Knowledge Bank

J. T. $Hougen1$ has shown that hydrogen peroxide may be effectively classified as having $C2h$ symmetry. A symmetry based notation which greatly simplifies the description and treatment of $H2O2$ will be introduced. Using capital letters for overall symmetry, successive torsional states in an A vibrational state, including the ground state, are labeled 0G, 0U, 1G, 1U, 2G, etc. In vibrations of symmetry B, the U and G labels are interchanged. Symmetry allowed transitions are , and symmetry allowed perturbations are and . Rotational constants of the 0G and 1G torsional states and the matrix element coupling these states have been determined by least squares fitting of combination differences obtained from submillimeter spectra and Fourier transform spectra of the anti-symmetric O-H stretching band, $\nu 5$, and the associated hot band and sum band involving the 1G torsional state. Several series of forbidden transitions provide precise energy differences between the coupled torsional states. The model used for the fitting was an S-reduction Hamiltonian of two asymmetric rotors coupled by a $\Delta K=2$ interaction. The 1G torsional state is at $254.54931cm-1$. The corresponding torsional mode in the $\nu 5$ and $\nu 2+\nu 6$ vibrational states is about 11 cm higher. Values will be given for the 0U - 0G torsional splitting in the $\nu 1,\nu 5,\nu 2+\nu 6,2\nu 2$, and $2\nu 6$ vibrational states.