Anomalous phosphine sensitivity coefficients as probes for a possible variation of the proton-to-electron mass ratio

TL;DR

This study uses a variational approach to examine how phosphine's rotation-vibration spectrum responds to potential variations in the proton-to-electron mass ratio, revealing anomalous sensitivities due to molecular interactions that could be useful in astrophysical tests.

Contribution

It uncovers anomalous sensitivity coefficients in phosphine caused by Coriolis interactions and degeneracies, suggesting new probes for fundamental constant variation in space.

Findings

Anomalous sensitivity coefficients identified in phosphine spectra.

Enhanced sensitivities due to Coriolis interactions and degeneracies.

Potential for detecting proton-electron mass ratio variations in astrophysical environments.

Abstract

A robust variational approach is used to investigate the sensitivity of the rotation-vibration spectrum of phosphine (PH$_3$) to a possible cosmological variation of the proton-to-electron mass ratio, $\mu$. Whilst the majority of computed sensitivity coefficients, $T$, involving the low-lying vibrational states acquire the expected values of $T\approx-1$ and $T\approx-1/2$ for rotational and ro-vibrational transitions, respectively, anomalous sensitivities are uncovered for the $A_1\!-\!A_2$ splittings in the $\nu_2/\nu_4$, $\nu_1/\nu_3$ and $2\nu_4^{\ell=0}/2\nu_4^{\ell=2}$ manifolds of PH$_3$. A pronounced Coriolis interaction between these states in conjunction with accidentally degenerate $A_1$ and $A_2$ energy levels produces a series of enhanced sensitivity coefficients. Phosphine is expected to occur in a number of different astrophysical environments and has potential for investigating a drifting constant. Furthermore, the displayed behaviour hints at a wider trend in molecules of ${\bf C}_{3\mathrm{v}}\mathrm{(M)}$ symmetry, thus demonstrating that the splittings induced by higher-order ro-vibrational interactions are well suited for probing $\mu$ in other symmetric top molecules in space, since these low-frequency transitions can be straightforwardly detected by radio telescopes.