Justin Yonker (Virginia Tech)
In spite of its status as a minor species, NO plays key roles in many upper atmospheric processes. As the only heteronuclear molecule, its fundamental, Delta v=1 emission cools the thermosphere (z>100 km). Its low ionization potential ensures that NO^+ is the end product of the ion-neutral chemistry in the ionospheric E-region. And in the presence of excess atomic oxygen, NO will catalytically destroy ozone. The production of NO is initiated when N_2 is ionized, dissociated, or excited by the solar EUV irradiance (lambda < 100 nm). In the mesosphere and lower thermosphere (MLT), much of the irradiance is contained in the highly variable soft x-ray region (1 < lambda < 20 nm). The resulting photoelectrons produce additional ionization as well as excitation of metastable, chemically-reactive species like the first electronically excited N_2 state, N_2(A^3 Sigma_u^+). This talk will incorporate recent laboratory data on the N_2 photoabsorption and electron-impact cross-sections into a 1D photochemical reaction-diffusion model of the thermosphere. It is shown that spin-forbidden (Delta S=1) excitation to the N_2 triplet manifold enables neutral N_2 to participate in the NO production. Additional physical and chemical uncertainties relevant to NO production and loss are also presented.