Ethylene excited state configuration

These results can be summarized as follows The triplet carbene ( 5i) adds nonstereospecifically because its complex and a ground state ethylene correlate with the triplet state of an excited trimethylene configuration, which has no barriers to rotation around terminal bonds. 

In order to understand the origin of the breakdown of the SR methods away from equilibrium, consider the torsional potential in ethylene (Figure 2). While at its equilibrium geometry ethylene is a well-behaved closed-shell molecule whose ground and n-valence excited states can be described accurately by SR models (except for the doubly excited Z-state), it becomes a diradical at the barrier, when the Jt-bond is completely broken (13). Thus, at the twisted geometry all of ethylene s Jt-valence states (N, T, V, and Z) are two-configurational, except for the high-spin components of the triplet. 

One example of non-IRC trajectory was reported for the photoisomerization of cA-stilbene.36,37 In this study trajectory calculations were started at stilbene in its first excited state. The initial stilbene structure was obtained at CIS/6-31G, and 2744 argon atoms were used as a model solvent with periodic boundary conditions. In order to save computational time, finite element interpolation method was used, in which all degrees of freedom were frozen except the central ethylenic torsional angle and the two adjacent phenyl torsional angles. The solvent was equilibrated around a fully rigid m-stilbene for 20 ps, and initial configurations were taken every 1 ps intervals from subsequent equilibration. The results of 800 trajectories revealed that, because of the excessive internal potential energy, the trajectories did not cross the barrier at the saddle point. Thus, the prerequisites for common concepts of reaction dynamics such TST or RRKM theory were not satisfied. 

Figure 2. Initially, in a thermal reaction, there are two electrons in each of the ethylene -orbitals, and it is apparent that if the reaction follows the symmetrical reaction path, the initial state correlates with a highly excited state of the product. Configuration interaction between the two Aig states leads to an avoided crossing, but there is still a considerable activation energy (Figure 3a). The thermal reaction is...

The ground-state configuration of the two-ethylene system is a b u (see Table 7-1). This state is totally symmetric, Ag. The excitation of an electron from the HOMO to the LUMO will give an electron configuration agbiub2u. The direct product is ... 

Figure 29.5. Ethylene. Configuration of tt electrons in ground state and excited state.

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