On 31 March 1969, the era of modern radio astrochemistry started with the detection of interstellar formaldehyde (H 2 CO).It was the first detection at radio wavelengths of a molecule with more than one heavy atom (previous detections up until this discovery were limited to hydrogen atoms attached to a single heavy atom, e.g.CH, OH or NH 3 ) and, with the improvements in radio frequency receivers and new astronomical facilities coming online, heralded an era of discovery that has lasted for now more than 50 years.During this time, the number of new molecule detections has remained nearly constant at 3.7 molecules/year with a vast majority of these discoveries taking place in the radio regime (McGuire, B. 2018, APJS, 239, 17).This presentation will take us back to the time of this first detection, a quick synopsis of how observations of formaldehyde has led to a better understanding of the physical and chemical environments of astronomical sources and finally a look to the future with recent Green Bank Telescope (GBT) and Karl G. Jansky Very Large Array (VLA) observations of the 4830 MHz transition and high frequency searches with the Atacama Large Millimeter/submillimeter Array (ALMA).

In this paper, we present the results of an observational search for gas phase urea [(NH2)2CO] observed toward the Sgr B2(N-LMH) region. We show data covering urea transitions from ∼100 GHz to 250 GHz from five different observational facilities: the Berkeley–Illinois–Maryland-Association (BIMA) Array, the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the NRAO 12 m telescope, the IRAM 30 m telescope, and the Swedish-ESO Submillimeter Telescope (SEST). The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best-fit column density, temperature, and source size parameters which vary by less than a factor of two between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity of both (NH2)2CO and of Sgr B2(N) makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.

Acetic acid (CH$_3$COOH) has been detected mainly in hot molecular cores where the distribution between oxygen (O) and nitrogen (N) containing molecular species is co-spatial within the telescope beam. Previous work has presumed that similar cores with co-spatial O and N species may be an indicator for detecting acetic acid. However, does this presumption hold as higher spatial resolution observations become available of large O and N-containing molecules? As the number of detected acetic acid sources is still low, more observations are needed to support this postulate. In this paper, we report the first acetic acid survey conducted with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 3 mm wavelengths towards G19.61-0.23, G29.96-0.02 and IRAS 16293-2422. We have successfully detected CH$_3$COOH via two transitions toward G19.61-0.23 and tentatively confirmed the detection toward IRAS 16293-2422 A. The determined column density of CH$_3$COOH is 2.0(1.0)$\times 10^{16}$ cm$^{-2}$ and the abundance ratio of CH$_3$COOH to methyl formate (HCOOCH$_3$) is 2.2(0.1)$\times 10^{-1}$ toward G19.61-0.23. Toward IRAS 16293 A, the determined column density of CH$_3$COOH is $\sim$ 1.6 $\times 10^{15}$ cm$^{-2}$ and the abundance ratio of CH$_3$COOH to methyl formate (HCOOCH$_3$) is $\sim$ 1.0 $\times 10^{-1}$ both of which are consistent with abundance ratios determined toward other hot cores. Finally, we model all known line emission in our passband to determine physical conditions in the regions and introduce a new metric to better reveal weak spectral features that are blended with stronger lines or that may be near the 1-2$\sigma$ detection limit.

Author Institution: Department of Astronomy, University of Illinois at Urbana-Champaign; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana IL 61801; NRAO, Charlottesville VA 22903; Optical Technology Division, NIST, Gaithersburg MD 20899-8441; NASA/GSFC, Code 606, Greenbelt MD 20771

We present observations of HCN J = 1–0 and CH3OH J(Ka, Kc) = 3(1, 3)–4(0, 4) A+ emission from comet C/2002 T7 (LINEAR) obtained simultaneously with the Owens Valley Radio Observatory (OVRO) and Berkeley–Illinois–Maryland Association (BIMA) millimeter interferometers. We combined the data from both arrays to increase the (u, v) sampling and signal to noise of the detected line emission. We also report the detection of CH3OH J(Ka, Kc) = 8(0, 8)–7(1, 7) A+ with OVRO data alone. Using a molecular excitation code that includes the effects of collisions with water and electrons, as well as pumping by the Solar infrared photons (for HCN alone), we find a production rate of HCN of 2.9 × 1026 s−1 and for CH3OH of 2.2 × 1027 s−1. Compared to the adopted water production rate of 3 × 1029 s−1, this corresponds to an HCN/H2O ratio of 0.1% and a CH3OH/H2O ratio of 0.7%. We critically assess the uncertainty of these values due to the noise (∼10%), the uncertainties in the adopted comet model (∼50%), and the uncertainties in the adopted collisional excitation rates (up to a factor of 2). Pumping by Solar infrared photons is found to be a minor effect for HCN, because our 15″ synthesized beam is dominated by the region in the coma where collisions dominate. Since the uncertainties in the derived production rates are at least as large as one-third of the differences found between comets, we conclude that reliable collision rates and an accurate comet model are essential. Because the collisionally dominated region critically depends on the water production rate, using the same approximate method for different comets may introduce biases in the derived production rates. Multiline observations that directly constrain the molecular excitation provide much more reliable production rates.

Author Institution: Department of Astronomy, University of Illinois at Urbana-Champaign; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana IL 61801; NRAO, Charlottesville VA 22903; Optical Technology Division, NIST, Gaithersburg MD 20899-8441; NASA/GSFC, Code 606, Greenbelt MD 20771

Author Institution: Department of Astronomy, University of Illinois; at Urbana-Champaign, IL 61801; National Radio Astronomy Observatory, Charlottesville, VA 22903

We present an interferometric and single-dish study of small organic species toward Comets C/1995 O1 (Hale-Bopp) and C/2002 T7 (LINEAR) using the BIMA interferometer at 3 mm and the ARO 12 m telescope at 2 mm. For Comet Hale-Bopp, both the single-dish and interferometer observations of CH3OH indicate an excitation temperature of 105 +/- 5 K and an average production rate ratio Q(CH3OH)/Q(H2O) similar to 1.3% at similar to 1 AU. In addition, the aperture synthesis observations of CH3OH suggest a distribution well described by a spherical outflow and no evidence of significant extended emission. Single-dish observations of CH3CN in Comet Hale-Bopp indicate an excitation temperature of 200 +/- 10 K and a production rate ratio of Q(CH3CN)/Q(H2O) similar to 0.017% at similar to 1 AU. The nondetection of a previously claimed transition of cometary (CH2OH)(2) toward Comet Hale-Bopp with the 12 m telescope indicates a compact distribution of emission, D < 9 '' (< 8500 km). For the single-dish observations of Comet T7 LINEAR, we find an excitation temperature of CH3OH of 35 +/- 5 K and a CH3OH production rate ratio of Q(CH3OH)/Q(H2O) similar to 1.5% at similar to 0.3 AU. Our data support current chemical models that CH3OH, CH3CN, and (CH2OH)(2) are parent nuclear species distributed into the coma via direct sublimation off cometary ices from the nucleus with no evidence of significant production in the outer coma.

We present high-resolution Combined Array for Research in Millimeter-Wave Astronomy (CARMA) λ = 1 mm observations of several molecular species toward Orion-KL. These are the highest spatial and spectral resolution 1 mm observations of these molecules to date. Our observations show that ethyl cyanide [C2H5CN] and vinyl cyanide [C2H3CN] originate from multiple cores near the Orion hot core and IRc7. In addition we show that dimethyl ether [(CH3)2O] and methyl formate [HCOOCH3] originate from IRc5 and IRc6 and that acetone [(CH3)2CO] originates only from areas where both N-bearing and O-bearing species are present.

Author Institution: Department of Astronomy, University of Illinois at Urbana-Champaign; Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign, Urbana IL 61801; NRAO, Charlottesville VA 22903; Optical Technology Division, NIST, Gaithersburg MD 20899-8441; NASA/GSFC, Code 606, Greenbelt MD 20771

We present high resolution, Combined Array for Research in Millimeter-Wave Astronomy (CARMA), $λ$=1mm observations of several molecular species toward Orion-KL. These are the highest spatial and spectral resolution 1mm observations of these molecules to date. Our observations show that ethyl cyanide [C$_2$H$_5$CN] and vinyl cyanide [C$_2$H$_3$CN] originate from multiple cores near the Orion hot core and IRc7. Additionally we show that dimethyl ether [(CH$_3$)$_2$O] and methyl formate [HCOOCH$_3$] originate from IRc5 and IRc6 and that acetone [(CH$_3$)$_2$CO] originates only from areas where both N-bearing and O-bearing species are present.

Author Institution: Department of Astronomy, University of Illinois, Urbana, IL; National Radio Astronomy Observatory, Charlottesville, VA

Author Institution: Department of Astronomy, University of Illinois at Urbana-Champaign, IL 61801; National Radio Astronomy Observatory, Charlottesville, VA 22903; Department of Astronomy, University of Illinois at Urbana-Champaign, IL 61801

Observations of formaldehyde (H2CO) have been conducted toward comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H2CO at 3 mm were made using the Berkeley-Illinois-Maryland Association (BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H2CO is ~3.7 × 1028 s-1 at ~1 AU in comet Hale-Bopp, using a simple Monte Carlo model, if a nuclear origin for the molecule is assumed. However, maps of H2CO in Hale-Bopp, in comparison with CO, show an extended distribution (rs ~ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H2CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H2CO increases to Q ~ 1.4 × 1029 s-1 assuming such an extended grain source. This value implies a Q/Q(H2O) ~ 1.4%, which is similar to the production rate ratio of Q/Q(H2O) ~ 4% derived from in situ measurements of H2CO in comet Halley. Production rates for H2CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 (NEAT) are 1.4 × 1027 and 5.6 × 1026 s-1, respectively, modeled using the extended grain source. The spectra of H2CO measured toward comet C/2002 T7 (LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation.