Vibronic and exciton–phonon interaction in <i>α</i>-nitrogen crystals
Abstract
The intensity distribution and form of the bands of the absorption spectrum of nitrogen crystals in the region 1500−1200 Å at 6 °K are measured. The electronic-vibrational series constants and the parameters of the interaction of the electron excitation with totally symmetrical intramolecular phonons for the weak transitions αʹπg←XʹΣg+ and ωʹΔu←XʹΣg+ are determined. The single-particle nature of the vibronic excitations and the contribution of the Herzberg–Teller interaction to the intensity are established. In analyzing the structure of separate bands induced by the coupling with crystalline phonons, effects due to the competition between bands and localized states are observed. It is shown that the observed changes in the asymmetry and width of bands as a function of the vibron number can be described in the intermediate exciton-phonon coupling approximation. The width of the exciton bands and the signs of the effective masses of the excitons of the a and w states are estimated.