Bending, high-frequency

Variational RRKM theory is particularly important for imimolecular dissociation reactions, in which vibrational modes of the reactant molecule become translations and rotations in the products [22]. For CH —> CHg+H dissociation there are tlnee vibrational modes of this type, i.e. the C—H stretch which is the reaction coordinate and the two degenerate H—CH bends, which first transfomi from high-frequency to low-frequency vibrations and then hindered rotors as the H—C bond ruptures. These latter two degrees of freedom are called transitional modes [24,25]. C2Hg 2CH3 dissociation has five transitional modes, i.e. two pairs of degenerate CH rocking/rotational motions and the CH torsion. 

Complexation of a C02 carbon with a free radical is a possibility, but intrinsic frequencies as high as 2346.6 cm "1 have been observed in spectra of ABP at temperatures where radical pairs have already collapsed. This does not disprove the existence of complexation in Species A1 for example, but it does show that high frequency bands can occur in the absence of radicals. Spectra of v2 provide some evidence for complexation, but analogous effects on v3 spectra have not been observed. For example, Semple has found an abnormally low bending frequency in early spectra of bis(ll-chloro-undecanoyl) peroxide, suggesting complexation between the carbon of C02 and a primary radical, but the stretching band shows no unusual shift to high frequency (T. G. Semple, personal communication). These observations are commensurate with measurements on H20 and NH3 complexes of C02 discussed in Section IV.C.3.b. 

The different diagonal Hamiltonians H. ree, HBend. and H°, dealing, respectively, with the high frequency mode, the bending mode, and the H-bond bridge may be assumed to be the non-Hermitean ones given in Table IX, in which the zero-point... 

Eq.(297). For simplicity, we are here limit to the special case of two Fermi resonances and the situation where the indirect damping is missing and where the direct damping of the first excited state of the high frequency mode is the same as those of the first harmonics of the two bending modes. Then, the Hamiltonian (297) reduces to... 

The rate constants for electron transfer and recombination are readily separated because in the limit (w- 0), equation (8.31) tends to kir/(ktr + krec), and the maximum of the semicircle occurs when ca = 2ir f=kt + krec. In the absence of RC attenuation effects, the high frequency intercept of the IMPS plot (minority carriers. Measurements of gac as a function of potential (band bending) can be used to determine the minority carrier lifetime and absorption coefficient [46]. The main advantage of using the IMPS data rather than dc measurements of... 

The low frequency bridge bending vibration vp is not degenerate in this case and has two components of slighly different frequency. This leads to two series of hot bands which overlap and, especially at the high frequency side of v1( smear out the structure. In Fig. 10 taken from Thomas 79) the first six hot band origins are marked. The interpretation of the fine structure leads to 145 and 170 cm-1 for the two components of vp while v can be estimated to be 180 cm-1 and the enthalpy of association AH° = —26 kJ mol-1. 

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