Quantum Zeno Effect in a Model Multilevel Molecule

We study the dynamics of the populations of a model molecule endowed with two sets of rotational levels of different parity, whose ground levels are energetically degenerate and coupled by a constant interaction. The relaxation rate from one set of levels to the other one has an interesting dependence on the average collision frequency of the molecules in the gas. This is interpreted as a quantum Zeno effect due to the decoherence effects provoked by the molecular collisions.