Anomalous phosphine sensitivity coefficients as probes for a possible variation of the proton-to-electron mass ratio
Abstract
A robust variational approach is used to investigate the sensitivity of the rotation-vibration spectrum of phosphine (PH3) to a possible cosmological variation of the proton-to-electron mass ratio, mu. Whilst the majority of computed sensitivity coefficients, T, involving the lowlying vibrational states acquire the expected values of T approximate to -1 and T approximate to -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(l= 0)(4)/2 nu(l=2)(4) manifolds of PH3.
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 C-3v(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.