Raman and Vibronic Spectra of a New Oxygen Molecule Ion in CaF2

Abstract

AbstractSpectra are reported of an unidentified oxygen molecule center of monoclinic symmetry found in natural crystals of CaF2. Two alternative models consisting of a perturbed O and a O molecule ion substituting for two fluorine neighbors are discussed. In contrast to the well‐known unperturbed O center in CaF2, this new center has a visible absorption band. This band exhibits vibronic structure corresponding to an excited‐state vibrational frequency of (900 ± 10) cm−1 and coupling constants S ≈ 6 for this vibration and S ≧ 6 for the lattice phonons. This structure is enhanced in stress‐induced dichroism spectra. Resonance Raman scattering excited in this band shows the ground‐state vibrational fundamental at (1038 ± 1) cm−1 and the overtone at (2076 ± 2) cm−1. The polarization of these features is consistent with the 〈100〉 orientation of the center. The Lorentzian line‐shape, the width, and the relative intensity of the two‐ and one‐phonon scattering peaks are consistent with recent theories of the resonant Raman effect of impurity centers.