Events in Physics

Quenching of the Inversion Transition of Ammonia - A Classical or Quantum Problem?

In chemistry, molecules have spatial configurations while in physics they do not. Getting from the physics to the chemistry is an example of the problem of measurement, or Schroedinger's cat. Ammonia appears to bridge the gap, being physical at low pressure (as evidenced by its inversion transition) and chemical at high pressure. Consequently, the behaviour of the inversion transition has been a problem of lively interest for over seventy years. We will describe a simple quantum model of the ammonia molecule. Perturbed by collisions with ideal gas molecules, its time evolution is an problem in stochastic mechanics which we address by numerical calculation. The model does not display the behaviour expected from quantum-mechanical theories, but it does display the essential features of the experimental data. To understand this better, we have constructed purely classical models of perturbed oscillators and these do display behaviour similar to our model and to experimental data. However, predicting the behaviour of these stochastic models from their specifications appears to be an unsolved mathematicial problem.