Infrared Spectrum of Matrix-Isolated Cyanate Ion. I. Vibrational Analysis, Bandwidths, and Absolute Intensities in Potassium Halides

Abstract

Solid solutions of the cyanate ion in KCl, KBr, and KI matrices have been prepared by heating standard infrared pressed disks. The infrared spectra of these disks have been measured from 5000 to 400 cm⁻¹ and analyzed. Our frequency data are in excellent agreement with those obtained from doped single crystals by earlier investigators. Anharmonicity constants, harmonic frequencies, and force constants have been calculated for the isotopic species ¹⁶O¹²C¹⁴N⁻, ¹⁶O¹²C¹⁵N⁻, ¹⁶O¹³C¹⁴N⁻, ¹⁶O¹³C¹⁵N⁻, and ¹⁸O¹²C¹⁴⁻. The anharmonicity constants are essentially independent of the matrix, and only quadratic force‐constant changes appear necessary to account for the frequency shifts of the fundamentals as the matrix is varied. The temperature dependence of the bandwidths and peak frequencies of the fundamentals have been studied in the range from 95 to 530°K. The fundamentals in all matrices can be represented well by Lorentz band shapes. The absolute band intensities have also been measured. In addition to bands arising from the internal modes of the cyanate ion, combination bands of the intense cyanate fundamentals with external modes of the cyanate and with lattice modes of the host matrix have been observed.