Spin-forbidden substitution

Three different mechanisms were considered (i) direct spin-forbidden addition of CO (ii) spin-state change from 3Fe(CO)3 (H2) to 1Fe(CO)3(H2) or 1Fe(CO)3(H)2, followed by rapid addition of CO and (iii) spin-allowed substitution reaction between CO and 3Fe(CO)3(H2) to give 3Fe(C0)4 and H2, followed by spin-forbidden addition of H2 to 3Fe(C0)4. The results are summarized in Table V. 

The only difference from the single-channel EM outlined above (Section V.A) is the substitution of k et by the sum of the spin-allowed and spin-forbidden transfer rates k et + k c, to the ground and triplet states, respectively. Like k-eh the intersystem crossing rate kKC does not depend on viscosity. Moreover, EM does not separate the two different steps of the forbidden transition spin conversion to the triplet RIP and subsequent allowed electron transfer into the triplet product [212-216]. However, as has been shown in Section XI.A, even in the case of a single channel but spin-forbidden reaction (I), one should discriminate between the spin conversion and subsequent recombination through electron transfer. The qualitative difference between the spin-allowed and... 

This is exactly the same result as for the spin-forbidden recombination from the triplet precursor, but with kt substituted for kc in Eq. (3.577) and for 1 according to the rates and the weights of the reacting states. As a result, (p(r) = 1/(1 + Z/D), and Z(r) has the same properties as its analog studied in the previous subsection ... 

Typical transition metal complexes with a partially filled d-shell at the metal are characterized by low-energy dd (or ligand field, LF) states [8]. Frequently, these dd states are not luminescent but reactive [9-13]. Ligands are then substituted because LF states are often antibonding with respect to metal-ligand interactions. Nevertheless, a considerable number of transition metal compounds with emissive LF excited states are known. However, in many cases this luminescence appears only at low temperatures. Moreover, spin selection rules are not strictly obeyed, in particular by metals of the second and third transition series. Intersystem crossing is then facifitated and the rate of spin-forbidden emission (phosphorescence) is increased. As a consequence a phosphorescence may also be observed at room temperature. 

The reaction of 2a with N2 is predicted by DFT calculations to be strongly endothermic, while that of 2b is predicted to be exothermic, indicating a large destabilization of the carbene with respect to the diazo compound by the fluorine substitution. Despite this, the thermal reaction between 2b and N2 could not be observed, presumably because of a thermal activation barrier for this formally spin-forbidden reaction. The reaction of both carbenes 2a and 2b with CO to give the corresponding ketenes, on the other hand, proceeds rapidly on annealing CO-doped argon matrices. [48]... 

There are a few green Tb -based phosphors, suitable for application in fluorescent lamps. Despite intensive research, no substitute for Y203 Eu with the same spectral properties has been found, leaving it the only red primary with line emission at about 611 nm. The width and position of the emission bands originating from optical transitions within the f-electronic shell are almost independent of the chemical environment. The relative intensity of the separate bands, however, depends on the crystal lattice. The transitions on many rare-earth ions are spin- and parity-forbidden and therefore rather slow (in the ms range). However, for a number of rare-earth ions, broad emission bands are also known, due to d f emission, e.g. 

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