https://doi.org/10.1351/goldbook.CT07347

Point of crossing between two electronic states of the same spin multiplicity (most commonly singlets or triplets).**Notes: **

*Source: *

PAC, 2007,*79*, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 317 (https://doi.org/10.1351/pac200779030293)

- In a polyatomic molecule two @P04780@ are allowed to cross along a (3
*N*− 8)-dimensional subspace of the (3*N*− 6)-dimensional nuclear coordinate space (the @IT07400@) even if they have the same spatial/spin symmetry (*N*is the number of nuclei). Each point of the @IT07400@ corresponds to a conical intersection. If the energy is plotted against two special internal geometrical coordinates,*x*_{1}and*x*_{2}, which define the so-called @BT07335@, the potential energy surface would have the form of a double cone in the region surrounding the @D01556@. In the remaining (3*N*− 8) directions, the energies of the @G02704@ and @E02257@ remain degenerate; movement in the @BT07335@ lifts the @D01556@. - From a mechanistic point of view, conical intersections often provide the @C00970@ mediating @R05056@ and @P04585@. CT07347.png

PAC, 2007,