We present the fifth release of the UMIST Database for Astrochemistry (UDfA). The new reaction network contains 6173 gas-phase reactions, involving 467 species, 47 of which are new to this release. We have updated rate coefficients across all reaction types. We have included 1171 new anion reactions and updated and reviewed all photorates. In addition to the usual reaction network, we also now include, for download, state-specific deuterated rate coefficients, deuterium exchange reactions and a list of surface binding energies for many neutral species. Where possible, we have referenced the original source of all new and existing data. We have tested the main reaction network using a dark cloud model and a carbon-rich circumstellar envelope model. We present and briefly discuss the results of these models.

/pdf/the-umist-database-for-astrochemistry-2012-29l3ep98yt.pdf

The UMIST database for astrochemistry 2012

Extraterrestrial abiotic amino acids and hydrocarbons in type II carbonaceous chondrite at Murchison, Australia

Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite.

▪ Abstract The physical conditions in molecular clouds control the nature and rate of star formation, with consequences for planet formation and galaxy evolution. The focus of this review is on the...

Physical conditions in regions of star formation

Recent advances in the understanding of the chemical processes that occur during all stages of the formation of stars, from the collapse of molecular clouds to the assemblage of icy planetesimals in protoplanetary accretion disks, are reviewed. Observational studies of the circumstellar material within 100‐10,000 AU of the young star with (sub)millimeter single-dish telescopes, millimeter interferometers, and ground-based as well as space-borne infrared observatories have only become possible within the past few years. Results are compared with detailed chemical models that emphasize the coupling of gas-phase and grain-surface chemistry. Molecules that are particularly sensitive to different routes of formation and that may be useful in distinguishing between a variety of environments and histories are outlined. In the cold, low-density prestellar cores, radicals and long unsaturated carbon chains are enhanced. During the cold collapse phase, most species freeze out onto the grains in the high-density inner region. Once young stars ignite, their surroundings are heated through radiation and/or shocks, whereupon new chemical characteristics appear. Evaporation of ices drives a “hot core” chemistry rich in organic molecules, whereas shocks propagating through the dense envelope release both refractory and volatile grain material, resulting in prominent SiO, OH, and H2O emission. The role of future instrumentation in further developing these chemical and temporal diagnostics is discussed.

/pdf/chemical-evolution-of-star-forming-regions-2j830kxyvn.pdf

Chemical evolution of star-forming regions

Interstellar formaldehyde (${\mathrm{H}}_{2}$CO) has been detected in absorption against numerous galactic and extragalactic radio sources by means of the ${1}_{11}$-${1}_{10}$ ground-state rotational transition at 4830 MHz. The absorbing regions often correspond in velocity with 18-cm OH features. ${\mathrm{H}}_{2}$CO is the first organic polyatomic molecule ever detected in the interstellar medium and its widespread distribution indicates that processes of interstellar chemical evolution may be much more complex than previously assumed.

Microwave Detection of Interstellar Formaldehyde

Observations of Radio Emission from Interstellar Hydrogen Cyanide

Interstellar Isocyanic Acid

Formaldehyde Absorption in Dark Nebulae

Interstellar cyanoallene (CH2CCHCN) has been detected with the 100 m Green Bank Telescope (GBT) toward the dark Taurus molecular cloud (TMC-1) by means of the 414-313, 404-303, 515-414, and 505-404 rotational transitions at 20.2, 20.6, 25.2, and 25.7 GHz, respectively. The hyperfine structure (hfs) of the 414-313 transition is resolved; the remaining transitions have hfs components that are blended but are inferred owing to line width excesses atypical of TMC-1. An analysis of these four rotational transitions yields an average column density NT = 2.0(5) × 1012 cm-2 at an assumed rotational temperature of 4 K. The cyanoallene isomer methylcyanoacetylene (CH3CCCN) has previously been observed in TMC-1 and found to have a rotational temperature of ~4 K by other investigators. Using the GBT, the K = 0 and K = 1 structure of the JK = 5K-4K transition of methylcyanoacetylene was resolved toward TMC-1 and a total column density of NT = 4.5(4) × 1011 cm-2 was obtained for the 4 K rotational temperature. Thus, cyanoallene appears to be more abundant than methylcyanoacetylene toward TMC-1 by a factor of ~4.5. The implications of this result are discussed in terms of relative bonding energy differences and possible differences in formation chemistry.

https://iopscience.iop.org/article/10.1086/500431/pdf

Lewis E. Snyder

Papers

Microwave Detection of Interstellar Formaldehyde

Observations of Radio Emission from Interstellar Hydrogen Cyanide

Interstellar Isocyanic Acid

Formaldehyde Absorption in Dark Nebulae

Hyperfine Structure Identification of Interstellar Cyanoallene toward TMC-1