Spectroscopic and Reactive Minima in Excited-State Surfaces

3 Spectroscopic and Reactive Minima in Excited-State Surfaces 

POTENTIAL ENERGY SURFACES BARRIERS, MINIMA, AND FUNNELS 

we consider the two simplest and most fundamental cases of biradicaloid geometries, reached from ordinary geometries by stretching a single bond or by twisting a double bond. These two cases together underlie much of organic photochemistry. 

Unlike the biradicaloid minima located along the dissociation path of a a bond, one of which occurred at a loose (T,) and one at a tight (S,) geometry, those located along the dissociation path of a jr bond are at nearly the same geometry. The reason for this difference can be readily understood in terms of the simple model of biradicaloid states outlined in Section 4.3. 

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