The effect of resonance interactions on the absorption spectra of (SF₆)₂ dimers in low-temperature matrices: Calculations and experiment

Abstract

The IR absorption spectra of (SF₆)₂ dimers in Ar and N₂ matrices are investigated at 11 K. As a result of the resonance dipole-dipole interaction, the band of the triply degenerate vibration v ₃ is split into two components v _{X, Y} and v _Z. In comparison with the gaseous state, the splitting Δv = v _{X, Y} − v _Z in the argon matrix decreases to 18.45 cm⁻¹, whereas, in the nitrogen matrix, the band v _{X, Y} is split into components v _X and v _Y, with the splitting being equal to δ ≈ 0.9 cm⁻¹. A model that takes into account the influence of the matrix on the spectra of dimers is developed. The model makes it possible to successively (i) calculate the resonance spectrum of an isolated dimer in terms of the model of local modes taking into account resonance interactions, (ii) determine with the help of the Monte Carlo method the structure of a matrix consisting of 512–1440 Ar (or N₂) atoms and a rigid (SF₆)₂ dimer, and (iii) take into account interactions of local dipole moments of a dimer with particles of the matrix in the approximation of dipole-induced dipole interactions. The model developed satisfactorily describes the experimental results. The calculated frequencies v _Z, v _X, and v _Y of a dimer in the matrix are shifted toward smaller frequencies as compared to the gaseous state, while the resonance splitting decreases virtually by 2 cm⁻¹. It is shown that, in an argon matrix with a symmetric arrangement of argon atoms nearest to a dimer, the splitting of v _{X, Y} proves to be smaller than 0.05 cm⁻¹. In a nitrogen matrix, this splitting increases virtually to 0.4 cm⁻¹.