Sudden polarization effect

The sudden-polarization effect falls somewhat outside the scope of this chapter, since it is confined to electronically excited states. However, since it may have... 

Separate optimization of the relevant function spaces zwitterionic excited states of polyenes and the sudden polarization effect... 

I.D. Petsalakis, G. Theodorakopoulos, C.A. Nicolaides, R.J. Buenker, S.D. Peyerimhoff, Nonorthonormal Cl for molecular excited states. I. The sudden polarization effect in 90° twisted ethylene, J. Chem. Phys. 81 (1984) 3161. 

Buenker, R. J., Bonacic Koutecky, V., Pogliani, L., Potential energy and Dipole moment Surfaces for Simultaneous Torsion and Pyramidalization of Ethylene in Its Lowest lying Singlet Excited States A Cl Study of the Sudden Polarization Effect, J. Chem. Phys. 1980,73, 1836 1849. 

The Intermediacy of highly polarizable forms (and possibly the effect of sudden polarization) next to blradlcalold species In the relaxation processes of excited trlenes (dienes and polyenes), their relative contributions depending on substitution pattern and medium. 

Polarization-transfer experiments which are based on a resonance condition, i.e. where a variable quantity in the experiment is matched to a parameter of the investigated spin system, can be carried out as a transient experiment or as an adiabatic experiment Figure 11.5 illustrates the differences between these two types of experiments. In a transient or sudden" experiment, the density operator is prepared in a state orthogonal to the effective polarization-transfer Hamiltonian (Fig. 11.5a). When the polarization-transfer Hamiltonian is switched on, the density operator starts precessing around the effective Hamiltonian, and usually maximum polarization transfer is reached after a 180° rotation. Since often the size of the effective Hamiltonian at the matching condition depends on... 

Consider first the polarization curve (i.e., Tafel plot) for the anodic halfreaction occurring in corrosion of stainless steels (Fig. 16.8). The diagram for the active region is much the same as has been seen for other anodes (Figs. 15.4 to 15.7). As Eh is increased to a certain specific value, however, a sudden and dramatic drop in the anodic current density i occurs, corresponding to formation of an oxide film. At higher Eh, i remains constant at a very low level (the horizontal scale in Fig. 16.8 is logarithmic), and the metal has become passive, that is, effectively immune from corrosion. 

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