New analysis of the ν6 band of H 2O 2: The ( n, τ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional subbands

Abstract

The ν 6 band of H 2O 2 has been recorded at a resolution of 0.002 cm −1 by means of Fourier transform spectroscopy in the spectral region 1190–1330 cm −1. The ( n, τ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional subbands have been extensively analyzed leading to a large and precise set of torsion-rotation energy levels for the v 6 = 1 vibrational state. Numerous resonances have been observed and are discussed. For the ( n, τ) = (0, 3), (1, 3) rotational levels the resonances are mainly due to the v 2 = 1 vibrational state whereas for the ( n, τ) = (0, 1), (1, 1), and (2, 1) rotational levels, the v 3 = 1 vibrational state and/or the ground state is also involved. For the ( n, τ) = (0, 3), and (1, 3) torsional states it has been possible to satisfactorily fit the experimental energies using a Hamiltonian which takes simultaneously into account both the interactions between the torsional states within the v 6 = 1 state and the v-off diagonal ( v 6 = 1 ↔ v 2 = 1) interaction between the levels of the v 6 = 1 and v 2 = 1 vibrational states. As very few data are available concerning the v 3 = 1 vibrational state it has not been possible to perform a similar calculation for the ( n, τ) = (0, 1), (1, 1), and (2, 1) torsional states and the least-squares fit was performed taking into account only the resonances within the v 6 = 1 state and neglecting the resonances with the other vibrational states. Finally, using the ( n, τ) = (0, 1), (1, 1), (2, 1), (0, 3), and (1, 3) torsional band centers the cis- and trans-barrier heights of the v 6 = 1 vibrational state have been estimated.