Vadim V. Ilyushin

A Rigorous Attempt to Verify Interstellar Glycine

In 2003, Kuan and coworkers reported the detection of interstellar glycine (NH2CH2COOH) based on observations of 27 lines in 19 different spectral bands in one or more of the sources Sgr B2(N-LMH), Orion KL, and W51 e1/e2. They supported their detection report with rotational temperature diagrams for all three sources. In this paper we present essential criteria that can be used in a straightforward analysis technique to confirm the identity of an interstellar asymmetric rotor such as glycine. We use new laboratory measurements of glycine as a basis for applying this analysis technique, both to our previously unpublished 12 m telescope data and to the previously published Swedish-ESO Submillimetre Telescope (SEST) data of Nummelin and colleagues. We conclude that key lines necessary for an interstellar glycine identification have not yet been found. We identify some common molecular candidates that should be examined further as more likely carriers of several of the lines reported as glycine. Finally, we illustrate that a rotational temperature diagram used without the support of correct spectroscopic assignments is not a reliable tool for the identification of interstellar molecules.

Detection of Acetamide (CH3CONH2): The Largest Interstellar Molecule with a Peptide Bond

Acetamide (CH3CONH2) has been detected in emission and absorption toward the star-forming region Sagittarius B2(N) with the 100 m Green Bank Telescope (GBT) by means of four A-species and four E-species rotational transitions. All transitions have energy levels less than 10 K. The Sgr B2(N) cloud is known to have a cold halo with clumps of gas at several different velocities. Absorption features are largely characterized by local standard of rest (LSR) velocities that are typical of the two star-forming cores with systemic LSR velocities of +64 and +82 km s-1. Continuum sources embedded within the star-forming cores give rise to the absorption from the molecular gas halo surrounding the cores. Emission features are seen at an approximate intermediate LSR velocity of +73 km s-1 that characterizes the widespread molecular halo that has a spatial scale of a few arcminutes. Two low-energy transitions of formamide (HCONH 2) were also observed with the GBT toward Sagittarius B2(N) since formamide is the potential parent molecule of acetamide; both molecules are the only interstellar species with an NH2 group bound to a CO group, the so-called peptide bond, that provides the linkage for the polymerization of amino acids. While the acetamide transitions observed appear to be confined to the cold (~8 K) halo region, only the 101-0 00 transition of formamide appears to be exclusively from the cold halo; the 312-313 transition of formamide is apparently contaminated with emission from the two hot cores. The relative abundance ratio of acetamide to formamide is estimated to be in the range of ~0.1 to ~0.5 in the cold halo. The exothermic neutral-radical reaction of formamide with methylene (CH2) may account for the synthesis of interstellar acetamide in the presence of shock phenomenon in this star-forming region.

INTERSTELLAR DETECTION of METHYL ISOCYANATE CH3NCO in Sgr B2(N): A LINK from MOLECULAR CLOUDS to COMETS

A new interstellar molecule, CH3NCO (methyl isocyanate), has been detected using the 12 m telescope of the Arizona Radio Observatory (ARO). CH3NCO was identified in spectra covering 48 GHz (68–116 GHz) in the 3 mm segment of a broadband survey of Sgr B2(N). Thirty very favorable rotational lines (Ka = 0 and Ka = 1 only; Eu < 60 K) originating in five consecutive transitions (J = 8 7, 9 8, 10 9, 11 10, and 12 11) in both the A and E internal rotation species are present in this frequency range. Emission was observed at all of the predicted frequencies, with 17 lines appearing as distinct, uncontaminated spectral features, clearly showing the classic a-type, asymmetric top pattern, with ≈ 20–70 mK. The CH3NCO spectra also appear to exhibit two velocity components near VLSR ≈ 62 and 73 km s−1, both with ΔV1/2 ≈ 10 km s−1—typical of molecules such as CH2CHCN, HNCO, and HCOOCH3 in Sgr B2(N). The column density of CH3NCO in Sgr B2(N) was determined to be Ntot ≈ 2.3 × 1013 and 1.5 × 1013 cm−2 for the 62 and 73 km s−1 components, corresponding to fractional abundances, relative to H2, of f ≈ 7.6 × 10−12 and 5.0 × 10−12, respectively. CH3NCO was recently detected in volatized material from comet 67P/Churyumov–Gerasimenko by Rosettas Philae lander, with an abundance ~1.3% of water; in Sgr B2(N), CH3NCO is roughly ~0.04% of the H2O abundance.

Microwave Spectra of Molecules of Astrophysical Interest. XXVI. Acetic Acid (CH3COOH)

The microwave spectrum of acetic acid is critically reviewed and supplemented with spectral frequency calculations derived from the rotation-torsion analysis. A simultaneous analysis of the torsional ground state, vt=0, and first and second torsionally excited states, vt=1 and 2, was carried out using the so-called “rho axis method.” The primary objective of this review is to provide radio astronomers with complete spectral coverage over the 1–400 GHz range for the ground and vt=1 states, covering rotational quantum numbers J⩽30 and |Ka|⩽15.

Microwave Spectra of Molecules of Astrophysical Interest. XXV. Methylamine

The microwave spectrum of methylamine in its ground vibrational state is critically reviewed and supplemented with spectral frequency calculations derived from rotation-internal rotation-inversion analysis. The review covers the frequency range from 1 to 500 GHz and includes the transitions with rotational quantum number J from 0 to 30. The calculated frequency with uncertainty at the 95% confidence limit along with the lower state energy and line strength are presented. For J ⩽ 10 transitions and some J > 10 transitions exhibiting large hyperfine splittings, the quadrupole hyperfine structure is also tabulated.

submillimeter wave spectroscopy of acetyl isocyanate : CH3C(O)NCO

L. MARGULÈS, R. A. MOTIYENKO, Laboratoire PhLAM, UMR 8523 CNRS Université Lille 1, Villeneuve d’Ascq, France; J.-C. GUILLEMIN, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS Université de Rennes 1, Rennes, France; BELÉN TERCERO, JOSE CERNICHARO, Departamento de Astrofı́sica, Centro de Astrobiologı́a CAB, CSIC-INTA, Madrid, Spain; ATEF JABRI, ISABELLE KLEINER, Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS et Universités Paris Est et Paris Diderot, Créteil, France; V. ILYUSHIN, Radiospectrometry Department, Institute of Radio Astronomy of NASU, Kharkov, Ukraine.