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Second-order effects on the hyperfine structure of $P$ states of alkali-metal atoms

We analyze second-order $M1$-$M1$ and $M1$-$E2$ effects to the hyperfine structure (HFS) of the lowest energy $P$ states of alkali-metal atoms arising from the coupling of the two ($J=1/2,3/2$) fine-structure levels through the hyperfine interaction. We find these effects to be especially sizable in Li, leading to a $9σ$ correction to the most accurate reported experimental value of the $A(P_{1/2})$ HFS constant of $^7$Li [D. Das and V. Natarajan, J. Phys. B \textbf{41}, 035001 (2008)]. For the remaining alkali-metal systems, the results tabulated within may be referenced as higher precision is sought in experimental determination of the HFS constants.