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 cancelation 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_{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.
Comment: 6 pages. Includes significant improvement in accuracy of calculations compared with previous versions. Accepted to Physical Review A