Side bands of the vibrational spectrum of interstitial elements in a metal lattice

The dynamics of oxygen atoms in Ta-O solid solution has been studied by the slow-neutron inelastic scattering method. Indications have been obtained for the existence of vibration-rotation excitations of an interstitial atom in a metal lattice. In addition to the peaks corresponding to the fundamental oscillations of a harmonic oscillator (ℏω_1,2 ≈ 42 meV and ℏω₃ ≈ 82 meV), side bands with an energy of ɛ ≈ ℏω₃ ± 6 meV are observed in the atomic oxygen spectrum. Analysis of the spectral structure leads to the assumption that the observed satellites are attributed to vibration-rotation excitations of an impurity oxygen atom in the field of metal atoms surrounding it. The oxygen atom is probably displaced in the basal plane from the center of the octahedral interstice of the crystal lattice and can freely move along a slightly corrugated energy channel around the geometric center of the octahedron. The energy position of the side bands are in good agreement with the excitation energies estimated in the model of the superposition of two circular motions of the oxygen atom in the basal plane of the tantalum lattice near the center of the octahedral interstice.