Interaction of rotationally cold molecules with external fields

Timur V. Tscherbul, Roman V. Krems

Svetlana Kotochigova

Erik Abrahamsson, Timur V. Tscherbul, Roman V. Krems

The authors present a detailed study of low-temperature collisions between CaD molecules and He atoms in superimposed electric and magnetic fields with arbitrary orientations. Electric fields do not interact with the electron spin of the molecules directly but modify their rotational structure and, consequently, the spin-rotation interactions. The authors examine molecular Stark and Zeeman energy levels as functions of the angle between the fields and show that rotating fields may induce and shift avoided crossings between the Zeeman levels of the rotationally ground and rotationally excited states of the molecule. The dynamics of molecular collisions are extremely sensitive to external fields near these avoided crossings and it is shown that molecular collisions may be controlled by varying both the strength and the relative orientation of the fields. The effects observed in this study are due to interactions of the isolated molecules with external fields so the conclusions should be relevant for collisions of molecules with other atoms or collisions of molecules with each other. This study demonstrates that electric fields may be used to enhance or suppress spin-rotation interactions in molecules. The spin-rotation interactions induce nonadiabatic couplings between states of different total spins in systems of two open-shell species and it is suggested that electric fields might be used for controlling nonadiabatic spin transitions and spin-forbidden chemical reactions of cold molecules in a magnetic trap.

Timur V. Tscherbul, Jacek A. Kłos, Łukasz Rajchel +1 more

We present a rigorous study of cold and ultracold collisions of $\mathrm{Yb}\mathrm{F}(^{2}\ensuremath{\Sigma})$ molecules with He atoms in external electric and magnetic fields based on an accurate calculation of the interaction potential surface and quantum theory of atom-molecule scattering. We analyze the mechanisms of collisional depolarization of the electron and nuclear spins of YbF and demonstrate that the rate constants for elastic and inelastic collisions of YbF with He are sensitive to the magnitudes of the applied fields. Collisions of heavy polar molecules like YbF may thus be easily manipulated with external electromagnetic fields. We show that collisional spin relaxation of YbF molecules in rotationally excited states is suppressed by electric fields much more significantly than the spin relaxation in the ground rotational state. We explain this by the influence of electric-field-induced Feshbach resonances, which occur at much lower collision energies when the molecule is rotationally excited. Our results suggest that heavy polar molecules may be amenable to magnetic trapping in a buffer gas of He, which could greatly enhance the sensitivity of spectroscopic experiments to measure the electric dipole moment of the electron.

Břetislav Friedrich

M. Elbs, O. Keck, H. Knöckel +1 more