Vibrational spectrum of chlorine heptoxide

Abstract

The infrared and Raman spectra of chlorine heptoxide, Cl2O7, have been recorded in the vapor, liquid, and solid phases. The fundamental vibrations, with the exception of the two torsional modes, have been assigned under C2 symmetry. The resulting assignment leads to a near degeneracy of the skeletal stretches near 700 cm−1, and places the skeletal bending mode at 154 cm−1. A normal coordinate analysis has been carried out for Cl2O7 and related ClO3 group-containing molecules. Similarities in the skeletal stretching force constants (KR≃ 3 mdyn/ Å) and in the Cl–O bond lengths of Cl2O and Cl2O7 suggest that bonding is substantially the same in both molecules, thus implying a Cl–O single bond in the skeleton of Cl2O7. Thermodynamic properties of Cl2O7 have been calculated using torsional frequencies estimated from mean amplitudes of vibration.