scholarly journals FastChem: A computer program for efficient complex chemical equilibrium calculations in the neutral/ionized gas phase with applications to stellar and planetary atmospheres

2018 ◽  
Author(s):  
Joachim W Stock ◽  
Daniel Kitzmann ◽  
A Beate C Patzer ◽  
Erwin Sedlmayr
Keyword(s):  
Computer Program ◽  
Gas Phase ◽  
Chemical Equilibrium ◽  
Planetary Atmospheres ◽  
Ionized Gas ◽  
Complex Chemical ◽  
Equilibrium Calculations

scholarly journals Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

2020 ◽  
Vol 637 ◽  
pp. A59 ◽  
Author(s):  
M. Agúndez ◽  
J. I. Martínez ◽  
P. L. de Andres ◽  
J. Cernicharo ◽  
J. A. Martín-Gago
Keyword(s):  
Gas Phase ◽  
Chemical Equilibrium ◽  
Equilibrium Composition ◽  
Building Blocks ◽  
Carbon Clusters ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
General Chemical ◽  
First Time ◽  
Equilibrium Calculations

Chemical equilibrium has proven extremely useful for predicting the chemical composition of AGB atmospheres. Here we use a recently developed code and an updated thermochemical database that includes gaseous and condensed species involving 34 elements to compute the chemical equilibrium composition of AGB atmospheres of M-, S-, and C-type stars. We include for the first time TixCy clusters, with x = 1–4 and y = 1–4, and selected larger clusters ranging up to Ti13C22, for which thermochemical data are obtained from quantum-chemical calculations. Our main aims are to systematically survey the main reservoirs of each element in AGB atmospheres, review the successes and failures of chemical equilibrium by comparing it with the latest observational data, identify potentially detectable molecules that have not yet been observed, and diagnose the most likely gas-phase precursors of dust and determine which clusters might act as building blocks of dust grains. We find that in general, chemical equilibrium reproduces the observed abundances of parent molecules in circumstellar envelopes of AGB stars well. There are, however, severe discrepancies of several orders of magnitude for some parent molecules that are observed to be anomalously overabundant with respect to the predictions of chemical equilibrium. These are HCN, CS, NH3, and SO2 in M-type stars, H2O and NH3 in S-type stars, and the hydrides H2O, NH3, SiH4, and PH3 in C-type stars. Several molecules have not yet been observed in AGB atmospheres but are predicted with non-negligible abundances and are good candidates for detection with observatories such as ALMA. The most interesting ones are SiC5, SiNH, SiCl, PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO, ZrO, VO, FeS, CoH, and NiS. In agreement with previous studies, the first condensates predicted to appear in C-rich atmospheres are found to be carbon, TiC, and SiC, while Al2O3 is the first major condensate expected in O-rich outflows. According to our chemical equilibrium calculations, the gas-phase precursors of carbon dust are probably acetylene, atomic carbon, and/or C3, while for silicon carbide dust, the most likely precursors are the molecules SiC2 and Si2C. In the case of titanium carbide dust, atomic Ti is the major reservoir of this element in the inner regions of AGB atmospheres, and therefore it is probably the main supplier of titanium during the formation of TiC dust. However, chemical equilibrium predicts that large titanium-carbon clusters such as Ti8C12 and Ti13C22 become the major reservoirs of titanium at the expense of atomic Ti in the region where condensation of TiC is expected to occur. This suggests that the assembly of large TixCy clusters might be related to the formation of the first condensation nuclei of TiC. In the case of Al2O3 dust, chemical equilibrium indicates that atomic Al and the carriers of Al-O bonds AlOH, AlO, and Al2O are the most likely gas-phase precursors.

Theoretical and experimental study of chemical equilibrium in the systems Si-Cl and Si-Cl-H. Calculation of chemical equilibrium in the systems Si-Cl and Si-Cl-H

1989 ◽  
Vol 54 (11) ◽  
pp. 2896-2909 ◽  
Author(s):  
Jindřich Leitner ◽  
Čestmír Černý ◽  
Petr Voňka ◽  
Jan Mikulec
Keyword(s):  
Gas Phase ◽  
Chemical Equilibrium ◽  
Atmospheric Pressure ◽  
Total Pressure ◽  
Equilibrium Composition ◽  
Molar Ratio ◽  
Initial Composition ◽  
Chemical Equilibria ◽  
First Time ◽  
Equilibrium Calculations

From the calculations of heterogenous chemical equilibria in the systems Si-Cl and Si-Cl-H the equilibrium composition of the gas phase and the amount of deposited or reacted solid silicon have been determined. For these calculations, the method based on the minimization of the Gibbs energy of the system and critically judged and selected values of input thermodynamic data have been used. The calculations have been performed for the temperature range 1 000-1 600 K, for the pressure 101.325 kPa and 10.133 kPa and for various input compositions of the gaseous phase. In the case of the system Si-Cl, the reaction of solid leading to the formation of silicon subchlorides takes place at all conditions investigated. At atmospheric pressure and at temperatures in the neighbourhood of 1 300 K, the dominant components of the gas phase are the following substances: SiCl4, SiCl3 and SiCl2. The dependence of the amount of deposited solid silicon on temperature and on the initial composition of the gas phase in the system Si-Cl-H shows–in the investigated range of variables – a maximum, the position of which depends on the total pressure of the system. At atmospheric pressure, at temperatures around 1 300 K and at the initial molar ratio Cl/H = 0.01, the dominant components of the gas phase are the following substances: SiCl4, SiCl3, SiCl2, SiHCl3, SiH2Cl2 and HCl. The substance SiHCl which has been included into the equilibrium calculations for the first time, is present in a significant amount at higher temperatures and especially at lower pressure.

Theoretical Study of Gas-Phase Thermodynamics Relevant to Silicon Carbide Chemical Vapor Deiposition

1991 ◽  
Vol 250 ◽  
Author(s):  
Mark D. Allendorf ◽  
Carl F. Melius
Keyword(s):  
Silicon Carbide ◽  
Gas Phase ◽  
Theoretical Study ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Equilibrium Calculations

AbstractEquilibrium calculations are reported for conditions typical of silicon carbide (SiC) deposition from mixtures of silane and hydrocarbons. Included are 34 molecules containing both silicon and carbon, allowing an assessment to be made of the importance of organosilicon species (and organosilicon radicals in particular) to the deposition process. The results are used to suggest strategies for improved operation of SiC CVD processes.

scholarly journals Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

2007 ◽  
Vol 7 (3) ◽  
pp. 9203-9233 ◽  
Author(s):  
C. Fountoukis ◽  
A. Nenes ◽  
A. Sullivan ◽  
R. Weber ◽  
T. VanReken ◽  
...  
Keyword(s):  
Gas Phase ◽  
Mexico City ◽  
Thermodynamic Equilibrium ◽  
Phase State ◽  
Molar Ratio ◽  
Inorganic Species ◽  
Equilibrium Calculations ◽  
Thermodynamic Equilibrium Model ◽  
Thermodynamic Equilibrium Calculations

Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. Semi-volatile partitioning equilibrates on a timescale between 6 and 20 min. When the aerosol sulfate-to-nitrate molar ratio is less than 1, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatically. This suggests that explicitly considering crustals in the thermodynamic calculations are required to accurately predict the partitioning and phase state of aerosols.

Electronic Spectra of the Triacetylene Cation (HC6H+) and Protonated Triacetylene (HC6H2+) Tagged with Ar

2019 ◽  
Vol 72 (4) ◽  
pp. 260 ◽  
Author(s):  
Ugo Jacovella ◽  
Giel Muller ◽  
Katherine J. Catani ◽  
Nastasia I. Bartlett ◽  
Evan J. Bieske
Keyword(s):  
Electronic Spectrum ◽  
Gas Phase ◽  
Band System ◽  
Argon Atom ◽  
Planetary Atmospheres ◽  
Phase Spectrum ◽  
Tandem Mass ◽  
Interstellar Clouds ◽  
Combustion Processes ◽  
First Time

Polyacetylene cations (HC2nH+) play important roles in combustion processes and in the chemistry of planetary atmospheres and interstellar clouds. Here we report the electronic spectrum for the triacetylene cation (HC6H+) recorded over the 300–610nm range by photodissociating mass-selected ions tagged with argon atoms in a tandem mass spectrometer. The spectrum shows three band systems that are assigned to (origin transition 16665cm−1), (origin transition 23916cm−1), and (origin transition 29920cm−1). Although the band system is well known, the and band systems are observed for the first time in the gas phase. In addition, the electronic spectrum of the protonated triacteylene cation tagged with an argon atom (HC6-Ar) is reported, providing the first gas-phase spectrum for this species.

Sign in / Sign up

Export Citation Format

Share Document