Interaction of Molecules
Polar molecules, which have a permanent electronic dipole moment, interact via dipole-dipole forces at large intermolecular separations. However, van der Waals forces at shorter separations and chemical interactions when the electronic clouds overlap can prevail. This is particularly true when molecules can come close together as, for example, is true in optical and magnetic traps.
In PRL 100, 203201 (2008) we studied inelastic collisions between RbCs molecules with their constituent atoms for a number of individual vibrational levels. The van der Waals coefficients between molecules and atoms were found from their dynamic polarizability at imaginary frequencies. We also used a quantum scattering model, which solely relies on an isotropic van der Waals coefficient to obtain scattering rates and collisional lifetimes of ultracold molecules. The agreement between our predictions and the experimental observations at Yale University is good.
We are currently working towards development of a new model, which will involve the determination of the strength and vibrational dependence of both short- and long-range interactions between molecules. For rotating polar molecules, where the dipole-dipole interaction does play a role and the van der Waals potential is anisotropic (depends on the relative orientation of the molecules) we propose to perform close coupling calculations, where multiple rotational states of the molecule are coupled by these interactions.