Infrared Spectrum of Solid and Matrix-Isolated H2O2 and D2O2

Abstract

The infrared spectrum between 4000 and 200 cm⁻¹ of polycrystalline D₂O₂ at − 190°C corresponds to that of H₂O₂ indicating that the crystal structure and spiral chain coupling of excitons for each of the six normal modes are the same in D₂O₂ as in H₂O₂. At temperatures near − 100°C the crystal spectra of both H₂O₂ and D₂O₂ change with time on CsI and CsBr cold windows. The greatest change observed is that the crystal bands arising from torsion disappear and are replaced by two other bands about 100 cm⁻¹ lower in frequency. Also, the exciton bands in the stretching and bending regions lose their fine structure and shift to lower frequency indicating that the peroxides actually dissolve into the salt windows without decomposition at these low temperatures. The spectra of H₂O₂ and D₂O₂ matrix isolated in argon and nitrogen at about 8°K are also reported. The most interesting features of these spectra are the extraordinarily broad bands in the torsional region, ${\nu }_4$ , in both nitrogen and argon. The relative intensities of the triplet in argon are observed to change reversibly with temperature. In argon matrices, spectra of the torsional region indicate that the motion of the peroxide in the cavity is similar to that in the gas phase. The techniques of earlier workers for analysis of hindered internal rotation were applied to calculate energy levels for the matrix‐isolated molecule. In argon the triplet in the torsion band is explained in terms of combination sum and difference bands of the internal rotation with translational or librational modes. In a nitrogen matrix, the spectra indicate that the internal rotation is much more hindered. The breadth of the band is explained in terms of a coupling between the hindered internal rotation and translation and/or librational motion as well as combination sum and difference bands with these motions.