Enhanced sensitivity to a possible variation of the proton-to-electron mass ratio in ammonia

Numerous accidental near degeneracies exist between the 2ν2 and ν4 rotation-vibration energy levels of ammonia. Transitions between these two states possess significantly enhanced sensitivity to a possible variation of the proton-to-electron mass ratio μ. Using a robust variational approach to determine the mass sensitivity of the energy levels along with accurate experimental values for the energies, sensitivity coefficients have been calculated for over 350 microwave, submillimeter, and far-infrared transitions up to J=15 for NH314. The sensitivities are the largest found in ammonia to date. One particular transition, although extremely weak, has a sensitivity of T=-16738 and illustrates the huge enhancement that can occur between close-lying energy levels. More promising however are a set of previously measured transitions with T=-32 to 28. Given the astrophysical importance of ammonia, the sensitivities presented here confirm that NH314 can be used exclusively to constrain a spatial or temporal variation of μ. Thus certain systematic errors which affect the ammonia method can be eliminated. For all transitions analyzed we provide frequency data and Einstein A coefficients to guide future laboratory and astronomical observations