Spectral line surveys of the Taurus Molecular Cloud-1 (TMC-1) have led to the detection of more than 100 new molecular species, making it the most prolific source of interstellar molecular discoveries. These wide-band, high-sensitivity line surveys have been enabled by advances in telescope and receiver technology, particularly at centimeter and millimeter wavelengths. In this work, we present a statistical analysis of the molecular inventory of TMC-1 as probed by the GOTHAM large program survey from 3.9 to 36.4 GHz. To fully unlock the potential of the ∼29 GHz spectral bandwidth, we developed an automated pipeline for data reduction and calibration. We applied a Bayesian approach with Markov Chain Monte Carlo fitting to the calibrated spectra and constrained column densities for 102 molecular species detected in TMC-1, including 75 main isotopic species, 20 carbon-13 substituted species, and seven deuterium-substituted species. This list of the detected gas-phase molecules is populated by unsaturated hydrocarbons, in stark contrast to the oxygen-rich organics found in sublimated ices around protostars. Of note, 10 individual aromatic molecules were identified in the GOTHAM observations, contributing 0.011% of the gas-phase carbon budget probed by detected molecules when including CO and 6% when excluding CO. This work provides a reference set of observed gas-phase molecular abundances for interstellar clouds, offering a new benchmark for astrochemical theoretical models.

We present the synthesis and laboratory rotational spectroscopy of the 7-ring polycyclic aromatic hydrocarbon (PAH) cyanocoronene (C_24H_11CN) using a laser-ablation assisted cavity-enhanced Fourier transform microwave spectrometer. A total of 71 transitions were measured and assigned between 6.8–10.6 GHz. Using these assignments, we searched for emission from cyanocoronene in the GBT Observations of TMC-1: Hunting Aromatic Molecules (GOTHAM) project observations of the cold dark molecular cloud TMC-1 using the 100 m Green Bank Telescope (GBT). We detect a number of individually resolved transitions in ultrasensitive X-band observations and perform a Markov Chain Monte Carlo analysis to derive best-fit parameters, including a total column density of N(C_24H_11CN) = 2.69^+0.26_-0.23× 10^12 cm^-2 at a temperature of 6.05^+0.38_-0.37K. A spectral stacking and matched filtering analysis provides a robust 17.3σ significance to the overall detection. The derived column density is comparable to that of cyano-substituted naphthalene, acenaphthylene, and pyrene, defying the trend of decreasing abundance with increasing molecular size and complexity found for carbon chains. We discuss the implications of the detection for our understanding of interstellar PAH chemistry and highlight major open questions and next steps.

We present the spectroscopic characterization of cyclopropenethione in the laboratory and detect it in space using the Green Bank Telescope Observations of TMC-1: Hunting Aromatic Molecules survey. The detection of this molecule—the missing link in understanding the C 3 H 2 S isomeric family in TMC-1—completes the detection of all three low-energy isomers of C 3 H 2 S, as both CH 2 CCS and HCCCHS have been previously detected in this source. The total column density of this molecule ( N T of 5.7 2 − 1.61 + 2.65 × 1 0 10 cm −2 at an excitation temperature of 4 . 7 − 1.1 + 1.3 K) is smaller than both CH 2 CCS and HCCCHS and follows nicely the relative dipole principle (RDP), a kinetic rule of thumb for predicting isomer abundances that suggests that, all other chemistry among a family of isomers being the same, the member with the smallest dipole ( μ ) should be the most abundant. The RDP now holds for the astronomical abundance ratios of both the S-bearing and O-bearing counterparts observed in TMC-1; however, CH 2 CCO continues to elude detection in any astronomical source.

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 SiC 2 is a known, abundant molecular constituent of this region, it is a reasonable supposition that some fraction of the observed U lines arise from vibrationally excited levels of SiC 2 populated at elevated temperatures.At present, the laboratory rotational data that would permit testing of this hypothesis are largely absent: ab initio prediction of relevant spectroscopic constants has proved particularly challenging for SiC 2 , and its excited vibrational levels are not efficiently populated in supersonic jet sources.However, the electronic transition responsible for the well-known blue-green Merrill-Sanford bands of SiC 2 admits Franck-Condon access to vibrational levels at least 4000 K above ground, inviting the application of SEP spectroscopy for the observation of vibrationally excited states.SiC 2 has been generated in our laboratory 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 rovibrational levels for all three modes in the X-state.For known rotational levels of 1ν 3 and 2ν 3 (the pinwheel mode), the rotational energies derived from SEP spectra 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.The 1ν 2 level is notably perturbed, which likely accounts for its as-yet non-observation in the laboratory by rotational spectroscopy.A Fermi resonance with 6ν 3 depresses the 1ν 2 B and C constants significantly below the predictions of high-level theory.Vibrationally averaged rotational constants calculated using Fermi resonance mixing coefficients obtained from Ã-state zero-point dispersed fluorescence are broadly consistent with this interpretation.

We present a joint laboratory, theoretical, and astronomical study of several new metal-carbon clusters including the alkaline earth metal-bearing molecules MgC 2 , CaC 2 , and SrC 2 , as well as the closely related rare earth molecule YbC 2 .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 MgC 2 and CaC 2 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 sand 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.

We report the detection of magnesium dicarbide, MgC 2 , in the laboratory at centimeter wavelengths and assign 24 MgC 2 , 25 MgC 2 , and 26 MgC 2 to 14 unidentified lines in the radio spectrum of the circumstellar envelope of the evolved carbon star IRC+10216. The structure of MgC 2 is found to be T-shaped with a highly ionic bond between the metal atom and the C 2 unit, analogous to other dicarbides containing electropositive elements. A two-temperature excitation model of the MgC 2 emission lines observed in IRC+10216 yields a very low rotational temperature of 6 ± 1 K, a kinetic temperature of 22 ± 13 K, and a column density of (1.0 ± 0.3) × 10 12 cm −2 . The abundance of MgC 2 relative to the magnesium–carbon chains MgCCH, MgC 4 H, and MgC 6 H is 1:2:22:20 and provides a new constraint on the sequential radiative association–dissociative recombination mechanisms implicated in the production of metal-bearing molecules in circumstellar environments.

Pure rotational transitions of the deuterated NH3-H-2 weakly bound complexes formed by NH3/ND3 and H-2/D-2, namely ND3-H-2, NH3-D-2 and ND3-D-2, have been detected. Three different techniques, a millimeter-wave intracavity jet OROTRON spectrometer, molecular beam Fourier transform microwave (FTMW) cavity spectrometer and the broadband chirped pulse (CP) FTMW spectrometer were used to record the spectra in the frequency range from 20 to 140 GHz. The double resonance method was additionally applied to extend the frequency range of the OROTRON spectrometer to lower and of the FTMW cavity spectrometer to higher frequencies. A search for the transitions of deuterated isotopologues and their assignments were based on the recent study of the main isotopic species NH3-H-2 [L.A. Surin et al., Astrophys. J., 838, 27 (2017)] and further confirmed by the bound state calculations presented here. The measured line positions including hyperfine splitting due to the N-14 nuclear spin of NH3/ND3 and the D nuclear spins of D-2 were analysed in order to determine the molecular parameters and structure of the deuterated NH3-H-2 complexes. This study provides an effective new probe of the intermolecular interaction between ammonia and dihydrogen, knowledge of which is important for numerical modelling of astrophysical environments. (C) 2021 Elsevier Inc. All rights reserved.

ABSTRACT Air pollutant concentrations are often higher near major roadways than in the surrounding environments owing to emissions from on-road mobile sources. In this study, we quantified the gradient in black carbon (BC) and air toxics concentrations from the I-70 freeway in the Elyria-Swansea environmental justice neighborhood in Denver, Colorado, during three measurement campaigns in 2017–2018. The average hourly upwind-downwind gradient of BC concentrations from the roadway was 500–800 ng/m3, equal to an increment of approximately 30-80% above local background levels within 180 m of the freeway. When integrated over all wind directions, the gradients were smaller, approximately 150–300 ng/m3 (~11-18%) over the course of nearly four months of measurements. No statistically significant gradient in air toxics (e.g., benzene, formaldehyde, etc.) was found, likely because the uncertainties in the mean concentrations were larger than the magnitude of the gradient (<25%). This finding is in contrast to some earlier studies in which small gradients of benzene and other VOCs were found. We estimate that sample sizes of at least 100 individual measurements would have been required to estimate mean concentrations with sufficient certainty to quantify gradients on the order of ±10% uncertainty. These gradient estimates are smaller than those found in previous studies over the past two decades; more stringent emissions standards, the local fleet age distribution, and/or the steady turnover of the vehicle fleet may be reducing the overall impact of roadway emissions on near-road communities. Implications: Gradients of near-road pollution may be declining in the near-road environment as tailpipe emissions from the vehicle fleet continue to decrease. Near-road concentration gradients of mobile source air toxics, including benzene, 1,3-butadiene, and ethylbenzene, will require higher sample sizes to quantify as emissions continue to decline.

Polycyclic Aromatic Hydrocarbons (PAHs) have long been invoked in the study of interstellar and protostellar sources, but the unambiguous identification of any single PAH has proven elusive until very recently.As a result, the formation mechanism for this important class of molecules remains poorly constrained.Here, we will discuss the dedicated and sustained effort to explore the aromatic content in the ISM at radio wavelengths with the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) survey.We will focus on the first interstellar detection of a pure PAH, indene (C 9 H 8 ), and how it fits within the context of the other recently detected cyclic molecules, including the cyanonaphthalenes (1-and 2-C 10 H 7 CN).Indene is found to be the most abundant organic ring detected in TMC-1 to date and is more abundant than predictions from astrochemical modeling with NAUTILUS by several orders of magnitude.This detection provides a new avenue of chemical inquiry where hydrocarbon abundances can now be directly compared to those of closely-related but CN-functionalized rings and creates a strong motivation to search for these species' cyano or pure ring counterparts.

Cold carbon chemistry in the interstellar medium is well-known for its efficient production of linear carbon chain

Modeling analyses were developed to evaluate near-road PM2.5 concentrations predicted by the AERMOD dispersion modeling chain under real-world conditions, and to assess the sensitivity of modeled near-road concentrations to the choice of dispersion model (AERMOD or CAL3QHCR), meteorological data, and travel data processing approach. We evaluate PM(2.5 )monitoring sites near major freeways in Indianapolis, Indiana (for 2016) and Providence, Rhode Island (for 2015-2016). The modeling analyses are built upon bottom-up estimates of temporally and spatially resolved roadway PM2.5 emissions based on traffic monitoring data and local vehicle fleet emission factors. The dispersion model simulations use local meteorological data collected at or close to the near-road monitoring sites. Predictions involved a modeling chain that included travel activity data processing, emissions modeling (MOVES and AP-42), and air quality dispersion modeling. We estimated the difference between PM2.5 concentrations at the near-road monitor and at nearby urban air quality monitoring sites (the measured near-road "increment"), and compared modeled results to the measured increments. Based on monitoring data, estimates of multi-day-averaged near-road PM2.5 increments were 0.9 + 0.6 mu g/m(3) at Indianapolis and 1.4 +/- 0.2 mu g/m(3) at Providence (where the uncertainty represents the 95% confidence interval on the mean value), and were comparable to measured PM2.5 increments at these sites in the near-road literature. Modeled roadway contributions to multi-day-averaged near-road concentrations substantially exceeded measured values based on the near-road monitoring data. The average near-road PM2.5 increment modeled with AERMOD was more than 300% (factor of four) larger than the measured increment at Indianapolis, and more than 500% (factor of six) larger than the measured increment at Providence. These biases reflect cumulative uncertainty throughout the near-road PM2.5 modeling chain. The emissions modeling component may have contributed to the modeling chain biases in two ways. First, the relative contribution of modeled non-exhaust emissions (PM2.5 brake wear, tire wear, and re-suspended road dust) compared to tailpipe exhaust emissions was higher than what has been documented in several published studies. Second, other research findings indicate that the U.S. EPA MOVES2014 model may over-predict tailpipe PM2.5 exhaust. The dispersion modeling component may have also contributed to the modeling chain biases. For example, when local meteorological data were used, AERMOD results were relatively insensitive to wind direction on a daily averaged basis; as a result, modeled concentrations exceeded measured values regardless of whether the near-road monitor was upwind or downwind of the roadway. In summary, this work provides a unique evaluation of PM2.5 concentrations predicted by the near-road modeling chain, and provides valuable information to understand potential sources of uncertainty in the near-road modeling process.

Ambient air monitoring and phone survey data were collected in three environmental justice (EJ) and three non-EJ communities in Sacramento County during winter 2016–2017 to understand the differences in air toxics and in wood smoke pollution among communities. Concentrations of six hazardous air pollutants (HAPs) and black carbon (BC) from fossil fuel (BCff) were significantly higher at EJ communities versus non-EJ communities. BC from wood burning (BCwb) was significantly higher at non-EJ communities. Correlation analysis indicated that the six HAPs were predominantly from fossil fuel combustion sources, not from wood burning. The HAPs were moderately variable across sites (coefficient of divergence (COD) range of 0.07 for carbon tetrachloride to 0.28 for m- and p-xylenes), while BCff and BCwb were highly variable (COD values of 0.46 and 0.50). The BCwb was well correlated with levoglucosan (R2 of 0.68 to 0.95), indicating that BCwb was a robust indicator for wood burning. At the two permanent monitoring sites, wood burning comprised 29–39% of the fine particulate matter (PM2.5) on nights when PM2.5 concentrations were forecasted to be high. Phone survey data were consistent with study measurements; the only significant difference in the survey results among communities were that non-EJ residents burn with indoor devices more often than EJ residents.

Transportation projects must undergo a transportation conformity hot-spot analysis if they are designated as projects of local air quality concern (POAQC). We examined particulate matter 2.5 mu m in aerodynamic diameter or smaller (PM2.5) concentrations measured in 2017 from 48 near road monitoring sites across the U.S. Annual average PM2.5 increments, the difference between near-road and background PM2.5, were between 0.1 +/- 0.2 mu g/m(3) and 2.0 +/- 0.2 mu g/m(3) for sites without noted confounding factor(s). The highest PM2.5 increment from monitors 10 or more meters from the roadway was 1.4 +/- 0.2 mu g/m(3). Using modeled national average exhaust emissions, and associated near-road contribution to PM2.5, the upper bound of 2.0 +/- 0.2 mu g/m(3) is projected to decrease 30% from 2017 to 2040, for the types of highways assessed here, assuming a roadway with 8% heavy-duty vehicles and constant traffic volumes. These results can help inform transportation conformity POAQC designations.

Benzonitrile (C 6 H 5 CN), a polar proxy for benzene (C 6 H 6 ), has the potential to serve as a highly convenient radio probe for aromatic chemistry, provided this ring can be found in other astronomical sources beyond the molecule-rich prestellar cloud TMC-1 where it was first reported by McGuire et al. (2018).Here we present 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 benzonitrile is not unique to TMC-1; rather aromatic chemistry appears to be widespread throughout the earliest stages of star formation, likely persisting at least to the initial formation of a protostar.The abundance of benzonitrile far exceeds predictions from models which well reproduce the abundances of carbon chains, such as HC 7 N, a cyanopolyyne with the same heavy atoms, indicating the chemistry responsible for planar carbon structures (as opposed to linear ones) in primordial sources is favorable but not well understood.The abundance of benzonitrile relative to carbon-chain molecules displays sizable variations between sources within the Taurus and Serpens clouds, implying the importance of physical conditions and initial elemental reservoirs of the clouds themselves.

This presentation describes the application of a miniature millimeter-wave rotational spectrometer to the detection of laser-ablation products.The laboratory experiments we present are forerunners to possible future field-or space deployments.We focus on NaCl and KCl salts, which are interesting targets at the icy moons of the outer solar system.The laser-coupled spectrometer incorporates a collisional-cooling, pulsed carrier gas beam.We leverage the small size of the spectrometer cavity to probe the ablation product signal along the beam length.We find that the volatilized species are widely dispersed in the carrier-gas.Additionally, we present centimeter-wave rotational and mass spectroscopic measurements to help characterize the laser ablation process.