Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

A second-order version of this effect was derived by Opik and Price and results from mixing between states, while determining the adiabatic potential energy surface for systems undergoing this effect leads to the "Mexican Hat" potential. UV-vis spectra for systems undergoing it show splitting of bands, and this effect explains the structure of the cyclooctatriene anion. This phenomenon is responsible for the sharp vertical transition line between low-spin and high-spin states in some Tanabe-Sugano diagrams, and another version of this effect occurs because orbital angular momentum defines the parity of the wavefunction in linear molecules, a version partly named for Renner. It occurs most strongly in systems in which the e sub g orbitals are unevenly occupied, forcing them into a lower energy state. For 10 points, name this effect in which a molecule is distorted in order to break degeneracy and lower energy.
Science