ASTRONOMICAL TRIPLETS: ALMA OBSERVATIONS OF C2H4O2 ISOMERS IN SGR B2 (N)

The $mathrm{C_2H_4O_2}$ triplet found in the interstellar medium (ISM) consists of glycolaldehyde ($mathrm{CH_2OHCHO}$), acetic acid ($mathrm{CH_3COOH}$) and methyl formate ($mathrm{HCOOCH_3}$). The forming mechanism of their $mathrm{HCO}$-bearing component involves both gas-phase and grain-surface processes whose relative roles plays into fundamental questions within the fields of astrochemistry and astrobiology. Glycolaldehyde is closely related to ribose and deoxyribose, the primary components of genetic materials. The first detection of Glycolaldehyde was toward Sgr B2 with using NRAO 12 m telescope in 2000 (J. M. Hollis et al). A new careful search for glycolaldehyde toward the hot dense core Sgr B2 (N) is needed. While methyl formate has a large number of detected transitions throughout the ISM, the detection of acetic acid, the least abundant of these isomers, is more tentative. Mehringer et al. (1997) reported only 4 lines of acetic acid toward Sgr B2 Large Molecule Heimat source. Here, we confirm these detections of each species toward Sgr B2 (N) with the more sensitive and larger bandwidth from ALMA Band 3 observations (A. Belloche, 2012), providing us more transitions and more accurate continuum subtraction. Based on these results, the abundances and spatial distributions of the $mathrm{C_2H_4O_2}$ triplet species would be obtained and compared

Astrochemical Modeling of Propargyl Radical Chemistry in TMC-1

Recent detections of aromatic species in dark molecular clouds suggest formation pathways may be efficient at very low temperatures and pressures, yet current astrochemical models are unable to account for their derived abundances, which can often deviate from model predictions by several orders of magnitude. The propargyl radical, a highly abundant species in the dark molecular cloud TMC- 1, is an important aromatic precursor in combustion flames and possibly interstellar environments. We performed astrochemical modeling of TMC-1 using the three-phase gas-grain code NAUTILUS and an updated chemical network, focused on refining the chemistry of the propargyl radical and related species. The abundance of the propargyl radical has been increased by half an order of magnitude compared to the previous GOTHAM network. This brings it closer in line with observations, but it remains underestimated by two orders of magnitude compared to its observed value. Predicted abundances for the chemically related C4H3N isomers within an order of magnitude of observed values corroborate the high efficiency of CN addition to closed-shell hydrocarbons under dark molecular cloud conditions. The results of our modeling provide insight into the chemical processes of the propargyl radical in dark molecular clouds and highlight the importance of resonance-stabilized radicals in PAH formation.Comment: 31 pages and 17 figures (including the appendix), accepted for publication in The Astrophysical Journa

Detection of Interstellar HC4_4NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions

We report an astronomical detection of HC$_4$NC for the first time in the interstellar medium with the Green Bank Telescope toward the TMC-1 molecular cloud with a minimum significance of $10.5 \sigma$. The total column density and excitation temperature of HC$_4$NC are determined to be $3.29^{+8.60}_{-1.20}\times 10^{11}$ cm$^{-2}$ and $6.7^{+0.3}_{-0.3}$ K, respectively, using the MCMC analysis. In addition to HC$_4$NC, HCCNC is distinctly detected whereas no clear detection of HC$_6$NC is made. We propose that the dissociative recombination of the protonated cyanopolyyne, HC$_5$NH$^+$, and the protonated isocyanopolyyne, HC$_4$NCH$^+$, are the main formation mechanisms for HC$_4$NC while its destruction is dominated by reactions with simple ions and atomic carbon. With the proposed chemical networks, the observed abundances of HC$_4$NC and HCCNC are reproduced satisfactorily.Comment: Accepted in the Astrophysical Journal Letter