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 The gas-phase chemistry of carbon chains in dark cloud chemical models

2013 ◽  
Vol 437 (1) ◽  
pp. 930-945 ◽  
Author(s):  
Jean-Christophe Loison ◽  
Valentine Wakelam ◽  
Kevin M. Hickson ◽  
Astrid Bergeat ◽  
Raphael Mereau
Keyword(s):  
Gas Phase ◽  
Dark Cloud ◽  
Gas Phase Chemistry ◽  
Chemical Models ◽  
Carbon Chains ◽  
Phase Chemistry

scholarly journals Review of OCS gas-phase reactions in dark cloud chemical models

2012 ◽  
Vol 421 (2) ◽  
pp. 1476-1484 ◽  
Author(s):  
Jean-Christophe Loison ◽  
Philippe Halvick ◽  
Astrid Bergeat ◽  
Kevin M. Hickson ◽  
Valentine Wakelam
Keyword(s):  
Gas Phase ◽  
Gas Phase Reactions ◽  
Dark Cloud ◽  
Chemical Models

scholarly journals A Revised Description of the Cosmic Ray Induced Desorption of Interstellar Ices

2021 ◽  
Vol 922 (2) ◽  
pp. 126
Author(s):  
Olli Sipilä ◽  
Kedron Silsbee ◽  
Paola Caselli
Keyword(s):  
Gas Phase ◽  
Cosmic Ray ◽  
Equilibrium Temperature ◽  
Cooling Time ◽  
Transient Heating ◽  
Two Phase ◽  
Chemical Models ◽  
Three Phase ◽  
Prestellar Cores ◽  
Phase Chemical

Abstract Nonthermal desorption of ices on interstellar grains is required to explain observations of molecules that are not synthesized efficiently in the gas phase in cold dense clouds. Perhaps the most important nonthermal desorption mechanism is one induced by cosmic rays (CRs), which, when passing through a grain, heat it transiently to a high temperature—the grain cools back to its original equilibrium temperature via the (partial) sublimation of the ice. Current cosmic ray induced desorption (CRD) models assume a fixed grain cooling time. In this work, we present a revised description of CRD in which the desorption efficiency depends dynamically on the ice content. We apply the revised desorption scheme to two-phase and three-phase chemical models in physical conditions corresponding to starless and prestellar cores, and to molecular cloud envelopes. We find that, inside starless and prestellar cores, introducing dynamic CRD can decrease gas-phase abundances by up to an order of magnitude in two-phase chemical models. In three-phase chemical models, our model produces results very similar to those of the static cooling scheme—when only one monolayer of ice is considered active. Ice abundances are generally insensitive to variations in the grain cooling time. Further improved CRD models need to take into account additional effects in the transient heating of the grains—introduced, for example, by the adoption of a spectrum of CR energies.

scholarly journals Discovery of CH2CHCCH and detection of HCCN, HC4N, CH3CH2CN, and, tentatively, CH3CH2CCH in TMC-1

2021 ◽  
Vol 647 ◽  
pp. L2 ◽  
Author(s):  
J. Cernicharo ◽  
M. Agúndez ◽  
C. Cabezas ◽  
N. Marcelino ◽  
B. Tercero ◽  
...  
Keyword(s):  
Gas Phase ◽  
Column Density ◽  
State Of The Art ◽  
Closed Shell ◽  
Abundance Ratio ◽  
Chemical Model ◽  
Dark Cloud ◽  
First Time ◽  
Phase Chemical

We present the discovery in TMC-1 of vinyl acetylene, CH2CHCCH, and the detection, for the first time in a cold dark cloud, of HCCN, HC4N, and CH3CH2CN. A tentative detection of CH3CH2CCH is also reported. The column density of vinyl acetylene is (1.2 ± 0.2) × 1013 cm−2, which makes it one of the most abundant closed-shell hydrocarbons detected in TMC-1. Its abundance is only three times lower than that of propylene, CH3CHCH2. The column densities derived for HCCN and HC4N are (4.4 ± 04) × 1011 cm−2 and (3.7 ± 0.4) × 1011 cm−2, respectively. Hence, the HCCN/HC4N abundance ratio is 1.2 ± 0.3. For ethyl cyanide we derive a column density of (1.1 ± 0.3) × 1011 cm−2. These results are compared with a state-of-the-art chemical model of TMC-1, which is able to account for the observed abundances of these molecules through gas-phase chemical routes.

Polarimetric and photometric observations of CB54, with analysis of four other dark clouds

2021 ◽  
Vol 503 (4) ◽  
pp. 5274-5290
Author(s):  
A K Sen ◽  
V B Il’in ◽  
M S Prokopjeva ◽  
R Gupta
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Galactic Plane ◽  
Photometric Data ◽  
Dust Particles ◽  
Dark Cloud ◽  
Dark Clouds ◽  
High Polarization ◽  
Field Parallel ◽  
Photometric Observations

ABSTRACT We present the results of our BVR-band photometric and R-band polarimetric observations of ∼40 stars in the periphery of the dark cloud CB54. From different photometric data, we estimate E(B − V) and E(J − H). After involving data from other sources, we discuss the extinction variations towards CB54. We reveal two main dust layers: a foreground, E(B − V) ≈ 0.1 mag, at ∼200 pc and an extended layer, $E(B-V) \gtrsim 0.3$ mag, at ∼1.5 kpc. CB54 belongs to the latter. Based on these results, we consider the reason for the random polarization map that we have observed for CB54. We find that the foreground is characterized by low polarization ($P \lesssim 0.5$ per cent) and a magnetic field parallel to the Galactic plane. The extended layer shows high polarization (P up to 5–7 per cent). We suggest that the field in this layer is nearly perpendicular to the Galactic plane and both layers are essentially inhomogeneous. This allows us to explain the randomness of polarization vectors around CB54 generally. The data – primarily observed by us in this work for CB54, by A. K. Sen and colleagues in previous works for three dark clouds CB3, CB25 and CB39, and by other authors for a region including the B1 cloud – are analysed to explore any correlation between polarization, the near-infrared, E(J − H), and optical, E(B − V), excesses, and the distance to the background stars. If polarization and extinction are caused by the same set of dust particles, we should expect good correlations. However, we find that, for all the clouds, the correlations are not strong.

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.

Synthesis of polymorphic titanium oxide nanoparticles by a rapid gas-phase chemical reaction

2016 ◽  
Vol 26 (2) ◽  
pp. 157-159 ◽  
Author(s):  
Ning Luo ◽  
Hong Wen Jing ◽  
Zhan Guo Ma ◽  
Weidong Liu ◽  
Liangchi Zhang ◽  
...  
Keyword(s):  
Gas Phase ◽  
Titanium Oxide ◽  
Chemical Reaction ◽  
Oxide Nanoparticles ◽  
Titanium Oxide Nanoparticles ◽  
Phase Chemical
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