Structure of the Alkali Hydroxides. V. The Infrared Spectra of Matrix-Isolated RbOH, RbOD, NaOH, and NaOD

Abstract

The infrared spectra of matrix‐isolated RbOH, RbOD, NaOH, and NaOD have been observed. Both the alkali‐metal–oxygen stretch ${\nu }_1$ and the bending mode ${\nu }_2$ have been assigned for each species. The metal–oxygen stretching mode is found at 354.4, 345, 431, and 422 cm⁻¹ for RbOH, RbOD, NaOH, and NaOD, respectively; the bending mode ${\nu }_2$ is observed at 309.0, 229, 337, and 250 cm⁻¹, respectively. Combination of the results of this study with the microwave measurements for RbOH and RbOD indicates an essentially linear structure for these species. The isotope shift for ${\nu }_2$ observed in NaOH coupled with reasonable bond lengths indicates an equilibrium configuration of NaOH which probably does not deviate significantly from linearity. The assumption of a linear model with a harmonic bending potential yields force constants of 0.046 × 10⁻¹⁸ and 0.053 × 10⁻¹⁸ Nm (0.046 and 0.053 mdyn·Å) for RbOH and NaOH, respectively. These results are consistent with our previously reported results for CsOH.