Accurate Prediction of the Ammonia Probes of a Variable Proton-to-Electron Mass Ratio

TL;DR

This study uses variational calculations to accurately predict the sensitivity of ammonia molecule transitions to changes in the proton-to-electron mass ratio, highlighting transitions with potential for cosmological measurements.

Contribution

It introduces a robust variational approach to compute sensitivity coefficients of ammonia transitions, emphasizing anomalous sensitivities and isotopic dependencies for probing fundamental constants.

Findings

Certain ammonia transitions show highly anomalous sensitivities to μ variations.

Isotopic differences significantly affect sensitivity coefficients.

The results identify promising ammonia probes for cosmological studies.

Abstract

A comprehensive study of the mass sensitivity of the vibration-rotation-inversion transitions of $^{14}$NH$_3$, $^{15}$NH$_3$, $^{14}$ND$_3$, and $^{15}$ND$_3$ is carried out variationally using the TROVE approach. Variational calculations are robust and accurate, offering a new way to compute sensitivity coefficients. Particular attention is paid to the $\Delta k=\pm 3$ transitions between the accidentally coinciding rotation-inversion energy levels of the $\nu_2=0^+,0^-,1^+$ and $1^-$ states, and the inversion transitions in the $\nu_4=1$ 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 $\mu$. Moreover, a simultaneous comparison of the calculated sensitivities reveals a sizeable isotopic dependence which could aid an exclusive ammonia detection.