Knowledge Bank

High resolution spectra of $H2O2$, recorded by means of Fourier transform spectroscopy between 30 and $460cm-1$ have been analysed leading to the determination of the rotational levels of the torsional states $(n,\tau )$ for $n=0,1,2,3$. To reproduce these energy levels. Watson type Hamiltonians have been used and it has been possible to observe the staggering of the levels due to the cis-barrier for n=2 and 3. The torsional hand centers have then been fitted using a torsional Hamiltonian of the form $\{B\gamma \gamma ,J\gamma 2\}+V(\gamma )$ with the potential energy function $V(\gamma )$ written as $V(\gamma )=V1\cos 2\gamma +V2\cos 4\gamma +V3\cos 6\gamma +V4\cos 8\gamma$ where the torsional coordinate $2\gamma$ is the dihedral angle defining the relative position of the two O-H honds. The potential function constants obtained are $V1=1036.97\pm 23.1cm-1,V2=657.53\pm 5.2cm-1.V3=50.89\pm 3.3cm-1,V4=2.524\pm 0.83cm-1$$ corresponding to the barrier heights $Vtrans=387.07\pm 0.20cm-1VCIs=2563\pm 70cm-1$$ and to potential energy minima located at $2\gamma =111.9.\pm 0.4$ from the cis-configuration. It is also shown that the rotational constants derived through the fit of the experimental rotational levels cannot be reproduced using a model which does not take into account the vibrational corrections.