Frequency metrology on theEFΣg+1←XΣg+1

Abstract

We present a frequency metrology study on the lowest rotational levels of the hydrogen EF 1 ⌺ g + ← X 1 ⌺ g + ͑0,0͒ two-photon transition near 202 nm. For this purpose, the fourth harmonic of an injection-seeded titanium:sapphire pulsed oscillator is employed in a Doppler-free REMPI-detection scheme on a molecular beam of hydrogen. A frequency comb laser is used to perform the absolute frequency calibration on the continuous-wave ͑CW͒ laser that injection-seeds the oscillator. Chirp-induced frequency differences between the output of the pulsed oscillator and the seeding light are monitored on-line, while possible systematic shifts related to the AC-Stark and Doppler effects are addressed in detail. The transition frequencies of the Q͑0͒ to Q͑2͒ lines in H 2 and D 2 , and the Q͑0͒ and Q͑1͒ lines in HD are determined with an absolute accuracy at the 10 −9 level.

Precision spectroscopy of high rotational states in H2investigated by Doppler-free two-photon laser spectroscopy in theEF

“…Doppler shifts, possibly caused by deviations from a perfect alignment of counterpropagating laser beams, are avoided in a Sagnac configuration [34]; residual angular mismatch amounts to some 1 MHz in the calibration uncertainty [21]. The profiles of the observed lines in the Doppler-free geometry are essentially Lorentzian and the observed widths (on average 300 MHz) are determined by the harmonically converted linewidth of the PDA system.…”

“…Results of Bailly et al [28] are included for comparison. a Based on the measurements of Hannemann et al [21]. b Based on the measurements of Salumbides et al [29].…”

“…g system has been amply demonstrated over the years [17][18][19][20][21]. This scheme involving two-photon excitation from the X 1 + g ground state is illustrated in Fig.…”

“…Of relevance for the present study are determinations of level energies up to J = 12 for E(v = 0) and up to J = 5 for E(v = 1-3); it should be noted that the absolute accuracies of level energies in Ref. [28] depend on the determination of anchor lines in the EF state by the two-photon laser experiments [21,29]. Those levels predominantly localized in the inner well Calculations of QED effects in the ground state can also be tested by measuring combination differences, i.e., rotational energy splittings of J = 2 in the X 1 + g ground state from pairs of O(J + 2) and Q(J ), and pairs of Q(J ) and S(J − 2) branch transitions.…”

Spectral identification of diffuse resonances in H2 above the n = 2 dissociation limit

“…21 In a recent experimental study the level energies of many bound quantum states of singlet-g symmetry below the n = 2 dissociation limit were determined at very high precision, 22 with absolute reference to the ground state. 23,24 To assist the discussion the calculated BornOppenheimer potential energy curves of all relevant states of singlet character and gerade symmetry in the region below and above the n = 2 limit [25][26][27] are displayed in Fig. 1.…”