CISS and a Phase Space Theory of Electronic Structure

The Born-Oppenheimer approximation is the cornerstone of chemistry, the idea that electronic structure and molecular orbitals are defined relative to a stationary set of coordinates for the nuclei. This premise is based on the important differences in mass between electrons and nuclei, and the all important fact that nuclei move much slower than electrons and appear effectively frozen on the time scale of electronic fluctuations. Nevertheless, it is known that the Born-Oppenheimer approximation breaks down quite often, quite famously in the context of photochemistry and/or electron transfer. Slightly less well known is the fact that a classical BO theory does not conserve momentum (linear or angular) even when there is no obvious breakdown. In this talk, I will discuss this failure of the BO approximation, offer up phase space approximations as an improvement to restore conservation, and then suggest a new paradigm for understanding how nuclear entanglement with electronic degrees of freedom may well lead to chiral induced spin selectivity (an exciting phenomenon discovered in recent years) and other magnetic field effects (including vibrational circular dichroism and raman optical activity).