Infrared spectra of cis- and trans-peroxynitrite anion, OONO-, in solid argon

The peroxynitrite anion, of vast importance in biochemistry, is formed in vivo from the reaction of NO and O(-2). Laser ablation of 10 different metal targets with concurrent 7 K codeposition of NO/Ar and O(2)/Ar mixtures gives new metal-independent infrared bands at 1458.3 and 806.1 cm(-)(1), and at 1433.3 and 983.2 cm(-1), in addition to known O(-4) and (NO)(-2) absorptions. The new bands are not observed with CCl(4) added to capture electrons or in O(2) and NO experiments without laser ablation to produce electrons, which identifies new product anions. Based on (15)NO and (18)O(2) isotopic shifts, splitting patterns in mixed isotopic experiments, and comparison with DFT isotopic frequency calculations, the former absorptions are assigned to cis-OONO-, and the latter pair to trans-OONO-, which are isolated from metal cations trapped elsewhere in the matrix. The cis- and trans-peroxynitrite anion isomers are probably formed via the ion-molecule reaction between O(-2)and NO: the O(-2) anion, made by the capture of ablated electrons, is attested by the observation of O(-4). cis- and trans-OONO- are reversibly photoisomerized by visible and near-UV radiation. Collisional stabilization of the OONO- ion-molecule dimer complex during formation of the solid argon matrix appears to be crucial.