Enhanced effects of temporal variation of the fundamental constants in ${}^2{\Pi }_{1/2}$-term diatomic molecules: ${}^{207}$Pb${}^{19}$F

The ${}^{207}$Pb${}^{19}$F molecule possesses a pair of closely spaced levels of opposite parity due to near cancellation of the omega-type doubling and magnetic hyperfine interaction energy shifts [Alphei et al., Phys. Rev. A 83, 040501 (2011)]. We calculate the dependence of the transition frequency between these levels on the fine-structure constant $\alpha$ and the ratio of the light quark masses to the quantum chromodynamics scale $(m_q/{\Lambda }_{\mathrm{QCD}})$, and find large enhancement of the relative effects of the variation of these parameters. Note that the effect of $\alpha$ variation appears mainly due to the significant difference in the relativistic correction factors for the fine and hyperfine structure. We hence suggest the ${}^{207}$Pb${}^{19}$F molecule as a candidate system for investigating the possible temporal variation of the fundamental constants.