Phonon Side Bands of the Triplet Absorption in NaNO₂

Abstract

Absorption spectra of NaNO₂ associated with the electronic transition ¹A₁→³B₁ in NO₂⁻ have been measured for the E⁄⁄a, b and c polarizations. The E⁄⁄b and E⁄⁄c spectra show the series of vibronic lines accompanied with the phonon side bands, while the E⁄⁄a absorption is too weak to be observed. The selection rules are discussed for the modes of phonons which interact with the triplet exciton to give rise to the phonon side band of each polarization. The assignments are given to the prominent peaks and shoulders in the side bands of the E⁄⁄b and E⁄⁄c spectra. Two extra series of weak satellite bands have been found on the low energy tails of the vibronic lines and they are interpreted as the lines due to the isotopic species N¹⁴O¹⁶O¹⁸⁻ and N¹⁵O₂¹⁶⁻.