Hyperfine-frequency shifts of alkali-metal atoms during long-range collisions

Collisions with chemically inert atoms or molecules change the hyperfine coupling $A\mathbf{I}·\mathbf{S}$ of an alkali-metal atom through the hyperfine-shift interaction $\delta A\mathbf{I}·\mathbf{S}$. This interaction is responsible for the pressure shifts of the microwave resonances of alkali-metal atoms in buffer gases, is an important spin interaction in alkali-metal–noble-gas van der Waals molecules, and is anticipated to enable the magnetoassociation of ultracold molecules such as RbSr. An improved estimate is presented for the long-range asymptote of this interaction for Na, K, Rb, and Cs. To test the results, the change in hyperfine coupling due to a static electric field is estimated and reasonable agreement is found.