Accurate prediction of the ammonia probes of a variable proton-to-electron mass ratio

A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of ¹⁴NH₃, ¹⁵NH₃, ¹⁴ND₃, and ¹⁵ND₃ is carried out variationally using the TROVE approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coeffcients. Particular attention is paid to the Δk=±3 transitions between the accidentally coinciding rotation-inversion energy levels of the ν₂=0⁺, 0⁻ ,1⁺ and 1⁻ states, and the inversion transitions in the v₄ = 1 state affected by the "giant" l-type doubling effect. These transitions exhibit highly anomalous sensitivities, thus appearing as promising probes of a possible cosmological variation of the proton-to-electron mass ratio μ. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection