Theory of Cold Atomic and Molecular Collisions

Mariusz Pawlak, Yuval Shagam, Ayelet Klein +2 more

We recently developed an adiabatic theory for cold molecular collision experiments. In our previous application of this theory (Pawlak, M.; et al. J. Chem. Phys. 2015, 143, 074114), we assumed that during the experiment the collision of an atom with a diatom takes place when the diatom is in the ground rotational state and is located in a plane. In this paper, we present how the variational approach of the adiabatic theory for low-temperature collision experiments can be used for the study a 5D collision between the atom and the diatomic molecule with no limitations on its rotational quantum states and no plane restrictions. Moreover, we show here the dramatic differences in the measured reaction rates of He(2 3 S 1 ) + ortho / para -H 2 → He(1s 2 ) + ortho / para -H 2 + + e – resulting from the anisotropic long-range interactions in the reaction. In collisions of metastable helium with molecular hydrogen in the ground rotational state, the isotropic potential term dominates the dynamics. When the collision is with molecular hydrogen in the first excited rotational state, the nonisotropic interactions play an important role in the dynamics. The agreement of our results with the latest experimental findings ( Klein, A.; et al. Nat. Phys. 2017, 13, 35−38) is very good.

Marius Lysebo

Arpita Rakshit, Bimalendu Deb

We discuss theoretically ion-atom collisions at low energy and predict the possibility of the formation of a cold molecular ion by photoassociation. We present results from radiative homo- and heteronuclear atom-ion cold collisions that reveal threshold behavior of atom-ion systems.

Paul S. Julienne

Bimalendu Deb

In the preceding four chapters, we have mainly described the fundamentals of formal scattering theory at low energy. In this chapter, we apply this theory to cold atomic collisions. We first discuss the applications to atomic scattering in the absence and then in the presence of an external field. In the millikelvin or submillikelvin temperature regime, atomic hyperfine (HF) interactions—that is, interactions between the nuclear and electronic spins of an atom—become important in atomic collisions, even in the absence of any external field, because the energy scale associated with the HF interaction is typically on the order of 100 mK. Therefore, to understand low-energy atomic collisions, it is instructive to begin with a general introduction to atomic HF interactions. It is also essential to have a basic understanding of the origin and the method of constructing diatomic molecular potentials to understand low-energy atomic scattering from first principles. A detailed discussion of these topics, which would require some knowledge of atomic and molecular structure, is beyond the scope of this book.

F. W. Sohon