Vibrational Spectra of Molecular Metal Nitrate Monomers and Dimers

The infrared spectra of the matrix‐isolated vapors from hot samples of lithium, sodium, potassium, rubidium, thallium, and copper (II) nitrates are reported. The spectra are simple and clearly indicate that the dominant species in each case is the monomer of the metal nitrate, although limited decomposition could not be avoided with LiNO₃. Features indicative of the dimer, (MNO₃)₂, were also apparent for the alkali‐metal nitrates. Further, Raman bands have been detected for the ${\nu }_1$ modes of the isolated potassium and copper nitrates. The monomers seemingly represent the extreme of anion distortion for each case since the nitrate ion experiences the electrostatic field of a single closely associated cation. Thus, a comparison of the ${\nu }_3\mathrm{(e)}$ distortion splitting with that observed for cases for which the nitrate ion has been used as an environmental probe was of interest. Additional physical insight has been gained by relating the ${\nu }_3\mathrm{(e)}$ splittings to force constant variations in the anion, and, ultimately, to cation polarizing powers.