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The Primary Photodynamics of Aqueous Nitrate: Formation of Peroxynitrite

2003; American Chemical Society; Volume: 125; Issue: 50 Linguagem: Inglês

10.1021/ja030135f

1943-2984

Dorte Madsen, Jane Larsen, Svend Knak Jensen, S. R. Keiding, Jan Thøgersen,

Atmospheric chemistry and aerosols

We have examined the photochemical reactions occurring after irradiation at 200 nm of the aqueous nitrate ion, NO3(-)(aq). Using femtosecond transient absorption spectroscopy over the range 194-388 nm, we have characterized the formation and subsequent relaxation of the primary photoproducts of nitrate photolysis. The dominant photoproduct is the cis-isomer of peroxynitrite, which accounts for 48% of the excited state molecules initially produced. A slightly smaller fraction, 44%, of the excited molecules return to the electronic ground state of NO3(-) and relax to the vibrational ground state in 2 ps. The remaining 8% of the molecules initially excited react via the *NO + *O2(-) or the NO- + O2 dissociation channels. Formation of NO2(-) and *NO2 is not observed, suggesting that the previous observations of these species in steady-state photolysis are caused by reactions occurring on a longer time scale.