Branched NO + RO2 Reaction#

Branched reactions are typically used for NO + RO2 reactions with one branch forming alkoxy radicals plus NO2 and the other forming organic nitrates [WBC+18]. The rate constants for each branch are based on an Arrhenius rate constant and a temperature- and structure-dependent branching ratio calculated as:

\[k_{\text{nitrate}} = (X e^{-Y/T}) \left(\frac{A(T, [\text{M}], n)}{A(T, [\text{M}], n) + Z}\right)\]
\[k_{\text{alkoxy}} = (X e^{-Y/T})\left(\frac{Z}{Z + A(T, [\text{M}], n)}\right)\]
\[A(T, [\text{M}], n) = \frac{2 \times 10^{-22} e^n [\text{M}]}{1 + \frac{2 \times 10^{-22} e^n [\text{M}]}{0.43(T/298)^{-8}}} 0.41^{(1+[\log( \frac{2 \times 10^{-22} e^n [\text{M}]}{0.43(T/298)^{-8}})]^2)^{-1}}\]

where \(T\) is temperature \((\mathrm{K})\), \([\mathrm{M}]\) is the number density of air \((\mathrm{mol}\ \mathrm{m}^{-3})\), \(X\) and \(Y\) are Arrhenius parameters for the overall reaction, \(n\) is the number of heavy atoms in the RO2 reacting species (excluding the peroxy moiety), and \(Z\) is defined as a function of two parameters \((\alpha_0, n)\):

\[Z(\alpha_0, n) = A(T = 293 K, [M] = 40.6832 \frac{\text{mol}}{\text{m}^3}, n) \frac{(1-α_0)}{α_0}\]

More details can be found in Wennberg et al. (2018) [WBC+18].

Input data for Branched reactions have the following format:

type: BRANCHED_NO_RO2
name: foo-branched
X: 123.45
Y: 1200.0
a0: 1.0e8
n: 6
gas phase: gas
reactants:
  - species name: foo
    coefficient: 2.0
  - species name: bar
alkoxy products:
  - species name: baz
  - species name: qux
    coefficient: 0.65
nitrate products:
  - species name: corge
  - species name: grault
    coefficient: 0.32

{
    "type": "BRANCHED_NO_RO2",
    "name": "foo-branched",
    "X": 123.45,
    "Y": 1200.0,
    "a0": 1.0e8,
    "n": 6,
    "gas phase": "gas",
    "reactants": [
        {"species name": "foo", "coefficient": 2.0},
        {"species name": "bar"}
    ],
    "alkoxy products": [
        {"species name": "baz"},
        {"species name": "qux", "coefficient": 0.65}
    ],
    "nitrate products": [
        {"species name": "corge"},
        {"species name": "grault", "coefficient": 0.32}
    ]
}

The key-value pairs reactants, alkoxy products, and nitrate products are required. If coefficient is not specified for a reactant or product, it is assumed to be 1.0.

The gas phase key is required and must be set to the name of the phase the reaction takes place in. Each reactant and product must be present in the specified phase.

When X is not included, it is assumed to be 1.0, when Y is not included, it is assumed to be 0.0 K, when a0 is not included, it is assumed to be 1.0, and when n is not included, it is assumed to be 0.

Rate constants are in units of \(\mathrm{(m^{3}\ mol^{-1})^{(n-1)}\ s^{-1}}\) where \(n\) is the total number of reactants.

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