Influence of resonance interactions and matrix environment on the spectra of SF(6) dimers in low-temperature nitrogen matrixes. Theory and experiment.

The IR absorption spectra of (SF(6))(2) dimers were studied in N(2) matrixes at 11 K. Absorption bands due to SF(6) monomers and to (SF(6))(2) dimers have been identified. As a result of the resonance dipole-dipole interaction between two SF(6) subunits, the band of the triply degenerate vibration nu(3) is split into two components nu(X),(Y) and nu(Z), where Z is the axis connecting the two sulfur atoms. The main distinction between the spectra of (SF(6))(2) dimers recorded here compared to spectra in the gas phase is the splitting of the nu(X),(Y) component. 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 including the resonance interactions, (ii) determine with the help of the Monte Carlo method the structure of a matrix consisting of 864 N(2) molecules and a rigid (SF(6))(2) dimer, and (iii) take into account the interactions of local dipole moments of a dimer with host particles in the approximation of dipole-induced dipole and dipole-quadrupole interactions. The calculated spectra sufficiently well reproduce the main characteristics of the experimental spectra in N(2) matrixes, in particular, the decrease of the resonance splitting upon transition from the gas phase to a matrix and the splitting of nu(X,Y) component in the nitrogen matrix.