Sensitivity to proton-to-electron mass ratio variation from pairs of isotopic lithium hydride rotational and rovibrational transitions

Abstract

Calculations of the sensitivities of rotational and rovibrational transitions of isotopic lithium hydride in the electronic ground state to a variation of the proton-to-electron mass ratio constant are presented. A highly enhanced sensitivity coefficient is observed for the splitting of near resonant transitions arising from a cancellation between rotational intervals and frequency shifts associated respectively to the isotope effect, to the anharmonicity and to the rotation-vibration interaction. It ranges from 73 748.47(1) to −21 672(137) for the transitions with low to intermediate rotational quantum numbers in the lowest vibrational energy levels. The splittings of rotational transitions of 7LiD in the vibrational level v = 0 and 6LiD in the vibrational level v = 2 have a sensitivity coefficient of ∼−3 for J up to 29 and that of 6LiH R(0) and 7LiH R(1) rovibrational transitions in the v = 0 − >1 band has a sensitivity coefficient of −585. The approach allowed comparison of frequency intervals between rotational lines with ammonia inversion lines detected in the microwave spectra of B0218 + 367 quasar to put constraints to a variation of the proton-to-electron mass ratio.