Infrared Spectrum of Matrix-Isolated Nitrate Ion

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Abstract
The infrared spectra of the nitrate ion isolated in KI, KBr, KCl, NaBr, and NaCl matrices have been examined in the 4000–400 cm−1 region and analyzed. The results indicated that the site symmetry of such a nitrate ion is C3ν. Some anharmonicity constants have been determined, and they were found to be essentially independent of the matrix. The harmonic frequencies, on the other hand, were shifted to higher frequencies as the lattice constant of the matrix was decreased. The fundamental bands showed Lorentz band shapes, and the temperature dependence of their bandwidths allowed an estimation of the potential barrier to reorientation of the nitrate ion in the host matrix. In the KI matrix, bands assignable to combinations of an internal vibrational mode with localized lattice modes have also been observed.