Triplet State of the Nitrite Molecule–Ion

Abstract

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 $T_1{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}S}}_0$ transition of the nitrite molecule–ion. The intensification of the $T_1{\mathrm{\hspace{0.17em}\leftarrow \hspace{0.17em}S}}_0$ 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 $T_1{\mathrm{\hspace{0.17em}\to \hspace{0.17em}S}}_0$ radiative lifetimes correlate with those calculated from oscillator strengths of the 23‐kK absorption band.