44 research outputs found

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

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    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 14NH3. 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 14NH3 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

    Accurate prediction of H<sub>3</sub>O<sup>+</sup> and D<sub>3</sub>O<sup>+</sup> sensitivity coefficients to probe a variable proton-to-electron mass ratio

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    The mass sensitivity of the vibration–rotation–inversion transitions of H316O+, H318O+, and D316O+ is investigated variationally using the nuclear motion program TROVE (Yurchenko, Thiel & Jensen). The calculations utilize new high-level ab initio potential energy and dipole moment surfaces. Along with the mass dependence, frequency data and Einstein A coefficients are computed for all transitions probed. Particular attention is paid to the Δ|k| = 3 and Δ|k − l| = 3 transitions comprising the accidentally coinciding |J, K = 0, v2 = 0+〉 and |J, K = 3, v2 = 0−〉 rotation–inversion energy levels. The newly computed probes exhibit sensitivities comparable to their ammonia and methanol counterparts, thus demonstrating their potential for testing the cosmological stability of the proton-to-electron mass ratio. The theoretical TROVE results are in close agreement with sensitivities obtained using the non-rigid and rigid inverter approximate models, confirming that the ab initio theory used in the present study is adequate

    Analysis of NMR spectra by differentiation with respect to a parameter

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

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    A robust variational approach is used to investigate the sensitivity of the rotation-vibration spectrum of phosphine (PH3_3) to a possible cosmological variation of the proton-to-electron mass ratio, μ\mu. Whilst the majority of computed sensitivity coefficients, TT, involving the low-lying vibrational states acquire the expected values of T1T\approx-1 and T1/2T\approx-1/2 for rotational and ro-vibrational transitions, respectively, anomalous sensitivities are uncovered for the A1 ⁣ ⁣A2A_1\!-\!A_2 splittings in the ν2/ν4\nu_2/\nu_4, ν1/ν3\nu_1/\nu_3 and 2ν4=0/2ν4=22\nu_4^{\ell=0}/2\nu_4^{\ell=2} manifolds of PH3_3. A pronounced Coriolis interaction between these states in conjunction with accidentally degenerate A1A_1 and A2A_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 C3v(M){\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 μ\mu in other symmetric top molecules in space, since these low-frequency transitions can be straightforwardly detected by radio telescopes

    Vibrational linestrengths for the ground and first excited electronic states of HeH2 +

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    Studies in the pyridine series. XIII. NMR-shift ranges for some isomeric alkylsubstituted tetrahydropyridines

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    Radiative association of He+2: the role of quartet states

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