What is Born Oppenheimer Principle?

Answer 1

This is an approximation that is based on the fact that the electron is more than 1000 times lighter than the nucleus of the atom. It allows you to model the motion of electrons as being completely independent of the motion of nuclei because the motion of the nuclei is much much slower than that of electrons. For instance, when an molecule absorbs light such that its electronic configuration changes, that happens essentially immediately. Then the nuclei will move accordingly (either shortening or lengthening bond lengths for instance).

Answer 2

The Born-Oppenheimer approximation is a fundamental concept in quantum mechanics that allows the separation of nuclear and electronic motion in molecules. It assumes that the motion of atomic nuclei is much slower compared to the motion of electrons, allowing for the electrons to adjust instantaneously to changes in nuclear positions. This principle forms the basis for understanding molecular structure and spectroscopy.