Excitations charge/spin

To use HyperChem for calculations, you specify the total molecular charge and spin multiplicity (see Charge, Spin, and Excited State on page 119). The calculation selects the appropriate many-electron wave function with the correct number of alpha or beta electrons. You don t need to specify the spin function of each orbital. 

The scheme indicated in Figure 1 (excitation, charge separation, charge recombination) is most likely to occur when the product state has the same spin multiplicity as the reactant state, or when the product species are held together (e.g., by chemical bonds) for periods that allow intersystem crossing to occur. However, the charge separation-recombination sequence is not the only type of process that photoexcitation can achieve. An example is when the product state is held only loosely by a solvent cage and the entities therein can diffuse apart and have independent reactive identities. Such a scheme would be typified by the sequence... 

This case occurs when we treat the singlet excited states of the vdW dimers and complexes (the so-called triplet-triplet (TT) excitations). The spin-correlator analysis for the vdW dimers was shortly mentioned in [61] where the singlet hssion models are discussed. In context of the EUE problems we can connect spin correlators with the Ngff measure of the TT-type excited states. For instance, when no charge transfer effects are involved, the local spins (S ) = (S ) provide an estimate... 

Self-localized excitation Chemical term Charge Spin... 

It is also interesting to note that although excitons are spinless quasiparticles, PL-ODMR of excitons still may show strong spin 1/2 and spin 1 resonances due to cross-recombination channels with other quasiparticles that do possess spins. It is quite common in PL-ODMR and ADMR spectroscopies that a spinless excitation may show magnetic resonances. Therefore, we should not discard the possibility that spinless excitations in conducting polymers [5 in t-(CH), and BP in NDGS polymers) can show spin 1/2 resonances. This does not mean that these charged excitations carry spin ... 

An important property of the dimerized Peierls stale is the existence of gaps in the spectra of spin and charge excitations. For free electrons (//ci-ci=0) both gaps are equal, while in the presence of Coulomb repulsion the spin gap is smaller than the charge gap [23, 24]. In what follows, we will assume the temperature to be much smaller than these two gaps, so that we can neglect electronic excitations and replace Hcl [ A (.v)] by its ground state expectation value. 

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