Sub-ppb measurement of a fundamental band rovibrational transition in HD

Abstract

We report a direct measurement of the 0-1 R(0) vibrational transition frequency in groundstate 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-per-billion (ppb) uncertainty is limited primarily by the residual first-order Doppler shift.

Lamb-peak spectrum of the HD (2-0) P(1) line

“…For the measurement of the R(2) and R(3) lines no detailed study of the hyperfine structure was performed, but the derived transition frequencies [21] also show an approximate +2σ deviation from the NAPT-results. A similar deviation was found in a recent molecular beam study on HD [41]. It is noted that in all these cases the 2σ offset is given in terms of, and is entirely due to the uncertainty in the theoretical value.…”

Hyperfine components of all rovibrational quadrupole transitions in the H$_{2}$ and D$_{2}$ molecules

“…Theoretical studies of the rovibrational structure of the ground electronic state in molecular hydrogen achieve remarkable accuracy in the determined dissociation energy [1][2][3][4][5] and rovibrational energy levels [6][7][8][9][10][11][12]. The progress in the theoretical investigations is enhanced by recent experiments, which aim at the sub-MHz accuracy of both the dissociation energy [13,14] and the rovibrational transition frequencies in the ground electronic state [15][16][17][18][19][20][21][22][23][24][25][26][27]. Comparison between theoretical calculations and accurate measurements can be used as a test for the quantum electrodynamics for molecules [12], determination of the proton-charge radius [1,8,13,14] or even searches for physics beyond Standard Model [28], i.e.…”