Electronic spectra and structure of 1- and 2-fluoronaphthalene impurity centers in crystalline naphthalene
M.D. Curmei, V. I. Melnyk, G. V. Klishevich, T. V. Bezrodna, V. V. Nesprava,and O. M. Roshchin
Institute of Physics of the National Academy of Sciences of Ukraine, Kyiv 03028, Ukraine
Received January 20, 2021 , published online March 26, 2021
The results of experimental investigations on the low-temperature fluorescence and absorption spectra of the 1- and 2-fluoronaphthalene impurities in the crystalline naphthalene are presented and analyzed. When the 1- and 2-fluoronaphthalene concentrations are less than 1%, the absorption and fluorescence spectra are shown to be composed of two identical band series, induced by the formation of two different centers, consisting of the single impurity molecules. The impurity concentration increase of over 1% results in the appearance of the additional structure in the polarized absorption spectra near the 0-0 bands of the single centers in a form of narrow bands with similar intensity and different polarization. This structure is associated with a formation of impurity paired centers, consisting of the two resonantly interacting molecules of either1-fluoronaphthalene, or 2-fluoronaphthalene. Besides, in the case of the 2-fluoronaphthalene, the absorptionspectra contain intense peaks, located ~45 cm–1 higher in frequency, relative to the 0–0 transition bands for eachsingle-center, and consisted of complexes of narrow lines. These spectral peaks are also explained by a formation of impurity paired centers, but here interactions between the molecules are not resonant. For the purenaphthalene crystal factors, causing the observation of additional oppositely polarized weak bands in the absorption spectra at ~10 cm–1 near the Davydov doublet components, are described.
Key words:  Davydov splitting; impurity paired centers; wavetrain; 1-, 2-fluoronaphthalene.