Residence times transition complex

This investigation is exploratory, so it affords no evidence which discloses the undoubtedly complex mechanisms underlying the observed effects. However, it seems reasonable to assume that a time-dependent catalytic effect exists which is related to the composition and temperature of the hot zone surface to which the arc sample effluent was exposed. The rapid transition in hydrocarbon composition from acetylene to methane in the presence of iron or stainless steel is one indication. Thermal effects and increased residence time in the presence of hydrogen lead to progressive diminution and disappearance of hydrocarbons, suggesting another, slower process which may be pyrolytic or possibly inhibitory. 

Density fimctional theory (DFT) studies of the series of complexes [Cr(L)(H20)5]" (where L = Ns, NO, NS, or NSe) show that the unpaired electron resides in a metal-based dxy orbital and that the electronic structure in the equatorial plane is similar in all four complexes and resembles Cr. The a donating ability was formd to follow the order Ns NO < NS NSe, whereas the n accepting ability followed the order NO>NSsiNSe. Time dependent DFT calculations gave in all four complexes a d, 2 3,2 —d transition energy arormd 17,500 cm (123). 

Full ab initio treatments for complex transition metal systems are difficult owing to the expense of accurately simulating all of the electronic states of the metal. Much of the chemistry that we are interested in, however, is localized around the valence band. The basis functions used to describe the core electronic states can thus be reduced in order to save on CPU time. The two approximations that are typically used to simplify the basis functions are the frozen core and the pseudopotential approximations. In the frozen core approximations, the electrons which reside in the core states are combined with the nuclei and frozen in the SCF. Only the valence states are optimized. The assumption here is that the chemistry predominantly takes place through interactions with the valence states. The pseudopotential approach is similar. 

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