Interaction of molecular rotation with large-amplitude internal motions: a rigid twister model of hydrogen peroxide
The Journal of Physical Chemistry
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 anguler momentum j in terms of the magnitude, j , the component along the body-fixed z axis, k, and x, the
... xis, 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. C. J. Chem. Phys. 1972,57, 332. 2914. 12. 83, 190. Chem. Phys. 1795. 82, 3083. 3809. Schranz, H. W.; Troe, J. Matrix isolation infrared spectroscopy applied to the ethylene oxide/H(D)I system trapped in solid Ar and Nz allows identification of several kinds of hydrogen-bonded complexes: a 1:l species which exists under two different structures and larger aggregates giving rise to proton transfer with formation of ionic species of the type [(EO),H]+ or (1HI)-characterized by quasi-symmetrical single-minimum potential functions for the proton (proton sharing). The interconversion between the hydrogen-bonded (C) and the non-hydrogen-bonded (U) forms of the 1:l complex is seen to depend on two parameters: temperature and infrared irradiation. Kinetic measurements of the disappearance (or appearance) of C have shown that the C -U conversion is mainly induced by IR radiations in the range 1500-2300 cm-I, corresponding to the excitation of us (HI stretching mode), while the C -U transformation is thermally induced above 17 K. From the temperature dependence of the kinetic rate constant an activation energy for C -U conversion has been obtained. The effect of HI/DI isotopic substitution is also discussed. The very slow C -U conversion rate with DI suggests a barrier greater than 1500 cm-I for this photoprocess.