title: Interaction induced localization in a gas of pyramidal molecules.
abstract: We propose a model to describe a gas of pyramidal molecules interacting via dipole-dipole interactions. The interaction modifies the tunneling properties between the classical equilibrium configurations of the single molecule and, for sufficiently high pressure, the molecules become localized in these classical configurations. We explain quantitatively, without free parameters, the shift to zero frequency of the inversion line observed upon increase of the pressure in a gas of ammonia or deuterated ammonia. For sufficiently high pressures, our model suggests the existence of a super-selection rule for states of different chirality in substituted derivatives.
authors.affiliation: Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, Roma 00185, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Jona-Lasinio
authors.forename: Carlo
authors.initials: C
authors.lastname: Presilla
authors.forename: Cristina
authors.initials: C
authors.lastname: Toninelli