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Branched(Wennberg NO + RO2 Reaction)#

Wennberg NO + RO2 reactions are branched 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 \((\mathrm{molecules}\ \mathrm{cm}^{-3})\), \(X\) 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 \((\alpha_0, n)\):

\[Z(\alpha_0, n) = A(T = 293 K, [M] = 2.45 \times 10^{19} \frac{\text{molec}}{\text{cm}^3}, n) \frac{(1-α_0)}{α_0}\]

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

Input data for Wennberg NO + RO2 equations has the following format:

type: WENNBERG_NO_RO2
X: 123.45
Y: 1200.0
a0: 1.0e8
n: 6
time unit: MIN
reactants:
    spec1:
    spec2:
      qty: 2
alkoxy products:
    spec3:
    spec4:
      yield: 0.65
nitrate products:
    spec5:
    spec6:
      yield: 0.32

{
    "type" : "WENNBERG_NO_RO2",
    "X" : 123.45,
    "Y"  : 1200.0,
    "a0"  : 1.0e8,
    "n" : 6,
    "time unit" : "MIN",
    "reactants" : {
      "spec1" : {},
      "spec2" : { "qty" : 2 },
    },
    "alkoxy products" : {
      "spec3" : {},
      "spec4" : { "yield" : 0.65 },
    },
    "nitrate products" : {
      "spec5" : {},
      "spec6" : { "yield" : 0.32 },
    }
}

The key-value pairs reactants, alkoxy products, and nitrate products are required. Reactants without a qty value are assumed to appear once in the reaction equation. Products without a specified yield are assumed to have a yield of 1.0.

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. The unit for time is assumed to be s, but inclusion of the optional key-value pair time unit = MIN can be used to indicate a rate with min as the time unit.

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