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arXiv · 1608.08976

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

J. Biesheuvel·J. -Ph. Karr·L. Hilico·K. S. E. Eikema·W. Ubachs·J. C. J. Koelemeij
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Abstract

Recently we reported a high precision optical frequency measurement of the (v,L):(0,2)->(8,3) vibrational overtone transition in trapped deuterated molecular hydrogen (HD+) ions at 10 mK temperature. Achieving a resolution of 0.85 parts-per-billion (p.p.b.) we found the experimental value ($ν_0= 383,407,177.38(41)$ MHz) to be in agreement with the value from molecular theory ($ν_\text{th}=383,407,177.150(15)$ MHz) within 0.6(1.1) p.p.b. [Biesheuvel et al., Nat. Commun. 7, 10385 (2016)]. This enabled an improved test of molecular theory (including QED), new constraints on the size of possible effects due to 'new physics', and the first determination of the proton-electron mass ratio from a molecule. Here, we provide the details of the experimental procedure, spectral analysis, and the assessment of systematic frequency shifts. Our analysis focuses in particular on deviations of the HD+ velocity distribution from thermal (Gaussian) distributions under the influence of collisions with fast ions produced during (laser-induced) chemical reactions, as such deviations turn out to significantly shift the hyperfine-less vibrational frequency as inferred from the saturated and Doppler-broadened spectrum, which contains partly unresolved hyperfine structure.

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J. Biesheuvel, J. -Ph. Karr, L. Hilico, K. S. E. Eikema, W. Ubachs, J. C. J. Koelemeij. 2016-08-31. High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level. https://doi.org/10.1007/s00340-016-6576-8

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