scholarly journals Non thermal sputtering of grains and production of SiO in interstellar shocks

1997 ◽  
Vol 178 ◽  
pp. 113-128 ◽  
Author(s):  
Guillaume Pineau Des Forêts ◽  
David Flower
Keyword(s):  
Gas Phase ◽  
Satisfactory Agreement ◽  
Shock Model ◽  
Dense Gas ◽  
Heavy Particles ◽  
Molecular Outflows ◽  
Dark Clouds ◽  
Interstellar Grains ◽  
Upper Limits ◽  
Interstellar Shocks

We present recent results for the yields of Si and O, produced in the sputtering of SiO2 by ions of different masses, and show the importance of sputtering by heavy particles at low streaming velocities. These data are incorporated in a C-shock model to study the erosion of interstellar grains and the release of silicon through non-thermal sputtering within the shock. Once in the gas phase, the atomic silicon reacts with O2 and is rapidly transformed into SiO. The column densities of SiO thus calculated are compared with the observations of molecular outflows with a satisfactory agreement. In the postshock gas, SiO disappears from the gas phase through the reaction SiO(OH,H)SiO2 and SiO2 remains, unseen, in the cold dense gas. This could explain the extremely low upper limits of SiO deduced from observations of dark clouds.

scholarly journals Interaction between molecular outflows and dense gas in the cluster-forming region OMC-2/FIR4

2006 ◽  
Vol 2 (S237) ◽  
pp. 475-475
Author(s):  
Yoshito Shimajiri ◽  
S. Takahashi ◽  
S. Takakuwa ◽  
M. Saito ◽  
R. Kawabe
Keyword(s):  
Cluster Formation ◽  
Major Axis ◽  
List Type ◽  
Dense Gas ◽  
Continuum Source ◽  
Molecular Outflows ◽  
Molecular Outflow ◽  
Dense Cores ◽  
Potential Source ◽  
Molecular Lines

AbstractSince most stars are born as members of clusters (Lada & Lada 2003), it is important to clarified the detailed mechanism of cluster formation for comprehensive understanding of star formation. However, our current understanding of cluster formation is limited due to the followings; (a)Cluster forming regions are located at the far distance.(b)There are complex mixtures of outflows and dense gas in cluster forming regions. So, we focused on the Orion Molecular Cloud 2 region (OMC-2), a famous cluster-forming region (Lada & Lada 2003) and the most nearest GMC. We observed the FIR 4 region with the Nobeyama Millimeter Array(NMA), Atacama Submillimeter Telescope Experiment (ASTE). In this region, there are 3 protostars (FIR3, FIR4, FIR5) which were identified as 1.3 mm dust continuum sources (Chini et al. 1997) and driving sources of mixed outflows, and FIR 4 is the most strongest source of 1.3 mm dust continuum in OMC-2. Molecular lines we adopted are a high density (105cm−3) gas tracer of H13CO+ (J=1-0), a molecular outflow tracer of 12CO(J=1-0) and 12CO(J=3-2), and SiO(J=2-1 v=0) as a tracer of shocks associated with an interaction between outflows and dense gas.From results of the 12CO(J=1-0) outflow, H13CO+ dense gas, and the SiO shock, the outflow from FIR 3 interacts with dense gas in the FIR 4 region. Moreover the Position-Velocity diagram along the major axis of the 12CO(J=3-2) outflow shows that the 12CO(J=1-0) and SiO emission exhibits a L shape (the line widths increase in the interacting region in morphology). This is an evidence of interaction between the outflows and dense gas (Takakuwa et al. 2003). From result of the 3 mm dust continuum, the interacted region by the molecular outflow of FIR 3 is an assemble of seven dense cores. The mass of each core is 0.1-0.8 M. This clumpy structure is evident only at FIR 4 in the entire OMC-2/3 region. There are possible that two cores are in the proto-stellar phase, because 3 mm dust continuum source correspond to NIR source or 3.6 cm f-f jet source. From these results, cores in the FIR 4 region may be potential source of the next-generation stars. In the other words, there is a possibility that the molecular outflow ejected from FIR 3 is triggering the cluster formation in the FIR 4 region.

scholarly journals The role of radiolysis in the modelling of C2H4O2 isomers and dimethyl ether in cold dark clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 3414-3424
Author(s):  
Alec Paulive ◽  
Christopher N Shingledecker ◽  
Eric Herbst
Keyword(s):  
Gas Phase ◽  
Dimethyl Ether ◽  
Recent Observation ◽  
Cosmic Ray ◽  
Thermal Method ◽  
Dark Clouds ◽  
Ice Surface ◽  
Dust Grain ◽  
Complex Organic

ABSTRACT Complex organic molecules (COMs) have been detected in a variety of interstellar sources. The abundances of these COMs in warming sources can be explained by syntheses linked to increasing temperatures and densities, allowing quasi-thermal chemical reactions to occur rapidly enough to produce observable amounts of COMs, both in the gas phase, and upon dust grain ice mantles. The COMs produced on grains then become gaseous as the temperature increases sufficiently to allow their thermal desorption. The recent observation of gaseous COMs in cold sources has not been fully explained by these gas-phase and dust grain production routes. Radiolysis chemistry is a possible non-thermal method of producing COMs in cold dark clouds. This new method greatly increases the modelled abundance of selected COMs upon the ice surface and within the ice mantle due to excitation and ionization events from cosmic ray bombardment. We examine the effect of radiolysis on three C2H4O2 isomers – methyl formate (HCOOCH3), glycolaldehyde (HCOCH2OH), and acetic acid (CH3COOH) – and a chemically similar molecule, dimethyl ether (CH3OCH3), in cold dark clouds. We then compare our modelled gaseous abundances with observed abundances in TMC-1, L1689B, and B1-b.

scholarly journals Reactive quenching of electronically excited NO<sub>2</sub><sup>∗</sup> and NO<sub>3</sub><sup>∗</sup> by H<sub>2</sub>O as potential sources of atmospheric HO<sub><i>x</i></sub> radicals

2018 ◽  
Vol 18 (19) ◽  
pp. 14005-14015 ◽  
Author(s):  
Terry J. Dillon ◽  
John N. Crowley
Keyword(s):  
Gas Phase ◽  
Laser Excitation ◽  
Pulsed Laser ◽  
Work Rate ◽  
Rate Coefficients ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Upper Limit ◽  
Upper Limits ◽  
Electronically Excited

Abstract. Pulsed laser excitation of NO2 (532–647 nm) or NO3 (623–662 nm) in the presence of H2O was used to initiate the gas-phase reaction NO2∗+H2O → products (Reaction R5) and NO3∗+H2O → products (Reaction R12). No evidence for OH production in Reactions (R5) or (R12) was observed and upper limits for OH production of k5b/k5<1×10-5 and k12b/k12<0.03 were assigned. The upper limit for k5b∕k5 renders this reaction insignificant as a source of OH in the atmosphere and extends the studies (Crowley and Carl, 1997; Carr et al., 2009; Amedro et al., 2011) which demonstrate that the previously reported large OH yield by Li et al. (2008) was erroneous. The upper limit obtained for k12b∕k12 indicates that non-reactive energy transfer is the dominant mechanism for Reaction (R12), though generation of small but significant amounts of atmospheric HOx and HONO cannot be ruled out. In the course of this work, rate coefficients for overall removal of NO3∗ by N2 (Reaction R10) and by H2O (Reaction R12) were determined: k10=(2.1±0.1)×10-11 cm3 molecule−1 s−1 and k12=(1.6±0.3)×10-10 cm3 molecule−1 s−1. Our value of k12 is more than a factor of 4 smaller than the single previously reported value.

scholarly journals The Gas-phase Chemical Evolution of Dark Clouds

1992 ◽  
Vol 45 (4) ◽  
pp. 451
Author(s):  
RPA Bettens
Keyword(s):  
Gas Phase ◽  
Chemical Species ◽  
Dynamical Evolution ◽  
Constant Density ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Chemical Models ◽  
Almost All ◽  
Present Understanding ◽  
Phase Chemical

A rich chemistry exists within dark clouds. In the most chemically studied dark cloud, Taurus molecular cloud one (TMC-l), more than 40 molecules have been detected. In this paper I look at the current isochoric, i.e. constant density, isothermal time-dependent gas-phase chemical models of dark clouds such as TMC-l and very briefly outline the present understanding of the chemistry of these objects. The above chemical models agree very well with the observed abundances of almost all chemical species at times earlier than steady state, i.e. earlier than thirty million years. However, the models are fraught with uncertainty and are not physically realistic representations of the full dynamical evolution of dark clouds from a more diffuse state. Nevertheless the agreement with observation is striking.

scholarly journals Molecules in nearby and primordial supernovae

2008 ◽  
Vol 4 (S251) ◽  
pp. 221-226
Author(s):  
Isabelle Cherchneff ◽  
Simon Lilly
Keyword(s):  
Gas Phase ◽  
Early Universe ◽  
Organic Molecules ◽  
Molecular Form ◽  
Chemical Kinetic ◽  
Kinetic Approach ◽  
Dust Formation ◽  
Core Collapse ◽  
Chemical Models ◽  
Upper Limits

AbstractWe present new chemical models of supernova (SN) ejecta based on a chemical kinetic approach. We focus on the formation of inorganic and organic molecules including gas phase dust precursors, and consider zero-metallicity progenitor, massive supernovae and nearby core-collapse supernovae such as SN1987A. We find that both types are forming large amounts of molecules in their ejecta at times as early as 200 days after explosion. Upper limits on the dust formation budget are derived. Our results on dust precursors do not agree with existing studies on dust condensation in SN ejecta. We conclude that PMSNe could be the first non-primodial molecule providers in the early universe, ejecting up to 34% of their progenitor mass under molecular form to the pristine, local gas.

scholarly journals A large scale survey of dense cores and molecular outflows in Ophiuchus

1991 ◽  
Vol 147 ◽  
pp. 462-463
Author(s):  
Akira Mizuno ◽  
Satonori Nozawa ◽  
Takahiro Iwata ◽  
Yasuo Fukui
Keyword(s):  
High Velocity ◽  
Large Scale ◽  
Mass Density ◽  
Point Sources ◽  
Main Body ◽  
Grid Spacing ◽  
Molecular Outflows ◽  
Dark Clouds ◽  
Dense Cores ◽  
Large Scale Survey

We have been surveying dense molecular cores in Ophiuchus region including ρ Oph, L234, and L43 with the 4m radio telescope at Nagoya University since 1985. We have already mapped ∼18° × 12° area with 2′ or 4′ grid spacing in 13CO (J=1-0) spectra. We have identified ∼50 dense cores (we call ”13CO cores”). Typical mass, density, and size of the 13CO cores are ∼20 M⊙, ∼3 × 103 cm−3, and ∼0.3 pc, respectively (Nozawa et al. 1990). We also surveyed molecular outflows in 12CO (J=1-0) spectra toward 13 IRAS point sources associated with 13CO cores in Ophiuchus. As a result of the survey, we have found 5 molecular outflows in the filamentary dark clouds and 5 regions exhibiting high velocity wings in the ρ Oph main body.

scholarly journals Effects of reducing the reactor diameter on the dense gas–solid fluidization of very heavy particles: 3D numerical simulations

2017 ◽  
Vol 117 ◽  
pp. 575-583 ◽  
Author(s):  
Renaud Ansart ◽  
Florence Vanni ◽  
Brigitte Caussat ◽  
Carine Ablitzer ◽  
Méryl Brothier
Keyword(s):  
Numerical Simulations ◽  
Dense Gas ◽  
Heavy Particles ◽  
Reactor Diameter

A search for a gas-phase free-radical inversion displacement reaction at a saturated carbon atom

1983 ◽  
Vol 61 (5) ◽  
pp. 916-920 ◽  
Author(s):  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Side Reactions ◽  
Forward Reaction ◽  
Reaction Systems ◽  
Upper Limit ◽  
Upper Limits ◽  
Decomposition Of Methane ◽  
Simple Inversion ◽  
Saturated Carbon Atom

Five thermal and photochemical reaction systems have been examined in an attempt to detect or to place upper limits on the rates of the simple inversion reaction, CH3 + CH4 → C2H6 + H, and its reverse. No positive evidence was obtained for the occurrence of these reactions. An upper limit for the rate constant for the forward reaction of 0.063 M−1s−1 at 802 K was obtained from the thermal decomposition of methane, and upper limits of 0.044 and 0.14 at 823 and 983 K respectively were estimated from the thermal decomposition of ethane. Other systems examined were the thermal decomposition of azomethane in the presence of methane, and the mercury-photosensitized decompositions of methane and ethane, which were complicated by unexpected side reactions.

Electron attachment to amides studied by low-pressure chemical ionization and electron swarms: comparison of the gas and liquid phase

1985 ◽  
Vol 63 (5) ◽  
pp. 560-566 ◽  
Author(s):  
T. H. Tran-Thi ◽  
A. M. Koulkès-Pujo
Keyword(s):  
Liquid Phase ◽  
Gas Phase ◽  
Chemical Ionization ◽  
Electron Attachment ◽  
Low Pressure ◽  
Density Effect ◽  
Dense Gas ◽  
Liquid Phases ◽  
Pressure Chemical Ionization ◽  
Pressure Chemical

The low-pressure chemical ionization and electron swarm techniques were used to determine the density effect of the environment in the case of electron attachment to four linear or cyclic, primary or substituted amides: N-methylacetamide, dimethylacetamide, pyrrolidone, and N-methylpyrrolidone. The results are compared with those obtained previously for the same compounds in polar liquid phases, where they have been used either as solutes or as solvating media. From this comparison, the electron attachment scheme proposed for the dense gas phase was extended to the liquid phase.

scholarly journals Deuterium Fractionation and Ionization Degree in Massive Protostellar/cluster Cores

2012 ◽  
Vol 8 (S292) ◽  
pp. 40-40
Author(s):  
Huei-Ru Chen ◽  
Sheng-Yuan Liu ◽  
Yu-Nung Su
Keyword(s):  
High Mass ◽  
Evolutionary Stage ◽  
Gas Temperature ◽  
Ionization Degree ◽  
Dark Clouds ◽  
Dense Cores ◽  
General Chemical ◽  
Upper Limits ◽  
Cluster Cores ◽  
Infrared Extinction

AbstractWe have conducted a survey of deuterium fractionation of N2H+, RD(N2H+) ≡ N(N2D+)/N(N2H+), with the Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) to assess the use of RD(N2H+) as an evolutionary tracer among massive protostellar/cluster cores in early stages. Our sample includes 32 dense cores in various evolutionary stages, from high-mass starless cores (HMSCs), high-mass protostellar objects (HMPOs), to ultra-compact (UC) HII regions, in infrared dark clouds (IRDCs) and high infrared extinction clouds. The results show a decreasing trend in deuterium fractionation with evolutionary stage traced by gas temperature and line width (Fig. 1). A moderate increasing trend of deuterium fractionation with the CO depletion factor is also found among cores in IRDCs and HMSCs. These suggest a general chemical behavior of deuterated species in low- and high-mass protostellar candidates. Upper limits to the ionization degree are also estimated to be in the range of 4 × 10−8 − 5 × 10−6.

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