that probes products desorbed from an energetically processed ice with broadband rotational spectroscopy. This instrument, called CPICE, combines temperature programmed desorption of ices irradiated by high-energy electrons, buffer gas cooling, and chirped-pulse detection in the mm-wave regime. This new method provides unique insight into the chemistry of ices with the structure-specific detection afforded by rotational spectroscopy, and the quantitative nature of chirped-pulse detection. Recent results describing this new technique and measurement of species formed in electron-irradiated ices will be discussed. 1. Brett A. McGuire, ApJS (2022), 259 30 2. Karin I. Öberg, Chem. Rev. (2016) 116 (17), 9631-9663

The diffuse interstellar bands (DIBs) are interstellar absorption features in the near infrared (IR) region and are observed along sight lines of stars behind diffuse interstellar clouds. There have been  ∼ 500 absorption features observed since they were first discovered over 100 years ago, but the first carrier of the DIBs wasn’t identified until 2015 as ionised buckminsterfullerene (C60+)E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature 523, 322–323 (2015). This adds weight to the hypothesis that potential carriers of the DIBs could be polyaromatic hydrocarbons (PAH)Peeters, E.; Mackie, C.; Candian, A.; Tielens, A. G. G. M. Acc. Chem. Res. 2021, 54 (8), 1921–1933. https://doi.org/10.1021/acs.accounts.0c00747. The DIBs continue to be one of the longest unsolved mysteries of astronomy and identification of the potential carriers is a multidisciplinary search that spans the globe. Recently, resonance stabilised radicals (RSRs) or neutral open-shell PAH radicals are of particular interest since the transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) happens within the UV and the near IR putting them in contention to be a DIB carrier. As well as their radical stabilisation energy making them likely survivors in the ISM. Although no RSR has been identified as a DIB carrier the product of ionising an RSR to a closed-shell cation. Closed-shell PAH cations are expected to have electronic transitions in the visible and could be potential DIB carriers, as wellLevey, Z. UNSW Sydney, PhD thesis, 2022. https://doi.org/10.26190/UNSWORKS/24387. This presentation will focus on the spectroscopy of dimethylnaphthalene radical (by loss of hydrogen) isomers and the generation of its cations to study its chemistry and as a benchmarking molecule for the method of generating closed-shell cations via resonance enhanced multiphoton ionisation. E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature 523, 322–323 (2015).. Peeters, E.; Mackie, C.; Candian, A.; Tielens, A. G. G. M. Acc. Chem. Res. 2021, 54 (8), 1921–1933. https://doi.org/10.1021/acs.accounts.0c00747.. Levey, Z. UNSW Sydney, PhD thesis, 2022. https://doi.org/10.26190/UNSWORKS/24387..

Kinetic models are widely used in astrochemistry to explain the formation and destruction processes of detected species, but require a large number of parameters. In particular, rate coefficients under interstellar conditions (ie T = 10 K) are difficult to measure and thus often estimated or extrapolated. This creates large uncertainties that are often not quantified, especially for complex organic molecules. In this talk, I will present the results of two complementary sensitivity analyses of a modern dark molecular cloud network using the NAUTILUS 3-phase code. A focus will be placed on the application of these results to aromatic species, which are consistently underproduced by astrochemical models. We find that both methods are able to identify similar key reactions for 2-ring species, consisting of a mix of aromatic reactions as well as early hydrocarbon reactions. The major rate-limiting steps to formation of 2-ring species are found to be formation of phenyl radical (C₆H₅) and its reaction with vinylacetylene (CH₂CHC₂H) as well as ring-formation of C₆H₅⁺. Our results indicate that missing pathways in the network are likely responsible for underproduction of key species. Hydrogenation of C₃H_n hydrocarbons, which may be important to ring-formation, and alternate routes to formation of naphthalene are found to be promising areas of the network for future extension and refinement.

Correct pressure broadening is essential for modelling radiative transfer in atmospheres, however data are lacking for the many exotic molecules expected in exoplanetary atmospheres. Here we explore modern machine learning methods to mass produce pressure broadening parameters for a large number of molecules in the ExoMol database. To this end, state-of-the-art machine learning models have been used to fit to existing, empirical air-broadening data from the HITRAN database. A computationally cheap method for large-scale production of pressure broadening parameters is developed, which is shown to be reasonably (69%) accurate for unseen active molecules. This method has been used to augment the previously insufficient ExoMol line broadening diet, providing air-broadening data for all ExoMol molecules, so that the ExoMol database has a full and more accurate treatment of line broadening. Suggestions are made for improved air-broadening parameters for species present in atmospheric databases. Further work is in progress to incorporate data for line broadening by other perturbative species. This should lead to a final pipeline which can provide reasonable estimates of pressure broadening for any active-perturbing molecule pair.

A number of molecules that include the methoxy functional group have been previously detected in the interstellar medium, including dimethyl ether, methyl formate, and methoxymethanol. We therefore studied the rotational spectrum of 2-methoxyethanol in several frequency regions ranging from 8.7-500 GHz. The resulting rotational parameters permitted a search for this molecule in Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protocluster NGC 6334I as well as source B of the low-mass protostellar system IRAS 16293-2422. Several rotational transitions were observed in the ALMA Band 4 data toward NGC 6334I, resulting in the first interstellar detection of 2-methoxyethanol. However, molecular signal was not observed in the data toward IRAS 16293-2422B. In this talk, we discuss the collection and analysis of the rotational spectrum, the astronomical search for this molecule, and the possible formation pathways that could result in the different observed abundances of this molecule in the two interstellar sources.

Polycyclic aromatic hydrocarbons (PAHs) are expected to be the most abundant class of organic molecules in space. Their interstellar lifecycle is not well understood, and progress is hampered by difficulties detecting individual PAH molecules. Here, we present the discovery of {CN}-functionalized pyrene, a 4-ring PAH, in the dense cloud TMC-1 using the 100-m Green Bank Telescope. We derive an abundance of 1-cyanopyrene of ~1.52 x 10¹²cm^-2, and from this estimate that the un-substituted pyrene accounts for up to 0.03-0.3% of the carbon budget in the dense interstellar medium which trace the birth sites of stars and planets. The presence of pyrene in this cold (~10K) molecular cloud agrees with its recent measurement in asteroid Ryugu where isotopic clumping suggest a cold, interstellar origin. Its abundance indicates that pyrene is an "island of stability" in interstellar PAH chemistry and suggests a potential cold molecular cloud origin of the carbon carried by PAHs that is supplied to forming planetary systems, including habitable worlds such as our own.

Despite their ubiquitous presence in the interstellar medium (ISM), the detailed formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) remain elusive, representing a major gap in our understanding of stellar evolution and associated astrophysical processes. Two common hypotheses for these formation pathways include the ‘bottom-up’ route, in which smaller species react in situ to build up complex molecules, and the ‘top-down’ formation route, which considers the breakdown of larger, inherited molecules into smaller components, including fullerenes and potentially PAHs. Bottom-up pathways are associated with formation in the cold ISM, while top-down pathways are thought to originate in warmer environments (such as circumstellar envelopes of AGB stars). To probe these two pathways, this work builds off the use of isotopic abundance ratios in tracing evolutionary phases of stellar development based on the primary and secondary products of stellar nucleosynthesis. We derive upper limits to the column densities for single 13C benzonitrile isotopologues in the Taurus Molecular Cloud (TMC-1), arriving at bounds to the 12C/13C abundance ratio for this species. We further examine the total potential enrichment when signal-averaging over all potential substituted isotopologues and comment on the robustness and potential pitfalls in such a meta-analysis. We will finally discuss the implications of these ratios on the physical conditions under which benzonitrile in TMC-1 may have been formed, as well as insights into potential precursor species to target in future observations.

The South Pole Telescope (SPT) has uncovered a population of high-redshift strongly gravitationally lensed starburst galaxies in a 2500 square degree cosmological survey. We conducted the first ALMA spectroscopic survey for a complete sample of 81 of these systems, which range from 1.8 < z < 6.9. For the past decade, we have been studying these sources in great detail with ALMA in ionized carbon (C+), carbon monoxide (CO), and water (H₂O)(among others). Recently, we have been conducting observations of these sources with JWST targeting H-α, Pa-α, and PAH lines. I will present an overview, highlights, and the latest results from our observation programs with ALMA and JWST and discuss the prospects for the future.