Triplet State of the Nitrite Molecule–Ion

The absorption spectra of aqueous solutions of a number of nitrite complexes exhibit a common absorption band at ∼ 23 kK. This absorption band is responsible for the color of those metal nitrites in which the cation is colorless. This band is assigned as the T1 ← S0 transition of the nitrite molecule–ion. The intensification of the T1 ← S0 transition in the heavier-metal nitrites is a spin–orbit enhancement brought about by the heavy-metal cation. Equilibrium constants for Cd(II), Pb(II), and Tl(I) nitrite complexes- and extinction coefficients for the 23-kK band have been elicited. The 23-kK band is the reverse absorption to the phosphorescence emission; the T1 → S0 radiative lifetimes correlate with those calculated from oscillator strengths of the 23-kK absorption band.