The far infrared spectrum of H2O2. First observation of the staggering of the levels and determination of the c i s barrier

Abstract

High resolution spectra of H₂O₂, recorded by means of Fourier transform spectroscopy between 30 and 460 cm⁻¹, have been analyzed leading to the determination of the rotational levels of the torsional states (n,τ) for n=0,1,2,3. In order to reproduce these energy levels, Watson type Hamiltonians have been used and it has been possible to observe a staggering of the levels with n=2 and 3 caused by the cis barrier. The torsional band centers have then been fitted using a torsional Hamiltonian of the form {B_γγ,J²_γ} +V(γ) with the potential function V(γ) written as V(γ)=V₁ cos 2γ+V₂ cos 4γ+V₃ cos 6γ+V₄ cos 8γ where the torsional coordinate 2γ is the dihedral angle defining the relative position of the two O–H bonds. The potential constants in cm⁻¹ are V₁=1036.97±23.1 cm⁻¹, V₂=657.53±5.2 cm⁻¹, V₃=50.89±3.3 cm⁻¹, V₄=2.524±0.83 cm⁻¹ which correspond to barrier heights V_trans =387.07±0.20 cm⁻¹, V_cis =2562.8±60 cm⁻¹, and to a potential minimum located at 2γ=111.9°±0.4° from the cis configuration. It is also shown that the rotational constants derived from the fit to the experimental rotational levels cannot be reproduced using a model which does not take into account vibrational corrections.