singlet–triplet crossing

https://doi.org/10.1351/goldbook.ST07477
Point of intersection between the potential energy surfaces of states of different multiplicity.
Note:
The intersection belongs to a ($$3\ N-7$$)-dimensional subspace of the ($$3\ N-6$$)-dimensional nuclear coordinate space and therefore appears as a line on a two-dimensional energy surface ($$N$$ is the number of nuclei). In this case the @[email protected] is one-dimensional and is defined by the @[email protected] difference vector $$x_{1}$$.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 421 [Terms] [Paper]