Landau–Zener model

Within the Born–Oppenheimer approximation, a semi-classical model for the probability, $P$ , of hopping from one electronic state to another of the same or different multiplicity

$P = exp ( − 4 π 2 ɛ 1 2 2 h v | s 1 − s 2 | )$

where $ɛ 1 2$ is the potential energy gap between the two electronic states at a surface crossing point, $| s 1 − s 2 |$ is the difference in slopes between the intersecting potential energy curves at this point and $v$ is the nuclear relative velocity with which the system passes the point of closest approach.

Note:

The original formalism only considered states of the same spin multiplicity.

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 362