scholarly journals The Sensitivity of Gas‐Phase Chemical Models of Interstellar Clouds to C and O Elemental Abundances and to a New Formation Mechanism for Ammonia

1998 ◽  
Vol 501 (1) ◽  
pp. 207-220 ◽  
Author(s):  
R. Terzieva ◽  
Eric Herbst
Keyword(s):  
Gas Phase ◽  
Formation Mechanism ◽  
Interstellar Clouds ◽  
Elemental Abundances ◽  
Chemical Models ◽  
New Formation ◽  
Phase Chemical

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 Evolutionary Models of Interstellar Chemistry

1992 ◽  
Vol 150 ◽  
pp. 205-210
Author(s):  
Sheo S. Prasad
Keyword(s):  
Gas Phase ◽  
Chemical Processes ◽  
Evolutionary Models ◽  
Evolutionary Perspective ◽  
Interstellar Chemistry ◽  
Interstellar Clouds ◽  
Dynamical Equilibrium ◽  
Chemical Models ◽  
Gas Phase Molecules ◽  
Fixed Condition

Evolutionary chemical models are ultimately unavoidable for a full understanding of interstellar clouds. They include not only the chemical processes but also the dynamical processes by which the modeled object came to be the way it is. From an evolutionary perspective, dark cores may be ephemeral objects and dynamical equilibrium an exception rather than norm. Evolutionary models have numerous advantages over “classical” fixed condition equilibrium models. They have the potential to provide more elegant explanations for the observed inter-cloud and intra-cloud chemical differences. The problem of the depletion of gas phase molecules by condensation onto the grain may also be less serious in evolutionary models. Hence, these models should be actively developed.

Observation of covalent and electrostatic bonds in nitrogen-containing polycyclic ions formed by gas phase reactions of the benzene radical cation with pyrimidine

2017 ◽  
Vol 19 (9) ◽  
pp. 6422-6432 ◽  
Author(s):  
Isaac Kwame Attah ◽  
Abdel-Rahman Soliman ◽  
Sean P. Platt ◽  
Michael Meot-Ner (Mautner) ◽  
Saaudallah G. Aziz ◽  
...  
Keyword(s):  
Gas Phase ◽  
Radical Cation ◽  
Formation Mechanism ◽  
Gas Phase Reactions ◽  
New Formation

This work reports a new formation mechanism for the nitrogen-containing polycyclic ions in the gas phase.

scholarly journals Evolution of the abundance of biomolecules in the interstellar medium at the gas phase

2009 ◽  
Vol 5 (S265) ◽  
pp. 438-439
Author(s):  
Eduardo M. Penteado ◽  
Helio J. Rocha-Pinto
Keyword(s):  
Gas Phase ◽  
Chemical Evolution ◽  
Chemical Compositions ◽  
Small Bodies ◽  
Interstellar Clouds ◽  
Elemental Abundances ◽  
Habitable Zones ◽  
Consistent Model ◽  
The Galaxy ◽  
Rocky Planets

AbstractInterstellar clouds are the sites where many molecules believed important for the early life are produced. The collapse of such clouds may give birth to stars hosting planetary systems. During the formation of such systems, molecules formed in the molecular cloud, aggregated into grains, can be incorporated in protoplanets, influencing the chemical evolution of the environment, probably affecting the chances for appearance of life on rocky planets located at the stellar habitable zones. Moreover, small bodies, like comets, can carry some of these molecules to inner planets of their systems. Using astrochemical equations, we describe the evolution of the abundance of such molecules at the gas phase from several initial interstellar compositions. These varying initial chemical compositions consider the change of the elemental abundances predicted by a self-consistent model of the chemical evolution of the Galaxy. A system of first order differential equations that describes the abundances of each molecule is solved numerically. This poster describes an innovative attempt to link the astrochemistry equations with the Galactic chemical evolution.

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.

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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