Formation of benzene in the interstellar medium.

Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block--the aromatic benzene molecule--has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C(6)H(6)) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C(2)H + H(2)CCHCHCH(2) → C(6)H(6) + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering.

Unidentified infrared emission bands are ubiquitous in many astronomical sources. These bands are widely, if not unanimously, attributed to collective emissions from polycyclic aromatic hydrocarbon (PAH) molecules, yet no single species of this class has been identified in space. Using spectral matched filtering of radio data from the Green Bank Telescope, we detected two nitrile-group-functionalized PAHs, 1- and 2-cyanonaphthalene, in the interstellar medium. Both bicyclic ring molecules were observed in the TMC-1 molecular cloud. In this paper, we discuss potential in situ gas-phase PAH formation pathways from smaller organic precursor molecules.

Qualitative, exploratory pilot study to investigate how people living with posterior cortical atrophy, their carers and clinicians experience tests used to assess vision.

OBJECTIVES: To investigate the experiences and views of people living with posterior cortical atrophy (PCA), their family carers and healthcare professionals of vision assessment tests. DESIGN: A qualitative investigation using video recordings of vision assessments, semistructured interviews and audio recordings of a focus group. Interviews and focus group used broad, open questions around the topic to prompt and guide discussion. Video and audio recordings were transcribed, manually coded and analysed using framework analysis. SETTING: University College, London's Queen Square neurology centre provided the venues for all stages of the research. PARTICIPANTS: Participants living with PCA were one male and two females (age range 67-78 years). Health professional participants were a neurologist (male), two ophthalmologists (male) and an optometrist (female). PRIMARY AND SECONDARY OUTCOMES: (1) Experiences and attitudes of people living with PCA and health professionals to vision assessment tests, (2) views of health professionals and people living with PCA of whether some tests are more effective at discriminating between cortical vision problems and vision problems related to optical or ocular causes. RESULTS: Patients were able to engage with and complete a number of tests. Their partners played a vital role in the process. Participants reported that simple, short tests were more effective than more subjective tests. Examples of tests that appeared to be more problematic for the patient participants were the Amsler Grid and visual field analysis. CONCLUSIONS: Although limited in scope and execution, the project suggests that some vision assessment tests are likely to support health professionals to discriminate between cortical and optical/ocular causes of visual impairment. It supports existing evidence that there are vision assessments that people with dementia can engage with and complete. We identify areas of importance for future research and make tentative suggestions for clinical practice.

ALMA detection and astrobiological potential of vinyl cyanide on Titan.

Recent simulations have indicated that vinyl cyanide is the best candidate molecule for the formation of cell membranes/vesicle structures in Titan's hydrocarbon-rich lakes and seas. Although the existence of vinyl cyanide (C2H3CN) on Titan was previously inferred using Cassini mass spectrometry, a definitive detection has been lacking until now. We report the first spectroscopic detection of vinyl cyanide in Titan's atmosphere, obtained using archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), collected from February to May 2014. We detect the three strongest rotational lines of C2H3CN in the frequency range of 230 to 232 GHz, each with >4σ confidence. Radiative transfer modeling suggests that most of the C2H3CN emission originates at altitudes of ≳200 km, in agreement with recent photochemical models. The vertical column densities implied by our best-fitting models lie in the range of 3.7 × 1013 to 1.4 × 1014 cm-2. The corresponding production rate of vinyl cyanide and its saturation mole fraction imply the availability of sufficient dissolved material to form ~107 cell membranes/cm3 in Titan's sea Ligeia Mare.

The ESO Diffuse Interstellar Bands Large Exploration Survey: EDIBLES I. Project description, survey sample and quality assessment.

The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the [Formula: see text] fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectral type stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution (R ~ 70 000 - 100 000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305-1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided.

Small-scale-structure of the interstellar medium probed through diffuse band observations.

The carriers of the diffuse interstellar band spectrum represent an important baryonic component of the interstellar medium (ISM) and it is expected that their identification will contribute significantly to the understanding of the chemistry and physics of interstellar clouds. It is widely held that the carriers are linked to the presence of dust grains on account of the good correlation of their strengths with interstellar reddening, so they offer an important potential route to improving our understanding of the composition and chemistry of grains and grain surfaces. In addition to the challenge of making the spectral assignments, an important current question concerns the spatial distribution and physical state of interstellar material, with recent observational atomic and molecular line absorption studies suggesting that diffuse clouds are more 'clumpy' than previously thought. We describe here high signal-to-noise optical observations made at the Anglo-Australian Telescope using UCLES that were undertaken to investigate the spatial distribution of diffuse band carriers. We describe the first detection of 'small-scale-structure' in the diffuse band carrier distribution in the ISM, and comment on the possibilities that these data hold for contributing to the solution of the diffuse band problem and our understanding of the nature of small-scale-structure in the diffuse ISM.