Sub-ppb Measurement of a Fundamental Band Rovibrational Transition in HD

Abstract

We report a direct measurement of the 1-0 Rð0Þ vibrational transition frequency in ground-state hydrogen deuteride (HD) using infrared-ultraviolet double resonance spectroscopy in a molecular beam. Ground-state molecules are vibrationally excited using a frequency comb referenced continuous-wave infrared laser, and the excited molecules are detected via state-selective ionization with a pulsed ultraviolet laser. We determine an absolute transition frequency of 111 448 815 477(13) kHz. The 0.12 parts-perbillion (ppb) uncertainty is limited primarily by the residual first-order Doppler shift.

Rotational level spacings in HD from vibrational saturation spectroscopy

“…The uncertainties associated with the observed line shape remain to be a dominating factor and hinder full exploitation of the extreme resolution of the saturation technique, and the determination of transition frequencies at the highest accuracy. The molecular-beam double-resonance study of the R(0) line of the (1-0) fundamental of HD by Fast and Meek [20] does not suffer from this shortcoming, yielding a vibrational splitting in HD at the level of 13 kHz, the most accurate to date. Vibrational splittings in the (1-0) fundamental have also been determined via laser-precision studies in molecular beams and the measurement of combination differences in Doppler-free electronic spectra [21].…”

Stimulated Raman scattering metrology of molecular hydrogen

“…The excitation was fostered by a strong static electric field that induces a transition dipole moment in the molecule and thus enhances the absorption of an intense comb-referenced mid-infrared laser. The overall setup remains quite complex and challenging to scale to purely rotational transitions, that would require far-infrared lasers 20 .…”

The (2–0) R(0) and R(1) transition frequencies of HD determined to a 10−10 relative accuracy by Doppler spectroscopy at 80 K

“…21 and changing the sign of some of them as mentioned in ref. 18. Other spectroscopic parameters were obtained from a global fit including experimental data concerning the ν = 0 11,41 and ν = 2 12,17,25 states.…”

“…Indeed, the full width at half maximum (FWHM) of the Doppler limited profile of the (2–0) R (0) or R (1) HD lines is about 700 MHz at 80 K. Saturation spectroscopy provides a powerful tool to circumvent Doppler broadening. Recently, accurate measurements of HD transitions were reported in the sub-Doppler regime using either action spectroscopy schemes 18,24 or the power enhancement of a Fabry Perot cavity to observe Doppler free Lamb dip signatures. 15,25 In particular, the Hefei 15 and Amsterdam 25 groups retrieved the (2–0) R (1) transition frequencies from Lamb dips exhibiting a dispersive-like spectral structure.…”