MOLECULES - CLASSICAL OBJECTS IN A QUANTUM-THEORY

Chemists are used to interpreting chemistry on the basis of at most a few molecules, although experiments are always carried out with macros copic amounts of substances only. We first give a weak but pragmatic d efinition of the notion of molecule. Then we show that molecules and t he chemical bodies mentioned above are two essentially different conce pts that do not emerge from one another by a mere scale factor as the Avogadro constant. This is the deeper reason that molecules and chemic al bodies have to be described within different theoretical frameworks . The line of demarcation between these two different kinds of objects , however, is as difficult to draw as the distinction of the scope of quantum mechanics and its classical analog, respectively. It will turn out that molecules are substantially classical objects because they a ctually possess an internal spatial structure of a certain temporal st ability. Therefore, the way molecules are usually described requires a tailor-made (chemical) version of quantum mechanics that rests on an extended separability theorem. The role of both superselection rules a nd EPR (Einstein-Podolsky-Rosen) correlations will be probed separatel y.