Opening-mode bending

The thermal decomposition of ammonium rho-zeolites- has also been followed by inelastic and quasielastic neutron scattering [112]. As the deammoniation temperature was increased, the assigned vibrational features of the bound ammonium ion at 1452 cm (bending modes), 306-363 cm" (ammonium-coupled pore-opening modes of the zeolite framework), and 80-113 cm" (hindered rotational modes) were foimd to diminish with the emergence of scattering features due to H-rho. 

Also, our normal coordinate analysis revealed that the Cr-CO-, ring-Cr-C-and the C-Cr-C-bending coordinates are strongly coupled in E symmetry. In AI symmetry, the C-Cr-C umbrella opening mode is coupled with the Cr-C-O parallel bend. For details of the assignments the reader is referred to Table 12, in which we also included mode descriptions based on the criterion of potential energy distribution. The frequency related to the B2U C-C stretching vibration is overestimated, as it is for free benzene and for BzaCr. 

One reason that the symmetric stretch is favored over the asymmetric one might be the overall process, which is electron transfer. This means that most of the END trajectories show a nonvanishing probability for electron transfer and as a result the dominant forces try to open the bond angle during the collision toward a linear structure of HjO. In this way, the totally symmetric bending mode is dynamically promoted, which couples to the symmetric stretch, but not to the asymmetric one. 

Fig. 9.38 (a) Measured upper panel) and calculated lower panel) NIS spectra of the HS open circle, dashed line) and the LS filled triangle, solid line) isomer (1 meV = 8.06 cm ) of [Fe (phen)2(NCS)2]. (b) Calculated contributions A5vib(i) of individual modes i to the vibrational entropy difference bars, left axis) and sum I /ASyib (i) of the contributions of modes 1 to i filled circle, right axis). The 15 modes of an idealized octahedron (six Fe-N stretching modes and nine N-Fe-N bending modes) are marked by the letters s and b, respectively. (Taken from [44])... 

Fermi resonances of the v0H=l state with over- and combination tones of modes in the fingerprint region are considered a key element determining the spectral envelope of the O-H stretching bands of cyclic carboxylic acid dimers. In principle, such Fermi resonances open up channels for population relaxation of the O-H stretching modes through the O-H bending... 

The typical features of an open chain anhydride are shown in the spectrum of acetic anhydride (Fig. 3.34). It is also worth noting in this spectrum the very weak C—H stretching band for the methyl group, and the much enhanced intensity of the symmetric C—H bending mode when attached to a carbonyl group. 

Fig. 10.5. Measured rotational state distributions of OH following the dissociation of the three lowest bending states of H2O (open circles). In addition to the bending quanta H20(X) also contains 4 respectively 3 quanta of OH stretching excitation. The local mode nomenclature nm k) is explained in Section 13.2. The total angular momentum is zero in all cases. The filled circles represent the harmonic oscillator approximation defined in the text. Reproduced from Schinke, Vander Wal, Scott, and Crim (1991).

Formation of these products is rationalized in terms of suprafacial addition of the elements of Pd—Cl to a ring that is opening stereospecifically in a disrotatory mode, with the breaking bond bending away from the metal (dis-out) (equation 326). The absence of rj to rj to rj interconversions between the isomeric complexes is rationalized in terms of a severe steric blocking of the anti (to metal) allylic face of the complex by the nine-membered ring. This is evident from X-ray crystal structure analysis of the mononuclear acetylaceto-nate allylic complex obtained from chloropalladation of the cw-bicyclononane ". ... 

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