that the reason for this behavior is the low value of the vibrational frequencies in the transition state of this step, 7. It appears as well that the high frequencies in the reactant structure favor a fast rate.23 Thus, in reactions where rearrangements occur before groups are lost, Le., in multiple-step processes, it is difficult to perform any RRKM calculation giving reliable information without having an accurate knowledge of the potential surface, and the related parameters.Kinetic Energy Release. In a unimolecular dissociation, the kinetic energy release (KZR) may have two contribution^:^^ Te, the KER due to a potential energy barrier (reverse activation energy), and T*, the KER associated with the nonfixed energy, or excess energy. Baer et aI.l3 have obtained at a photon energy of 13.6 eV (3.8 eV above the products 4) an average kinetic energy release of 0.74 eV, which corresponds to 19.5% of the total energy. A statistical distribution of the rvailable energy among the vibrational, rotational, and translational degrees of freedom can be calculated by25where R and {v,] are the number of rotational degrees of freedom and the vibrational frequencies of the products, respectively. 'The translational energy is just kT, where T i s calculated from eq 3 from an available energy E above products 4. The statistical distribution obtained in this way gives 5.3% of the available energy. The result is in agreement with Baer's calculation, with assumed vibrational frequencies for the products (CSH6+' + c o ) . This value is much lower than the experimental one (19.5%), showing that in reaction 1 kinetic energy release is not distributed statiscally.The reproduction of the KER would be important since it would be a test of the transition-state and the product structures. Recently, an approximate method to determine the KER in terms of the transition-state reaction coordinate has been developed by Derrick et In this method, the proportion of the reverse (23) To obtain insight into the role of the vibrational frequencies in the rate constant, we are carrying out a study on the system C6H5X+./C6DSX+' -C6H5+/C6D5+ + X , where the relative rates will be mainly determined by vibrational effects.(24) R. G.activation energy converted in translational energy is given by26a (4) where PS refers to three independent products separation motions, and R C refers to the direction of the reaction coordinate in the transition-state geometry. The uRC vector corresponds to the mass-weighted atomic displacements vector associated with the imaginary frequency of the transition state. By this technique, the calculated relation between F and the reverse activation energy is 47%, at 13.6 eV; the available energy for the products 4 is 2.41 eV, where 0.51 eV is the reverse activation energy and 1.90 eV is the nonfixed energy. The translational energy coming from the nonfixed energy can be estimated by partitioning the energy among all degrees of freedom.26b The three translational degrees would mean a fraction 3/N, N being the number of interna...

A systematic study has been made on the influence of doped rare-earth metal ions (E? and Nd3+) on the molecular interaction present in thin films fabricated from chitosan-acetic acid solutions (chitosan/HAc). FT-IR spectroscopy (including NIR, MIR and FIR) coupled with X-ray photoelectron spectroscopy (XPS) indicate a weak complexation between the metal ions and amine groups of chitosan. Specifically, the FIR spectra show broad bands near 550, 480 and 250 cm-' for the doped films suggestive of metal ion-ligand vibrations. XPS indicates multiple chemical states of N with an increased percentage of a higher binding energy state nitrogen caused by a weak interaction with the doped metal ions. Slight differences in microroughness between the doped and undoped films as observed by X-ray reflectometry may also be related to the doping. The NIR and MIR spectra do not show any significant changes for all the doped and undoped films, implying that the basic molecular conformation of chitosan is not changed by the weak complexation.

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