Reactions

The fields common to all reaction entries are:

equation

The stoichiometric equation for the reaction. Each term (i.e., stoichiometric coefficient, species name, + or <=>) in the equation must be separated by a space.

Reversible reactions may be written using <=> or = to separate reactants and products. Irreversible reacions are written using =>.

type

A string specifying the type of reaction or rate coefficient parameterization. The default is elementary. Reaction types are:

Reactions on surfaces or edges are automatically treated as interface reactions, and reactions that involve charge transfer between phases are automatically treated as electrochemical reactions, without the need to specify the type.

duplicate

Boolean indicating whether the reaction is a known duplicate of another reaction. The default is false.

orders

An optional mapping of species to explicit reaction orders to use. Reaction orders for reactant species not explicitly mentioned are taken to be their respective stoichiometric coefficients. See Reaction orders for additional information.

negative-orders

Boolean indicating whether negative reaction orders are allowed. The default is false.

nonreactant-orders

Boolean indicating whether orders for non-reactant species are allowed. The default is false.

Depending on the reaction type, other fields may be necessary to specify the rate of the reaction.

Arrhenius expression

Arrhenius expressions can be specified as either a three-element list containing the pre-exponential factor \(A\), the temperature exponent \(b\), and the activation energy \(E_a\), or a mapping containing the fields A, b, and Ea. The following are equivalent:

{A: -2.70000E+13 cm^3/mol/s, b: 0, Ea: 355 cal/mol}
[-2.70000E+13 cm^3/mol/s, 0, 355 cal/mol]

Efficiencies

Some reaction types include parameters for the “efficiency” of different species as third-body colliders. For these reactions, the following additional fields are supported:

efficiencies

A mapping of species names to efficiency values

default-efficiency

The efficiency for use for species not included in the efficiencies mapping. Defaults to 1.0.

Reaction types

elementary

A homogeneous reaction with a pressure-independent rate coefficient and mass action kinetics, as described here.

Additional fields are:

rate-constant

An Arrhenius-type list or mapping.

negative-A

A boolean indicating whether a negative value for the pre-exponential factor is allowed. The default is false.

Example:

equation: N + NO <=> N2 + O
rate-constant: {A: -2.70000E+13 cm^3/mol/s, b: 0, Ea: 355 cal/mol}
negative-A: true

three-body

A three body reaction as described here.

The reaction equation should include the third body collision partner M.

Includes the fields of an elementary reaction, plus the fields for specifying efficiencies.

Example:

equation: 2 O + M = O2 + M
type: three-body
rate-constant: [1.20000E+17 cm^6/mol^2/s, -1, 0]
efficiencies: {AR: 0.83, H2O: 5}

falloff

A falloff reaction as described here.

The reaction equation should include the pressure-dependent third body collision partner (+M) or (+name) where name is the name of a species. The latter case is equivalent to setting the efficiency for name to 1 and the efficiency for all other species to 0.

Includes field for specifying efficiencies as well as:

high-P-rate-constant

An Arrhenius expression expression for the high-pressure limit

low-P-rate-constant

An Arrhenius expression expression for the low-pressure limit

Troe

Parameters for the Troe falloff function. A mapping containing the keys A, T3, T1 and optionally T2. The default value for T2 is 0.

SRI

Parameters for the SRI falloff function. A mapping containing the keys A, B, C, and optionally D and E. The default values for D and E are 1.0 and 0.0, respectively.

Example:

equation: H + CH2 (+ N2) <=> CH3 (+N2)
type: falloff
high-P-rate-constant: [6.00000E+14 cm^3/mol/s, 0, 0]
low-P-rate-constant: {A: 1.04000E+26 cm^6/mol^2/s, b: -2.76, Ea: 1600}
Troe: {A: 0.562, T3: 91, T1: 5836}

chemically-activated

A chemically activated reaction as described here.

The parameters are the same as for falloff reactions.

Example:

equation: CH3 + OH (+M) <=> CH2O + H2 (+M)
type: chemically-activated
high-P-rate-constant: [5.88E-14, 6.721, -3022.227]
low-P-rate-constant: [282320.078, 1.46878, -3270.56495]

pressure-dependent-Arrhenius

A pressure-dependent reaction using multiple Arrhenius expressions as described here.

The only additional field in this reaction type is:

rate-constants

A list of mappings, where each mapping is the mapping form of an Arrhenius expression expression with the addition of a pressure P.

Example:

equation: H + CH4 <=> H2 + CH3
type: pressure-dependent-Arrhenius
rate-constants:
- {P: 0.039474 atm, A: 2.720000e+09 cm^3/mol/s, b: 1.2, Ea: 6834.0}
- {P: 1.0 atm, A: 1.260000e+20, b: -1.83, Ea: 15003.0}
- {P: 1.0 atm, A: 1.230000e+04, b: 2.68, Ea: 6335.0}
- {P: 1.01325 MPa, A: 1.680000e+16, b: -0.6, Ea: 14754.0}

Chebyshev

A reaction parameterized as a bivariate Chebyshev polynomial as described here.

Additional fields are:

temperature-range

A list of two values specifying the minimum and maximum temperatures at which the rate constant is valid

pressure-range

A list of two values specifying the minimum and maximum pressures at which the rate constant is valid

data

A list of lists containing the Chebyshev coefficients

Example:

equation: CH4 <=> CH3 + H
type: Chebyshev
temperature-range: [290, 3000]
pressure-range: [0.0098692326671601278 atm, 98.692326671601279 atm]
data: [[-1.44280e+01,  2.59970e-01, -2.24320e-02, -2.78700e-03],
       [ 2.20630e+01,  4.88090e-01, -3.96430e-02, -5.48110e-03],
       [-2.32940e-01,  4.01900e-01, -2.60730e-02, -5.04860e-03],
       [-2.93660e-01,  2.85680e-01, -9.33730e-03, -4.01020e-03],
       [-2.26210e-01,  1.69190e-01,  4.85810e-03, -2.38030e-03],
       [-1.43220e-01,  7.71110e-02,  1.27080e-02, -6.41540e-04]]

interface

A reaction occuring on a surface between two bulk phases, or along an edge at the intersection of two surfaces, as described here.

Includes the fields of an elementary reaction plus:

sticking-coefficient

An Arrhenius-type expression for the sticking coefficient

Motz-Wise

A boolean applicable to sticking reactions, indicating whether to use the Motz-Wise correction factor for sticking coefficients near unity. Defaults to false.

sticking-species

The name of the sticking species. Required for sticking reactions only if the reaction includes multiple non-surface species.

coverage-dependencies

A mapping of species names to coverage dependence parameters, where these parameters are contained in a mapping with the fields:

a

Coefficient for exponential dependence on the coverage

m

Power-law exponent of coverage dependence

E

Activation energy dependence on coverage

Example:

equation: 2 H(s) => H2 + 2 Pt(s)
rate-constant: {A: 3.7e21 cm^2/mol/s, b: 0, Ea: 67400 J/mol}
coverage-dependencies: {H(s): {a: 0, m: 0, E: -6000 J/mol}}

electrochemical

Interface reactions involving charge transfer between phases, as described here.

Includes the fields of an interface reaction, plus:

beta

The symmetry factor for the reaction. Default is 0.5.

exchange-current-density-formulation

Set to true if the rate constant parameterizes the exchange current density. Default is false.

Example:

equation: LiC6 <=> Li+(e) + C6
rate-constant: [5.74, 0.0, 0.0]
beta: 0.4