Precision Measurements in Few-Electron Molecules: The Ionization Energy of Metastable ${}^4$He${}_2$ and the First Rotational Interval of ${}^4$He${{}_2}^{+}$

Abstract

Molecular helium represents a benchmark system for testing $\text{ab initio}$ calculations on few-electron molecules. We report on the determination of the adiabatic ionization energy of the $a{}^3{\Sigma }_u^{+}$ state of He${}_2$, corresponding to the energy interval between the $a{}^3{\Sigma }_u^{+}$ ($v^{\prime \prime }=0$, $N^{\prime \prime }=1$) state of He${}_2$ and the $X^{+}{}^2{\Sigma }_u^{+}$ ($v^{+}=0$, $N^{+}=1$) state of He${{}_2}^{+}$, and of the lowest rotational interval of He${{}_2}^{+}$. These measurements rely on the excitation of metastable He${}_2$ molecules to high Rydberg states using frequency-comb-calibrated continuous-wave UV radiation in a counter-propagating-laser-beam setup. The observed Rydberg states were extrapolated to their series limit using multichannel quantum-defect theory. The ionization energy of He${}_2$ ($a{}^3{\Sigma }_u^{+}$) and the lowest rotational interval of He${{}_2}^{+}$ ($X^{+}{}^2{\Sigma }_u^{+}$) are 34301.207002(23)$\pm 0.000037_{\mathrm{sys}}$ cm${}^{-1}$ and 70.937589(23)$\pm 0.000060_{\mathrm{sys}}$ cm${}^{-1}$, respectively.

References in corpus (3)

• Benchmarking theory with an improved measurement of the ionization and dissociation energies of H${}_2$
• QED calculation of the dipole polarizability of helium atom
• High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

Cited by in corpus (1)

• Non-adiabatic, Relativistic, and Leading-order QED Corrections for Rovibrational Intervals of ${}^4$He${}_2^{+}$ ($X{}^2{\Sigma }_{\mathrm{u}}^{+}$)