The reaction between photogenerated NO2 radicals and a superoxochromium(III) complex, CraqOO2+, occurs with rate constants k(Cr)(20) = (2.8 +/- 0.2) x 10(8) M-1 s(-1) (20 vol% acetonitrile in water) and k(Cr)(40) = (2.6 +/- 0.5) x 10(8) M-1 s(-1) (40 vol % acetonitrile) in aerated acidic solutions and ambient temperature. The product was deduced to be a peroxynitrato complex, CraqOONO22+, which undergoes homolytic cleavage of an N-O bond to return to the starting materials, the rate constants in the two solvent mixtures being k(H)(20) = 172 +/- 4 s(-1) and k(H)(40) = 197 +/- 7 s(-1). NO2 reacts rapidly with 10-methyl-9,10-dihydroacridine, k(A)(20) 2.2 x 10(7) M-1 s(-1), k(A)(40) = (9.4 +/- 0.2) x 10(6) M-1 s(-1), and with N,N,N',N'-tetramethylphenylenediamine, k(T)(40) = (1.84 +/- 0.03) x 10(8) M-1 s(-1).