While molecular hydrogen is by far the most abundant gas phase molecule in interstellar dark clouds,

The high abundance of condensed phase CO in cool quiescent molecular clouds is not reproducible by our standard two-phase and three-phase gas-grain chemical models. We consider changes to the models designed the enhance the predicted abundance of condensed phase CO. We find that the use of the so-called ...

Comets and the relative abundance of molecules in the gas phase in interstellar clouds are investigated. The justification for a joint treatment lies in the possibility that comets may consist of a frozen matrix of interstellar volatiles and grains formed during the early stages of the collapse of the molecular cloud which ultimately ...

There is observational evidence that nuclear winds and X-rays can heavily influence the physical conditions and chemical abundances of molecular gas in the circumnuclear disks (CND) of Active Galactic Nuclei (AGN). In this paper we probe the chemical status of molecular gas in the CND of ...

There is observational evidence that nuclear winds and X-rays can heavily influence the physical conditions and chemical abundances of molecular gas in the circumnuclear disks (CND) of Active Galactic Nuclei (AGN). In this paper we probe the chemical status of molecular gas in the CND of NGC ...

Context. Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the ...

Dark cloud chemical models usually predict large amounts of O2, often above observational limits. We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the ...

Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the ...

The gas phase chemistry of hot molecular cores is thought to depend upon the composition of evaporated ice mantle material and its subsequent gas phase reactions. We have modelled the silicon chemistry in these conditions from an SiH4 precursor and find substantial fractional abundances of SiO, H2SiO and HNSi on a ...

Two models of the time dependent chemical evolution of stable dense and translucent clouds are presented: one for pure gas phase chemistry and the other in which solid grain chemistry is included along with the gas. Comparing the results using these two schemes for the theoretical abundances of certain key molecules shows that ...

The paper reviews the chemical composition of gases in the coma of Comet Halley obtained from in situ and remote observations. Water vapor with an abundance of about 80 percent by number is found to be the dominant parent gas. Carbon monoxide is the second most abundant molecule, with about one-seventh of the water ...

To study the origin of the large abundances of complex organic molecules in the Galactic center (GC), we have carried out a systematic study of the complex organic molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO and CS toward 40 GC molecular clouds. Using the LTE approximation, we have derived the physical properties of GC ...

... isotopic abundance of each molecular species on the database. 3.15 Module BD-QT ... The isotopic abundance program was ...

Oxygen is the third most abundant element in the cosmos. In the gas phase, oxygen can be ionized, atomic, or in molecular, and it is also incorporated into interstellar grains. Models of the gas-phase chemistry in dense clouds predict molecular oxygen (O2) to be almost as ...

Oxygen is the third most abundant element in the cosmos. In the gas phase, oxygen can be ionized, atomic, or in molecular, and it is also incorporated into grains. Gas-phase chemistry models predict molecular oxygen (O2) to be almost as abundant as carbon monoxide (CO). A ...

We present results of a high-resolution wide-field mapping observation of Central Molecular Zone (CMZ) in SiO v=0, J=2-1 and H13CO+ J=1-0 emission lines using the Nobeyama Radio Observatory 45-m telescope and the 25-beam receiver of 100 GHz band in order to explore molecular gas affected by shock in the regions and depict the ...

We report high angular resolution observations of CN, SO, and HCN toward the reflection nebula NGC 2023. The CN data reveal the existence of high-density gas (n greater than 105/cu cm) close to the illuminating star (approximately less than or equal to 0.13 pc) which is not detected in HCN or SO. Since the spatial distribution of the dense gas is similar ...

... Title : ABUNDANCES OF ELEMENTS IN STARS AND NEBULAE (DETERMINATION OF RATIO OF GAS PRESSURE TOELECTRON PRESSURE ...

ISOCAM brought striking images of star forming regions but, thanks to its high sensitivity, it also allowed the observation of diffuse interstellar regions. Such observations allow the study of the life cycle of dust even in the diffuse ISM, and particularly through the transition from atomic to molecular gas. In this contribution we report on ...

We present an observational study of the abundance ratio of the cyclic and linear forms of the C3H2 hydrocarbon across the Photo-Dominated Region (PDR) of the Horsehead nebula. The study of this ratio is of particular interest as models predict a strong dependence of the ratio with the electronic abundance. Using the IRAM 30-m and the Effelsberg 100-m ...

The heating of the interstellar medium by photoelectric emission from large molecules or small grains is explored. Photodetachment of large negative ions may be a significant heat source in diffuse clouds. For an abundance of large molecules relative to hydrogen greater than 2 x 10 to the -7th, the heating rate from the photoelectrons produced in the photoionization of large ...

We consider four-aspects of interstellar chemistry for comparison with comets: molecular abundances in general, relative abundances of isomers (specifically, HCN and HNC), ortho/para ratios for molecules, and isotopic fractionation, particularly for the ratio hydrogen/deuterium. Since the environment in which the solar system formed is ...

The first stars in the Universe are predicted to have been much more massive than the Sun. Gravitational condensation accompanied by cooling of the primordial gas due to molecular hydrogen, yields a minimum fragmentation scale of a few hundred solar masses. Numerical simulations indicate that once a gas clump acquires this mass, it ...

We have studied how the active nucleus of the Seyfert 2 galaxy NGC 1068 influences the chemistry of its 200 pc circumnuclear disk of molecular gas (CND). Results from new observations made with the IRAM 30m telescope have served for deriving abundances of molecular species such as SiO, CN, HCO+, HOC+, H13CO+ and ...

The physical and chemical processes that operate in the cooling gas behind a fast, dissociative, single-fluid shock propagating in a dense interstellar cloud are discussed. The treatment extends previous theoretical work on fast molecular shocks by including the effects of the conversion of Ly-alpha photons into radiation of the two-photon continuum and ...

The physical and chemical processes that operate in the cooling gas behind a fast, dissociative, single-fluid shock propagating in a dense interstellar cloud are discussed. The treatment extends previous theoretical work on fast molecular shocks by including the effects of the conversion of Ly-alpha photons into radiation of the two-photon continuum and ...

Recent experimental studies of coherent anti-Stokes Raman scattering (CARS) processes in gases are beginning to define the usefulness of ths nonlinear spectroscopic technique for quantitative gas analysis. The CARS process involves the generation of a coherent light beam at an anti-Stokes Raman frequency of the material under investigation. The CARS technique may be used to ...

The emission from atoms and molecules provide our best probes into astronomical environments. Observations of atomic and molecular lines provide information on the abundance of species, the gas temperature and density. When combined with astrochemical models one may infer ionization rates along with heating and cooling rates. This ...

We have carried out a systematic study of CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO and CS in different Galactic Center (GC) molecular clouds. Figure 1 shows the relative abundances of those molecules with respect to CH3OH in the GC as function of the CH3OH abundance. The CH3OH abundance between sources ...

The Galactic center (GC) offers an unique opportunity to study in detail the processes which dominate the heating and the chemistry of the molecular gas in galactic nuclei. Within ~200 pc of the dynamical center of the Galaxy, in the molecular zone, there are a variety of very energetic phenomena like Supernovae, non-thermal ...

of carbon- ate nodules, oil and gas pockets, and biogenic debris. Sed- iment cores from the area contained and Scre- aton, 1998) and have been associated with high thermal gra- dients (Henry et al., 1996), shallow gas hydrates (Ginsburg et al., 1999), and an abundance of high-molecular weight hy- drocarbons

Initial Results from the Herschel Oxygen Project (HOP) Oxygen is the third most abundant element in the cosmos, but can be found in many forms. In the gas phase, oxygen can be ionized, atomic, or in molecular form, and it is also incorporated into grains. The molecular form is expected to dominate in cold, ...

The stability of interstellar clouds against gravitational collapse and fragmentation in the presence of magnetic fields is investigated. A magnetic field can provide pressure support against collapse if it is strongly coupled to the neutral gas; this coupling is mediated by ion-neutral collisions in the gas. The time scale for the growth of perturbations ...

This paper presents the first substantial study of the chemistry of the envelopes around a sample of 18 low-mass pre- and protostellar objects for which physical properties have previously been derived from radiative transfer modeling of their dust continuum emission. Single-dish line observations of 24 transitions of 9 molecular species (not counting isotopes) including HCO+, ...

Water continues to be one of the more compelling molecules for astronomers, despite the difficulties associated with its (non-masing) detection other than from space. Water forms in the gas-phase and on grains in ways that produce a large number of other molecules, thus making the distribution and abundance of water a very useful probe of our ...

We model the spatial dependence of molecular abundances in the accretion disk of NGC 1068, a typical AGN-dominant galaxy. A number of different possible disk structures are used, and X-rays, cosmic-rays, and UV-photons are included in the model. The effects of these parameters on molecular abundances are examined ...

We present the results of a survey of 48 molecular cloud cores and a large map covering over 100 square degrees of the Taurus Molecular Cloud Complex in cold HI absorption as well as 12CO and 13CO emission. Using a new technique developed for detecting and analyzing HI Narrow Self-Absorption (HINSA) features caused by cold HI gas ...

Context. Complex molecules such as ethanol and dimethyl ether have been observed in a number of hot molecular cores and hot corinos. Attempts to model the molecular formation process using gas phase only models have so far been unsuccessful. Aims: To demonstrate that grain surface processing is a viable mechanism for complex molecule ...

Observations made of the atomic carbon line at 492 GHz toward OMC-1 show no evidence for the high velocity dispersion wings observed for many molecular rotational lines. The 3sigma upper limit to the CI column density, NCI, is 6.9 x 10 to the 17th per sq cm for velocities greater than or equal to 4 km per sec from the line center. This upper limit corresponds to a ratio of CI ...

Interpretation of the volatile abundances in Halley's comet in terms of models for chemical and physical processes in the solar nebula are discussed. Key ratios of the oxidized and reduced species of nitrogen and carbon are identified which tell something of the chemical history of the environment in which cometary grains accreted to form the nucleus. Isotopic ...

QUE 99177 and MET 00426 are the first known CR3 chondrites and have largely escaped the aqueous alteration experienced by most of the CR chondrite group. In addition to high presolar silicate and oxide grain abundances, these meteorites also contain high abundances of phases with anomalous C isotopic compositions. Presolar SiC ...

Molecular and atomic abundances are examined for 19 lines of sight through dense clouds, each with a

Observations of high-excitation molecular emission lines can greatly increase our understanding of AGB winds, as they trace the innermost regions of the circumstellar envelope. PACS, an IR instrument on the Herschel space telescope, provides for the first time the resolution and sensitivity necessary to trace these high excitation emission lines. Specifically, we report on the ...

We investigate the evolution of molecular abundances in a protoplanetary disk in which matter is accreting toward the central star by solving numerically the reaction equations of molecules as an initial-value problem. We obtain the abundances of molecules, both in the gas phase and in ice mantles of grains, as ...

We report on the first results of an in depth study of the molecular gas properties in three high-redshift sources: IRAS FSC 10214 (z = 2.3), SMMJ14011+0252 (z = 2.5) and H1413+117 (Cloverleaf quasar, z = 2.5). Our analysis is based on observations at the IRAM interferometer and the IRAM 30m telescope of atomic carbon and multiple CO lines. Our study shows ...

In this work, we present our molecular line data for southern infrared dark clouds (IRDCs) and the first results of chemical modeling for these objects. Using the 22-m Mopra radio telescope, we performed observations toward 15 IRDCs in 13 molecular species. Where possible, we calculated molecular abundances. We ...

Molecular gas in other galaxies is generally studied by observations of CO emission; a conversion from CO integrated intensity to H/sub 2/ column density must be made. Modeling of the emission from an ensemble of molecular clouds shows that these conversion factors are sensitive to temperature, so that molecular ...

Analytic solutions to the rate equations describing the species evolution of a multispecies positive ion beam of hydrogen due to charge exchange and molecular dissociation are derived as a function of the background gas (H/sub 2/) line density in the neutralizing gas cell and in the drift tube. Using the solutions, calculations are ...

An important problem in mass isotopomer abundance mass spectrometry (MIAMS) is the dependence of measured mass isotopomer abundances on sample concentration. We have evaluated the role of ionization energy on mass isotopomer abundance ratios of methyl palmitate as a function of sample concentration. Ionization energy was varied using ...

This review considers two distinct subjects: comets, and the relative abundance of molecules in the gas phase in interstellar clouds. The justification for a joint treatment lies in the possibility that comets may consist of a frozen matrix of interstellar volatiles and grains, formed during the early stages of the collapse of the ...

Context: Far-UV photons (FUV) strongly affect the physical and chemical state of molecular gas in the vicinity of young massive stars. Aims: Finding molecular tracers of the presence of FUV radiation fields in the millimeter wavelength domain is desirable because IR diagnostics (for instance PAHs) are not easily accessible along high ...

The consequences of the Auger effect on the population of heavy-element ions are analyzed for the case of relatively cool gas irradiated by keV X-rays with intended applications to the accretion disks of young stellar objects. Highly charged ions are rapidly reduced to the doubly charged state in neutral gas, so the aim here is to derive the production ...

The detection of NH3 inversion lines up to the (J,K)=(6, 6) level is reported toward the central regions of the nearby galaxies NGC 253, Maffei 2, and IC 342. The observed lines are up to 406 K (for (J,K)=(6, 6)) and 848 K (for the (9, 9) transition) above the ground state and reveal a warm (Tkin= 100 ... 140 K) molecular component toward all galaxies studied. The tentatively ...

We report the detection of several metals in atomic form in the gas phase of the envelope of IRC+10216, the archetype of evolved carbon-rich AGB stars.By observing with VLT-UVES a background star located behind the envelope at 35 arcsec from center, optical absorption lines of Na, K, Ca, Fe and Cr are revealed. It is the first time that circumstellar Fe is detected in a ...

Context: Oxygen is the third most abundant element in the universe, but its chemistry in the interstellar medium is still not understood well. Aims: To critically examine the entire oxygen budget, we initially attempt to estimate the abundance of atomic oxygen, O, in the only region where molecular oxygen, O{2}, has been detected to ...

We consider the case of methanol production in cold dark clouds, also known as quiescent cores, for which recent work shows that a purely gas-phase synthesis is unlikely to produce a sufficient amount to explain the observational fractional abundance of approximately 10(-9). Moreover, recent experiments appear to confirm a previous hypothesis that methanol ...

We present high-resolution VLA observations of the molecular gas in the host galaxy of the highest redshift quasar currently known, SDSS J1148+5251 (z=6.42). Our VLA data of the CO(3-2) emission have a maximum resolution of 0.''17 � 0.''13 (<=1 kpc), and enable us to resolve the molecular gas emission both ...

Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He+, C+, N+, O+, Na+, and Mg+ in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also ...

The detection in stellar spectra of underabundant molecules is investigated, with emphasis on carbon stars. The variation, as a function of the standard optical depth, of the partial pressures of various molecules including SiO, CS, HF, LiH and YH are illustrated as is the variation of the gas pressure and the temperature. Also considered are characteristic molecules in ...

Cardinal and colleagues describe the use of molecular hydrogen, the most abundant molecule in the universe, as a treatment for chronic allograft nephropathy (CAN) in a rat model of kidney transplantation. They demonstrate that the addition of hydrogen to the drinking water results in a decrease in the severity of CAN and increased graft survival, and they ...

A solution was generated for the physical properties of the Shuttle RCS 4000 N (900 lb) rocket engine exhaust plume flowfield. The modeled exhaust gas consists of the five most abundant molecular species, H2, N2, H2O, CO, and CO2. The solution is for a ba...

Abstract: This data set consists of measurements of stratospheric trace gas abundances from an ongoing experiment which is part of the Network for ...

Noble gas abundance and isotope ratios in the atmosphere of Jupiter from the Galileo Probe Mass Spectrometer. P. R. Mahaffyf H. B. Niemann,1 A. Alpert} ...

Context. This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC 1068. Unlike in other active galaxies, the intensely star-forming regions in NGC 1068 and the CND can be resolved with current instrumentation. This makes this galaxy an optimal test-bed to probe the ...

Five bright-rimmed molecular clouds, NGC 1977, IC 1396, IC 1848 A, B35, and NGC 7822, have been mapped with 30'' resolution in the J = 2--1 lines of /sup 12/co. For the first three, /sup 13/CO maps have also been made. The spatial distributions of temperature, density, and molecular abundance in these clouds have been ...

The relative efficiencies of the chemical pathways that can lead to the destruction of LiH and LiH+ molecules, conjectured to be present in the primordial gas and to control molecular cooling processes in the gravitational collapse of the post-recombination era, are revisited by using accurate quantum calculations for the several reactions involved. The ...

We have studied the dependence of the profiles of molecular abundances and line emission on the accretion flow in the hot ($\\ga 100$K) inner region of protoplanetary disks. The gas-phase reactions initiated by evaporation of the ice mantle on dust grains are calculated along the accretion flow. We focus on methanol, a molecule that is ...

Low-mass stars are formed in molecular clouds, but only in the densest and coldest regions within molecular clouds called "Dense Cores." This thesis presents a wide variety of observations, from centimeter to millimeter wavelengths observed with both single dish and interferometers, that allow us to study the star formation process in the Perseus ...

We present findings for DG Tau B and VV CrA, two of the objects observed in our Spitzer Infrared Spectrograph (IRS) project to search for molecular absorption in edge-on disks, along with near-IR spectroscopy of the CO fundamental transitions and mid-IR imaging. While the only gas absorption seen in the Spitzer IRS spectrum toward DG Tau B is CO2, we use ...

The gas phase chemistry is studied behind a 10 km s/sup -1/ shock propagating into a dense molecular cloud. Our principal conclusions are that the concentrations of certain molecules (CO, NH/sub 3/, HCN, N/sub 2/) are unperturbed by the shock; other molecules (H/sub 2/CO, CN, HCO/sup +/) are greatly decreased in abundance; and ...

Molecular beams of xenon, C$sub 4$Cl$sub 3$F$sub 7$, or C$sub 7$F$sub 14$ generated with a nozzle source using hydrogen as accelerating carrier gas are deflected by crossed free jets of ammonia. Mass spectrometric observation of the isotope abundance in the deflected xenon beam shows an increase of the intensity ratio of the ...

Electron attachment to gas phase nitrobenzene, all three isomers of mononitrotoluene and 2,4,6-trinitrotoluene is studied by means of two crossed electron-molecular beam experiments. We point out the formation of long-lived metastable parent anions and the most abundant anions produced via dissociative electron attachment (DEA). The ...

Electron attachment to gas phase nitrobenzene, all three isomers of mononitrotoluene and 2,4,6-trinitrotoluene is studied by means of two crossed electron-molecular beam experiments. We point out the formation of long-lived metastable parent anions and the most abundant anions produced via dissociative electron attachment (DEA). The ...

Aims: We aim to study the properties of the dense molecular gas towards the inner few 100 pc of four nearby starburst galaxies dominated both by photo dissociation regions (M 82) and large-scale shocks (NGC 253, IC 342, and Maffei 2), and to connect the chemical and physical properties of the molecular clouds with the evolutionary ...

A computer model for comet comae has been applied to predict ion abundances for comet Halley. It is assumed that the volatile component of the nucleus is 85% water and that the remaining volatile molecules are composed of carbon, nitrogen, oxygen, and sulfur. Model parameters such as heliocentric distance, size, and albedo are chosen to be consistent with the 13-14 March 1986 ...

The chemical composition of comet nuclei and the factors affecting it are discussed, summarizing the

The first detection of a chlorine-bearing molecular species in the interstellar medium via emission from the J = 1-0 transition of HCl at 625.9 GHz toward OMC-1 is reported. The relative strengths, widths, and velocities of the resolved hyperfine components are consistent with moderate optical depth emission originating from dense, quiescent molecular ...

Two topics are discussed here. The first is an observational study on molecular abundance in nearby (< 10 Mpc) gas-rich galaxies based on our ammonia survey and on data in literature. As a result, a systematically peculiar molecular abundance was found in a famous starburst galaxy M 82 ...

Absorption spectroscopy performed with Herschel/HIFI in the direction of bright star-forming regions of the inner Galaxy provides a new probe of the interstellar medium. The ground-state transition of several light hydrides are found to have large optical depths and are therefore sensitive tracers of gas components that are poorly known such as gas of low ...

This model written in Fortran77 can be used to compute the gas-phase chemical evolution of a dense molecular cloud at a fixed temperature and density. The model is adapted for the osu.2005 (https://www.physics.ohio-state.edu/~eric/research.html) chemical database of Eric Herbst (Ohio State University, USA) but can be modified to read any network. The model ...

Three-dimensional off-lattice Monte Carlo simulations have been used to simulate the production of interstellar dust analogues on the computer. At first, the two rather well known extreme cases of ballistic growth, i.e. particle-cluster (BPCA) and cluster-cluster aggregation (BCCA) were investigated. In a second step, we included rotation of the clusters during the growth process. Following this, ...

Measurements of absorption in the lines of (C-12)O, (C-13)O, HCO(+), HCN, CN, and CS toward the nuclear continuum source in Centaurus A are reported. The spectra show a number of features which can be attributed to individual molecular clouds with properties similar to dense molecular clouds in the Galaxy. The deepest absorption at the systemic velocity of ...

... as the molecular SiH band (387nm peak), and the molecular CH band (432nm peak). ... Independent supporting evidence of desorbed gas molecular ionization ...

The extragalactic detection of CH3CCH and CH3CN are reported, and the findings are studied to determine the excitation conditions of the dense nuclear gas component in starburst galaxies. CH3CCH, the most complex molecule observed outside the Galaxy, is detected for several mm-wave lines toward the M82SW molecular hotspot and in the nucleus of NGC253, and ...

A survey of CH 3.3 GHz emission from a sample of high-latitude molecular clouds, diffuse clouds, and heavily reddened globular clusters is presented. The F = 1-1 main-line transition was detected in every molecular cloud in the sample and in two out of four globular cluster lines of sight. The high rate of detections in the low-extinction high-latitude ...

The most usual tracer of molecular gas is line emission from CO. However, the reliability of this tracer has long been questioned in environments different from the Milky Way. We study the relationship between H2 and CO abundances using a fully dynamical model of magnetized turbulence coupled to a chemical network simplified to follow ...

A systematic investigation of dust emission associated with ionized gas has so far been performed only in our Galaxy and for wavelengths longer than 60 ?m. Newly available Spitzer data now offer the opportunity to carry out a similar analysis in the Large Magellanic Cloud (LMC). By cross-correlating Spitzer Surveying the Agents of a Galaxy's Evolution (SAGE) data with the ...

The oil-water-gas environments of oil production facilities harbour abundant and diverse microbial communities that can participate in deleterious processes such as biocorrosion. Several molecular methods, including pyrosequencing of 16S rRNA libraries, were used to characterize the microbial communities from an oil production facility ...

Context. Chemical models of dense cloud cores often utilize the so-called pseudo-time-dependent approximation, in which the physical conditions are held fixed and uniform as the chemistry occurs. In this approximation, the initial abundances chosen, which are totally atomic in nature except for molecular hydrogen, are artificial. A more detailed approach ...

Context. Bipolar outflows from Class 0 protostars often present two components in their CO spectra that have different kinematic behaviors: a smooth outflow wing and a discrete, extremely high-velocity (EHV) peak. Aims: To better understand the origin of these two outflow components, we have studied and compared their molecular composition. Methods: We carried out a ...

The 3 mm wavelength spectra of 10 galaxies have been obtained at the Five College Radio Astronomy Observatory using a new, very broadband receiver and spectrometer, called the Redshift Search Receiver (RSR). The RSR has an instantaneous bandwidth of 37 GHz covering frequencies from 74 to 111 GHz and has a spectral resolution of 31 MHz (~100 km s-1). During tests of the RSR on the FCRAO 14 m ...

We have developed a high-resolution combined physical and chemical model of a protoplanetary disk surrounding a typical T Tauri star. Our aims were to use our model to calculate the chemical structure of disks on small scales (submilliarcsecond in the inner disk for objects at the distance of Taurus, {approx}140 pc) to investigate the various chemical processes thought to be important in disks and ...

Mass and ion abundance calibration of gas chromatograph/mass spectrometer responses is essential for the production of good data. In 1975, ion abundance criteria based on the mass spectrum of decafluorotriphenylphosphine (DFTPP) were proposed to standardize quadrupole mass spectr...

Aims: We aim to investigate the chemistry and gas phase abundance of HNCO and the variation of the HNCO/CS abundance ratio as a diagnostic of the physics and chemistry in regions of massive star formation. Methods: A numerical-chemical model has been developed which self-consistently follows the chemical evolution of a hot core. The ...

We present a 190-307 GHz broadband spectrum obtained with Z-Spec of NGC 1068 with new measurements of molecular rotational transitions. After combining our measurements with those previously published and considering the specific geometry of this Seyfert 2 galaxy, we conduct a multi-species Bayesian likelihood analysis of the density, temperature, and relative ...

We investigate the formation of molecules during the chemical evolution of a cold dense interstellar cloud using a gas-grain numerical code in order to study the effects of grain-size distribution and grain growth on molecular abundances. Three initial size distributions have been used, based on earlier models. To incorporate different ...

Here we present our molecular line investigation of the southern infrared dark clouds (IRDCs). We performed observations of 13 molecular species using the 22-m Mopra radio telescope. In our survey we included in general species which are good tracers of cold and dense gas. Some of them trace the more quiescent gas ...

MOLECULAR ABUNDANCES IN COMETS JACQUES CROVISIER Observatoire de Paris, Section de Meudon, F--92195 of cometary volatiles is a basic information on the nature of comets and a clue to their formation mechanisms The molecular composition of cometary volatiles is a basic information on the nature of comets and an important

The Orion Nebula has been the subject of intensive study for over one hundred years. Far-infrared (FIR) molecular line observations of CO in the shock region surrounding the infrared source IRc2 have suggested that the molecular hydrogen density in the shocked and post-shock gas is roughly 3 x 10/sup 6/ cm/sup -3/. The temperature of ...

Sulfur is an abundant element in diffuse interstellar clouds where it remains mostly in the gas phase. However, it could deplete on dust grains at higher densities (it is still a mystery in which form sulfur can be depleted). Therefore, an accurate determination of the gas phase sulfur abundance in different ...

Upcoming facilities such as the Herschel Space Observatory or Atacama Large Millimeter Array will deliver a wealth of molecular line observations of young stellar objects (YSOs). Based on line fluxes, chemical abundances can then be estimated by radiative transfer calculations. To derive physical properties from abundances, the ...

We consider the radiative cooling of fully shielded molecular astrophysical gas over a wide range of temperatures (10K ? T ? 2500K) and H2 densities (l03 cm-3 ? n(H2) ? 1010 cm-3). Our model for the radiative cooling of molecular gas includes a detailed treatment of the interstellar chemistry that determines the ...

Molecular line observations of different galaxies allow us to study the effects of these different properties/activities on the molecular medium. In fact, some groups have suggested that it is possible to diagnose power sources in dusty galaxies using molecular line ratios. The observation of the molecular ...

We investigate the formation of molecules during the chemical evolution of a cold dense interstellar cloud using a gas-grain numerical code in order to study the effects of grain size distributions and grain growth on molecular abundances. Most models with grain surface chemistry have used so-called classical grains with a canonical ...

... instruments, Exhaust gases, Diagnostic equipment, Gas analysis, Laser induced fluorescence, Atomic spectroscopy, Molecular spectroscopy. ...

The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origin. One idea is that they result from ...

Chemical evolution of organic molecules essential to life begins in cold, pre-stellar molecular cloud cores. Given the relative lack of incident radiation, chemical reactions in these cores are dependent on interactions between their gas phase material and dust/ices. C18O and N2H+ in particular are two constituents in many pre-stellar cores that are ...

The dense cores of the M17, S140, and NGC2024 molecular clouds are studied on the basis of observations of six ortho-H2CO transitions. The observations were fitted to a grid of spherical LVG models so that the gas density and ortho-H2CO column density could be derived at many positions in each core. The resulting densities (about 1 million/cu cm) agree ...

Laboratory observations of the pure rotational spectrum of HCO(+) in its lowest excited bending state are reported. Because of their severe excitation requirements, such vibrational satellites and the high-J ground-state lines, also measured here, sample only hot, dense regions of matter in active molecular cloud cores and circumstellar envelopes. As the HCO(+) ...

Astronomical observations have shown that carbonaceous compounds in the gas and solid state, refractory and icy are ubiquitous in our and distant galaxies. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly large number of molecules that are used in contemporary ...

Molecular line observations may serve as diagnostics of the degree to which the number density of cosmic ray protons, having energies of 10s to 100s of MeV each, is enhanced in starburst galaxies and galaxies with active nuclei. Results, obtained with the UCL_PDR code, for the fractional abundances of molecules as functions of the cosmic ray induced ...

The characteristics of the plasma generated by a pulsed discharge slit nozzle (PDN) are investigated. The PDN source is designed to produce and cool molecular ions creating an astrophysically relevant environment in the laboratory. A discharge model is applied to this system to provide a qualitative as well as a quantitative picture of the plasma. We find that the ...

The primordial molecules, which appear during the phase of cosmological recombination, play an important role in the mechanisms of formation of the first gravitational structures. Their thermal influence on the gravitational dynamics of collapse can generate, under certain conditions, an instability which leads to the fragmentation of the initial collapsing structure. In this framework it is ...

We present an application of the multiphase model of Ferrini and coworkers, developed for the solar neighborhood, to other regions of the disk of the Galaxy in order to reproduce the observed element abundance gradients. The model describes the Galaxy as a two-zone system (halo and disk) sliced into nine cylindrical concentric regions and studies the time evolution of the five ...

We present interstellar gas-phase abundances of zinc and chromium in the Milky Way for comparison with the abundances of these elements in damped Ly-alpha systems at redshifts near z approximately 2. We make use of both IUE (International Ultraviolet Explorer) and GHRS (Goddard High Resolution Spectrograph) archival information in ...

... Descriptors : *MOLECULAR SPECTROSCOPY, *ATOMIC SPECTROSCOPY, *EXHAUST GASES ... LASER INDUCED FLUORESCENCE, PLASMAS ...

... DETECTORS, FLUORESCENCE, TUNABLE ... MOLECULAR SPECTROSCOPY, EXCITATION ... MANAGEMENT, ATOMIC SPECTROSCOPY, INDIUM ...

Definition: Oxygen (O) (and molecular oxygen (O2)) is the second most abundant species in the atmosphere. The abundance of O2 remains fairly constant in the ...

A detailed non-LTE analysis of solar CN spectra strongly suggest a revised carbon abundance for the

We present Very Large Array observations of NH3 (1,1) and (2,2) in a sample of six infrared-dark clouds (IRDCs) with distances from 2 to 5 kpc. We find that ammonia serves as an excellent tracer of dense gas in IRDCs, showing no evidence of depletion, and the average abundance in these clouds is 8.1 � 10�7. Our sample consists of four IRDCs with 24 ?m ...

We present new observations of the D2CO emission towards the small cloud L1689N in the rho Ophiuchus complex. We surveyed five positions, three being a cut across a shock site and two probing the quiescent gas of the molecular cloud. We detected D2CO emission in the first three positions. The measured [D2CO]/[H2CO] is about 3%, whereas it is <=2% in the ...

A large gas-phase chemical model of interstellar molecular clouds containing almost 4,000 gas-phase reactions involving 409 species are developed. The calculated results are in excellent agreement with observed abundances in TMC1. The effects of rapid neutral-neutral reactions in the gas phase ...

Context. The identification of the carriers of the diffuse interstellar bands (DIBs) is the longest standing problem in the study of the interstellar medium. Here we present recent UV laboratory spectra of various polycyclic aromatic hydrocarbons (PAHs) and explore the potential of these molecules as carriers of the DIBs. Whereas, in the near IR range, the PAHs exhibit vibrational bands that are ...

Research in the use of FIR and sub-mm lines to provide data relevant to astrochemistry is examined. Spectroscopic features in the FIR and sub-mm are dominated by transitions from species of atoms and atomic ions, metal hydrides, and heavy molecules. The data of Lester et al.(1983) and Dinerstein et al. (1984) on the N/O abundance ratio are discussed. The N/O ...

Laboratory and observational studies of the formation and presence of u2saturated long carbon chain molecules of the form HC(2n+1)N, which have been observed in interstellar space, are discussed. Experiments with cyanopolyyne formation under radio frequency discharges in mixtures of acetylene and hydrogen cyanide have suggested that the long chain carbon molecules are formed by addition onto the ...

Hydrocarbon analysis with standard GC-MS is confronted by the limited range of volatile compounds amenable for analysis and by the similarity of electron ionization mass spectra for many compounds which show weak or no molecular ions for heavy hydrocarbons. The use of GC-MS with supersonic molecular beams (Supersonic GC-MS) significantly extends the range ...