Persistent infrared spectral hole burning of NO_2^− and NO_3^− ions in potassium iodide: II Spectral changes far from the burn frequency

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Abstract
We combine persistent IR spectral hole burning with high-resolution Fourier-transform interferometry to observe IR spectral changes far from the laser burn frequency for NO2− and NO3− ions in KI single crystals. Three separate vibrational mode types are investigated, and information about the symmetries of the modes is obtained. First the technique is used to separate isotopically modified and mixed stretch modes. Isotopedependent complex structures in the NO2− v1− and [v1 + v3]-mode regions appear to arise because of resonances between v1 and [V3 + phonon sideband] modes. Phonon-gap-mode sidebands on the NO2− V3 mode are examined and compared with results from far-infrared and Raman scattering studies. The number of resolved KI:NO2− gap modes is increased to five, and the translational and librational character of these modes is discussed in terms of their symmetry assignments. Defect-cluster lines of NO2− are hole burned, and many related satellite lines are observed to change. New assignments for NO2− :NO2− defect pairs and lines belonging to single NO2− defects associated with near-neighbor alkali or halide defects are made. Satellite lines of NO3− are also found to hole burn, and changes in these modes produce changes in additional NO2− satellite lines. Hence defect clusters involving both NO2− and NO3− ions are identified also.