Interaction of molecular rotation with large-amplitude internal motions: A rigid twister model of hydrogen peroxide

The classical dynamics of interaction between molecular rotation and large-amplitude internal rotation is studied for a rigid twister model of hydrogen peroxide, obtained by assuming an adiabatic separation of the torsional degree of freedom from the remaining 3N - 7 vibrational modes. Use of the Augustin-Miller canonical transformation to express the molecule-fixed components of the total angular momentum j in terms of the magnitude, j, the component along the body-fixed z axis, k, and x, the angle conjugate to k, results in a two degree of freedom rotation-torsion Hamiltonian, whose phase space structure can be characterized by using surfaces of section. Rigid twister surfaces of section are presented for several values of angular momentum and energy. Quasi-periodic trapping and crossing tori are found, together with regions of large-scale rotation-torsion chaos. The effects of deuteriation and variation of torsional barrier heights on phase space structure are investigated. Removing either the centrifugal or Coriolis coupling terms from the rigid twister Hamiltonian leads to a significant increase in stochasticity; we infer that there is a cancellation of coupling terms in the full Hamiltonian.