Enhanced Deuterium Fractionation in Dense Interstellar Cores Resulting from Multiply Deuterated H3+

In this Letter, we present the first results from updated models of interstellar deuterium chemistry that now include all possible deuterated isotopomers of H3+. We find that in regions of high density and heavy depletion, such as prestellar cores, the inclusion of HD2+ and D3+ enhances the fractionation of ionic and neutral species significantly. Our models are the first to predict the very high atomic D/H ratios (>=0.3) necessary for grain-surface chemistry models to reproduce the high formaldehyde and methanol fractionation seen in star-forming regions.

Gas-Phase Formation of Doubly-Deuterated Species

We present the first results from a time-dependent chemical model to include a gas-phase reaction scheme for producing doubly-deuterated species. Under normal conditions the formation of these species is inefficient. However, when the effects of the freeze out of gas phase species onto grains is included in the chemistry we find that the fractionation of both singly and doubly deuterated species is enhanced. We compare the predictions from our models with recent observations of deuterated molecules in L134N and find that, contrary to previous expectations, we can reproduce the observed levels of fractionation without recourse to an active grain-surface chemistry.

Molecular abundances in the Magellanic Clouds .2. Deuterated species in the LMC

The first definite discoveries of extragalactic deuterium are reported. DCO+ has been detected in three and DCN has been measured in one star-forming region of the Large Magellanic Cloud (LMC). While the HCO+/DCO+ abundance ratios are found to be 19 +/- 3, 24 +/- 4, and 67 +/- 18 for N113, N44BC and N159HW, respectively, a HCN/DCN abundance ratio of 23 +/- 5 is obtained for N113. These results are consistent with a gas temperature of about 20 K and a D/H ratio of about 1.5 x 10(-5), consistent with that observed in the Galaxy. If the cloud temperature is closer to 30 K, then a D/H ratio is required to be up to an order of magnitude larger. Because this ratio provides a lower limit to the primordial D/H ratio, it indicates that the baryon mass density alone is unable to close the universe.

OBSERVATIONS OF DEUTERATED CYANOACETYLENE IN DARK CLOUDS

We have observed DC3N and HC3N in a number of cold dust clouds in order to derive the degree of deuterium fractionation. We find that the ratio of DC3N to HC3N is large, at about 0.05 or more, and discuss the implications of this result for the synthesis of cyanoacetylene. The observations are most readily interpreted if the deuteration of HC3N is linked to that of cyclic C3H2, which is also observed to exhibit a large degree of deuterium fractionation. HC3N deuteration levels comparable with those we observed are found to he just compatible with the mechanism suggested by Howe & Millar, but with adjusted rate coefficients. Freeze-out on to grain surfaces is also considered, but produces widespread deuterium enhancement in many species. contrary to observed levels.

A survey of [ D2CO] /[ H2CO] and [ N2D^+] /[ N2H^+] ratios towards protostellar cores

Aims.We use observations and models of molecular D/H ratios to probe the physical conditions and chemical history of the gas and to differentiate between gas-phase and grain-surface chemical processing in star forming regions. Methods: As a follow up to previous observations of HDCO/H2CO and DCN/HCN ratios in a selection of low-mass protostellar cores, we have measured D2CO/H2CO and N2D^+/N2H+ ratios in these same sources. For comparison, we have also measured N2D^+/N2H+ ratios towards several starless cores and have searched for N2D+ and deuterated formaldehyde towards hot molecular cores (HMCs) associated with high mass star formation. We compare our results with predictions from detailed chemical models, and to other observations made in these sources. Results: Towards the starless cores and low-mass protostellar sources we have found very high N2D+ fractionation, which suggests that the bulk of the gas in these regions is cold and heavily depleted. The non-detections of N2D+ in the HMCs indicate higher temperatures. We did detect HDCO towards two of the HMCs, with abundances 1-3% of H2CO. These are the first detections of deuterated formaldehyde in high mass sources since Turner (1990) measured HDCO/H2CO and D2CO/H2CO towards the Orion Compact Ridge. Figures 1-5 are only available in electronic form at http://www.aanda.org

The role of H2D+ in the deuteration of interstellar molecules

Collisions between H-3(+) and HD in molecular clouds lead to the fractionation of deuterium in H2D+ at temperatures below 20 K. In this article, we describe the chemistry of H2D+ and discuss how variations in temperature and elemental abundances affect the level of fractionation in H2D+ and other species. We describe how accretion of gas-phase molecules on to cold dust grains enhances the deuteration in several molecules including doubly deuterated molecules. Mie show that the ion-neutral drift velocities attained in slow Alfven waves can destroy H2D+ in non-thermal reactions. As a result, the degree of fractionation can be reduced and we discuss observational consequences of such a model for the dark dust cloud TMC-1.

Modelling of deuterium chemistry and its application to molecular clouds

We have developed new models of the chemistry of deuterium for investigating fractionation in interstellar molecular clouds. We have incorporated the latest information on reactions which affect deuteration, extended previous models to include S-D bonds for the first time and included the gasphase chemistry of some doubly-deuterated species. We present models for a wide range of physical parameters, including density, temperature, elemental abundances, and the freeze out of molecules on to dust grains. We discuss the detailed fractionation of particular species and show how fractionation can be used to probe the history of interstellar matter. The freeze out of molecules onto dust leads to significant enhancement in fractionation ratios and, in particular, to large fractionation in doubly-deuterated species.

Role of combination vibrations in resonant positron annihilation

Positrons can attach to molecules via vibrational Feshbach resonances, leading to very large annihilation rates. The predictions of a recent theory for this process are validated for deuterated methyl halides where all modes are dipole coupled to the incident positron. Data and analysis are presented for methanol and ethylene, demonstrating the importance of combination and overtone resonances and the ability of the theory to account for these features. The mechanism for these resonances and criteria for their occurrence as well as outstanding questions are discussed.

Rapid confirmatory method for the determination of sixteen synthetic growth promoters and bisphenol A in bovine milk using dispersive solid-phase extraction and liquid chromatography-tandem mass spectrometry

A rapid liquid chromatographic-tandem mass spectrometric (LC-MS/MS) multi-residue method for the simultaneous quantitation and identification of sixteen synthetic growth promoters and bisphenol A in bovine milk has been developed and validated. Sample preparation was straightforward, efficient and economically advantageous. Milk was extracted with acetonitrile followed by phase separation with NaCl. After centrifugation, the extract was purified by dispersive solid-phase extraction with C18 sorbent material. The compounds were analysed by reversed-phase LC-MS/MS using both positive and negative ionization and operated in multiple reaction monitoring (MRM) mode, acquiring two diagnostic product ions from each of the chosen precursor ions for unambiguous confirmation. Total chromatographic run time was less than 10 min for each sample. The method was validated at a level of 1 mu g L-1. A wide variety of deuterated internal standards were used to improve method performance. The accuracy and precision of the method were satisfactory for all analytes. The confirmative quantitative liquid chromatographic tandem mass spectrometric (LC-MS/MS) method was validated according to Commission Decision 2002/657/EC. The decision limit (CC alpha) and the detection capability (CC beta) were found to be below the chosen validation level of 1 mu g L-1 for all compounds. (C) 2010 Elsevier B.V. All rights reserved.

TiK alpha radiography of Cu-doped plastic microshell implosions via spherically bent crystal imaging

We show that short pulse laser generated Ti K alpha radiation can be used effectively as a backlighter for radiographic imaging. This method of x-ray radiography features high temporal and spatial resolution, high signal to noise ratio, and monochromatic imaging. We present here the Ti K alpha backlit images of six-beam driven spherical implosions of thin-walled 500-mu m Cu-doped deuterated plastic (CD) shells and of similar implosions with an included hollow gold cone. These radiographic results were used to define conditions for the diagnosis of fast ignition relevant electron transport within imploded Cu-doped coned CD shells. (c) 2005 American Institute of Physics.

Ion acceleration from the shock front induced by hole boring in ultraintense laser-plasma interactions

Ion-acceleration processes have been studied in ultraintense laser plasma interactions for normal incidence irradiation of solid deuterated targets via neutron spectroscopy. The experimental neutron spectra strongly suggest that the ions are preferentially accelerated radially, rather than into the bulk of the material from three-dimensional Monte Carlo fitting of the neutron spectra. Although the laser system has a 10(-7) contrast ratio, a two-dimensional magnetic hydrodynamics simulation shows that the laser pedestal generates a 10 mum scale length in the coronal plasma with a 3 mum scale-length plasma near the critical density. Two-dimensional particle-in-cell simulations, incorporating this realistic density profile, indicate that the acceleration of the ions is caused by a collisionless shock formation. This has implications for modeling energy transport in solid is caused by a collisionless shock formation. This has implications for modeling energy transport in solid density plasmas as well as cone-focused fast ignition using the next generation PW lasers currently under construction.