Broken Symmetry States of Rotating Molecules in Solids

Abstract

The excited states of molecules rotating in solids are of two kinds. Like the s states of the hydrogen atom the symmetric kind exhibits the full symmetry of the Hamiltonian and like the p states the broken symmetry kind does not. Since the standard quantum discussion of molecular rotation omits all except symmetric states and the classical hopping model reflects the properties of broken symmetry states, the two theories have been incompatible. We show that if the quantum discussion includes all states the two theories are perfectly compatible and we demonstrate experimentally the existence of the broken symmetry states through the differential broadening of nmr level crossing transitions of a tunnelling NH₄ ion.