Probing me/mp variation by comparison of near-resonant acetylene reference lines at 1.5 ?m

Laboratoire PhLAM, CNRS UMR 8523, Villeneuve d´Ascq, France Frequency comparison of two near-resonant rovibrational transitions f1,2 in the electronic ground state is discussed to probe variation of electron-to-proton mass ratio μ. Sensitivities to fractional variation of μ for acetylene reference rovibrational transitions at 1.5 μm are calculated from the Dunham expansion of molecular energy levels. Frequency difference between near-resonant transitions has an enhanced sensitivity. Pairs of transitions from 12C2H2, 13C2H2, 12C2HD isotopic species with an enhancement of ~103 are identified. Low systematic frequency shift uncertainties of clocks based on acetylene saturated absorption lines make this approach promising for search of small variation of μ.