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tokens: (Note that this model is therefore agnostic to the light curve, but we included such a light curve in the fiducial flare for use in time-dependent models.) The impulsive model tracks the absorption and scattering of the flare photons and terminates when all photons have been either absorbed within the atmosphere, absorbed by the ground (assumed to be perfectly absorbing), or exited the top of the atmosphere (scattered out). The result represents an upper limit on the dissociation of various species: in reality, recombination reactions will be happening during any true flare, reducing the maximum quantities of dissociated species. However, an exception to this could occur if secondary reactions amplify dissociation, such as catalytic destruction of O 3 by NO x species. We use the inactive star fiducial flare model of Section 7 to set the spectral content of the flare input. The modeled atmosphere is that of Earth (1 bar surface pressure) and receives a bolometric flux equivalent to Earth’s insolation. We consider only the substellar point in the atmosphere. Its compositional profile is a combination of several empirical models of Earth’s atmosphere covering different height regimes and including different constituents: 1. NRLMSISE-00 (Picone et al. 2002 ) is a global atmospheric model commonly used for engineering purposes. We use it to specify N 2 , O 2 , O, H, N, Ar, and He densities from 0 to 1000 km. 2. NASA Earth GRAM 2016 24 24 https://software.nasa.gov/software/MFS-32780-2 is a goal atmospheric model intended for environmental science. We use it to specify H 2 O, O 3 , CO 2 , CO, CH 4 , and N 2 O densities from 0 to 1000 km. 3. Hu et al. ( 2012 ) compiled atmospheric data from multiple sources on a variety of trace species to validate the general purpose atmospheric photochemistry model they developed. We use their profiles to specify OH, NO, and NO 2 densities from 0 to 80 km. H 2 and O( 1 D) were included purely as dissociation products. We use a grid of 400 layers, with thicknesses of 0.5 km up to 100 km and 4.5 km up to the top of the model at 1000 km. The high upper boundary to the model allows important resonant scattering by atomic H and O to be included. This yields scattering columns of 2.9 × 10 13 H and 8.5 × 10 17 O atoms cm −2 above 100 km (300 nbar) and 1.1 × 10 14 H and 1.1 × 10 18 O atoms cm −2 at ground level. Figure 21 shows the state of the atmosphere before and after exposure to flares of three representative equivalent durations. The δ = 10 4 s flare is akin to the largest observed in this survey, whereas the δ = 10 8 s flare is likely about an order of magnitude less energetic than the largest M dwarf flare observed to date (the DG CVn flare described by Osten et al. 2016 ; see Section 3.4 ). The effects progress from negligible to dramatic over this range. At the highest energy, the atmosphere exhibits clear dissociation fronts among the different species. A potentially surprising feature is the increase in CO