Reaction Mechanism Formats

Reaction data, thermodynamic properties, and transport properties are imported in the standard format.

All species in gas phase and/or surface data files must have unique names.
Lines in an input file that start with an exclamation mark (!) are regarded as comments.

Gas Chemistry Reaction Files

The gas phase data files state the chemical elements and species that are included in the mechanism. The elements and species are followed by a list of possible reactions that the species can participate in, and the corresponding variables, $A$ , $n$ ( $β$ in Eqn. (3365)), and $E_{a}$ , that are used by the Arrhenius law Eqn. (3365) to calculate the rate constant ( $k$ in Eqn. (3357)) for each reaction.

When third-body reactions are specified in a mechanism, the reaction is written with an additional species M as a reactant, a product, or both. Auxiliary information regarding enhanced third-body efficiencies of certain species is given on the line below the reaction. The names of the third-body species are followed by their enhancement factors.

Gas / Surface Thermodynamic Properties Files

Thermodynamic properties are given in state function data files for either seven-coefficient or nine-coefficient NASA polynomial form for each species:

Seven-coefficient NASA polynomial format

Line 1: The name of the species, the elemental composition of the species, three temperatures which define the temperature ranges over which the polynomial fits to thermodynamic data are valid. For example, the three temperatures (K) in the example below show the low temperature fit (298.000), the high temperature fit (5000.000), and the common temperature between these fits (1000.00).
Line 2-4: Fourteen polynomial coefficients are provided (seven coefficients, $a_{1}$ through $a_{7}$ , for two consecutive temperature ranges).

Nine-coefficient NASA polynomial format

For more information, see Using Thermodynamic Polynomial Data.

Gas Transport Properties Files

Gas phase transport properties are given (optionally) by a molecular data file which provides seven variables for each species in the mechanism:

chemical name
indicator for the structure of the species (0 = atom, 1 = linear molecule, 2 = non-linear molecule)
two parameters describing the shape of the Lennard-Jones potential well:
- well depth divided by Boltzmann’s constant [K]
- collision diameter [Å]—the (finite) distance at which the inter-particle potential is zero. (If you adjust this value, make sure that it realistically represents values given in literature for the specific material.)
the bond dipole moment [Debye]
the polarizability [Å3]
the rotational collision number (ZROT) at 298 K

Since the molecular data is species-specific, you can use any file which contains data for all species in the gas or solid state phase. Molecular data files are not tied to a specific kinetic scheme.

Surface Chemistry Reaction Files

Surface data files contain relevant solid state data and look much the same as gas phase data files. In addition it contains data for the material of the surface, the surface sites, and the site density.

Keywords

All Input Files

The following keywords are accepted in all types of input files.

BULK

Precedes lines with surface bulk species in the mechanism. You can specify this keyword immediately before a custom name for the bulk data.

ELEMENTS / ELEMENT / ELEM

Precedes lines with elements of the species in the mechanism.

END

Required on the line below the data which follows each of the above keywords.

MATERIAL

Precedes the name of the material that the subsequent surface data corresponds to. You can state more than one material, where each material is followed by material-specific surface data.

REACTIONS / REAC

Precedes lines with reaction data for all reactions in the mechanism.

To set the unit of $E_{a}$ in the mechanism, follow this keyword with one of:
- CAL/MOLE
- KCAL/MOLE
- JOULES/MOLE
- KELVINS
- EVOLTS
To set the unit of $A$ in the mechanism, follow this keyword with one of:
- MOLES
- MOLECULES

Units for $E_{a}$ and $A$ can be set on the same line. If no unit is specified, data is assumed to be given in cal/mole.

If you specify the unit of $A$ in the mechanism as MOLECULES, then upon importing the mechanism, the pre-exponential factors are converted to the moles unit system by the equation:

A_{j} (M O L E S) = A_{j} (M O L E C U L E S) \times {N_{A}}^{n - 1}

(279)

where:

$A_{j}$ is the pre-exponential factor of the $j$ th reaction
$N_{A}$ is the Avogadro number
$n$ is the sum of reactant stoichiometric coefficients, also referred to as the reactant order.

SDEN

Standard-state density for the site in units of moles/cm².

SITE

Precedes lines with surface species in the mechanism. SITE must be followed by the SDEN keyword.

You can specify this keyword immediately before a custom name for the site data.

SPECIES / SPEC

Precedes lines with species in the mechanism.

THERMO ALL

Same as THERMO but shows that all state functions data of the mechanism is found after the keyword and not in additional sections of the mechanism.

THERMO / THERM

Precedes lines with state function data in the mechanism.

Gas Input Files

The following keywords are only accepted in gas phase data input files.

DUPLICATE / DUP: If a reaction path can have multiple sets of reaction coefficients, follow each set by a line with this keyword.
FORD: In order to alter the forward rate of a specific reaction, you use this keyword on the line below the specific reaction, followed by a species name and reaction order. Specifying a reaction order in this way replaces existing reaction orders or adds new species and reaction orders to the reaction rate calculation.
HIGH: Placed on the line below a pressure-dependent, chemically activated bimolecular reaction, followed by reaction coefficients for the high-pressure limit: $A_{\infty}$ , $β_{\infty}$ , and $E_{\infty}$ in Eqn. (3378).
LOW: Placed on the line below a pressure dependent fall-off reaction, followed by reaction coefficients for the low-pressure limit: $A_{0}$ , $β_{0}$ , and $E_{0}$ in Eqn. (3377).
PLOG: Given after a reaction, this keyword is followed (within forward slashes) by its corresponding pressure ranges, in units of bar, with pre-exponential factors, temperature exponents, and activation energies in Eqn. (3384).
REV: For one-way reactions, you can specify this keyword on the line below a reaction followed by reaction data for the reverse reaction.
RORD: In order to alter the reverse (backwards) rate of a specific reaction, you use this keyword on the line below the specific reaction, followed by a species name and reaction order. Specifying a reaction order in this way replaces existing reaction orders or adds new species and reaction orders to the reaction rate calculation.
SRI: For SRI pressure dependent reactions, this keyword is placed on a separate line after the keywords LOW and HIGH. This keyword is followed by five parameters: $a$ , $b$ , $c$ , $d$ , and $e$ in Eqn. (3381).
TROE: For Troe pressure dependent reactions, this keyword is placed on a separate line after the keywords LOW and HIGH. This keyword is followed by four parameters: $α$ , $T^{*}$ , $T^{* *}$ , and $T^{* * *}$ in Eqn. (3380).

Surface Input Files

The following keywords are only accepted in surface data input files.

COV: This keyword followed by a species and three coverage parameters, $η_{i, j}$ , $μ_{i, j}$ , and $ε_{i, j}$ , modifies the forward reaction rate constant according to Eqn. (3399).
DUPLICATE / DUP: If a reaction path can have multiple sets of reaction coefficients, precede each set by a line with this keyword.
FORD: In order to alter the forward rate of a specific reaction, you use this keyword on the line below the specific reaction, followed by a species name and reaction order. Specifying a reaction order in this way replaces existing reaction orders or adds new species and reaction orders to the reaction rate calculation.
REV: For one-way reactions, you can specify this keyword on the line below a reaction followed by reaction data for the reverse reaction.
RORD: In order to alter the reverse (backwards) rate of a specific reaction, you use this keyword on the line below the specific reaction, followed by a species name and reaction order. Specifying a reaction order in this way replaces existing reaction orders or adds new species and reaction orders to the reaction rate calculation.
STICK: To use sticking coefficients instead of reaction coefficients, provide this keyword without parameters on the line below a reaction. Replace the reaction variables ( $A$ , $β$ , and $E_{a}$ in Eqn. (3365)) of the preceding reaction by sticking coefficients: $a_{i}$ , $b_{i}$ and $c_{i}$ in Eqn. (3400).