Sensitivity to a variation of me/mp from splittings between 12C2HD reference frequencies

The sensitivity to a variation of μ of the 2v₁ and v₁+v₃+v₅ bands transitions of ¹²C₂HD in the 193-199 THz spectral domain is calculated with an effective Hamiltonian for the Coriolis interaction between the [200(00)^0e] and [101(01)^1e] energy levels. The frequency splittings between near resonant transitions have sensitivity coefficients to a variation of μ of both signs in the range of 10-10⁵. The degeneracy is due to a cancellation of effective rotational intervals with frequency shifts associated to the vibrational band origins, the anharmonicity and the rotation-vibration interactions. The measurements of a temporal drift of a frequency splitting against the Cs hyperfine frequency may constrain the time variation of μ better than the time variations of α, g_Cs. The systematic frequency shifts are evaluated for intracavity saturated absorption spectroscopy measurements and constrain the measurement of a variation of μ at ~10-10. The comparison between measurements of frequency splittings with sensitivity coefficients of both signs may discriminate a variation of μ at -8×10^-11.