Potential-energy surfaces solid-state structures

There is evidently a flat potential energy surface for these clusters as different skeletal isomers can actually be isolated in the solid state for Au9[P(C6H40Me)3]8(N03)3 a brown form has a D4d crown structure and a green form has a D2h structure. In solution, however, they share a common structure with identical31P NMR spectra either the solution cluster has a regular arrangement of phosphines, or it is fluxional [186]. 

Potential energy surfaces or profiles are descriptions of reactions at the molecular level. In practice, experimental observations are usually of the behaviour of very large numbers of molecules in solid, liquid, gas or solution phases. The link between molecular descriptions and macroscopic measurements is provided by transition state theory, whose premise is that activated complexes which form from reactants are in equilibrium with the reactants, both in quantity and in distribution of internal energies, so that the conventional relationships of thermodynamics can be applied to the hypothetical assembly of transition structures. 

Fig. 8 On the left is the Cr(CO)3 potential energy surface topology traversed after photodissociation of Cr(CO)6 to the conical intersection of the S2 and S0 states at D3h symmetry. The right hand side shows the branching space at the D conical intersection. The pseudorotation coordinate is shown connecting the C4y geometries through a C2y transition structure. The D3(i symmetry is indicted by the gray circle, the transition states by open circles while the three equivalent C4v species are indicated are indicted with solid circles. Adapted from [17]...

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