Vibrational spectra and intermolecular forces of 1,3,5,-trioxane and 1,3,5,7-tetroxocane crystals

Abstract

Polarized infrared and Raman spectra of 1,3,5‐trioxane (CH₂O)₃ and 1,3,5,7‐tetroxocane (CH₂O)₄ crystals have been measured. The correlation field splittings for the E vibrations of the trigonal cell of trioxane have been detected by measuring polarized Raman spectra on a single‐crystal specimen. The observed polarization properties of the infrared and Raman bands of tetroxocane single crystal have been interpreted by the crystal structure. The optically active lattice vibrations of the two crystals have been detected in the far‐infrared and/or Raman spectra. The normal mode calculations have been performed for the three‐dimensional crystal lattices by using the valence‐force‐field intramolecular forces and the van der Waals intermolecular interactions for the atomic pairs of H⋅⋅⋅H, O⋅⋅⋅H, C⋅⋅⋅H, O⋅⋅⋅O, C⋅⋅⋅O, and C⋅⋅⋅C. The parameters of the Lennard‐Jones type potential functions have been adjusted so as to reproduce the observed lattice mode frequencies by the least‐squares method and compared with the values permitted empirically by previous workers.