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The mechanism of the shift, broadening and quenching of the ammonia inversionfrequency with gas pressure has been a problem of lively interest for overseventy years. A simple quantum model of the ammonia molecule perturbed bycollisions with ideal gas molecules displays the essential features of theexperimental data for NH3 and for ND3. The model does not display the behaviourexpected from theories of quantum localisation such as quantum state diffusionand decoherence. On the other hand, models of perturbed classical oscillatorsdo display similar behaviour to our model. The quenching of the ammoniainversion transition cannot therefore be interpreted as spatial localisation ofthe wavefunction.

Quantum molecular dynamics study of the pressure dependence of the ammonia inversion transition