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 (12)

• Non-adiabatic, Relativistic, and Leading-order QED Corrections for Rovibrational Intervals of ${}^4$He${}_2^{+}$ ($X{}^2{\Sigma }_{\mathrm{u}}^{+}$)
• Variational Dirac-Coulomb explicitly correlated computations for atoms and molecules
• From megahertz to terahertz qubits encoded in molecular ions: theoretical analysis of dipole-forbidden spectroscopic transitions in N${}_2^{+}$
• The Bethe-Salpeter QED wave equation for bound-state computations of atoms and molecules
• QED corrections to the correlated relativistic energy: one-photon processes
• Ab initio potential energy curves, scattering lengths, and rovibrational levels of the He${}_2^{+}$ molecular ion in excited electronic states
• One-particle operator representation over two-particle basis sets for relativistic QED computations
• Characterization of the electronic ground state of He${}_2^{+}$ by high-resolution photoelectron spectroscopy
• High-Precision Quantum Dynamics of He${}_2$ over the b ${}^3{\Pi }_{\mathrm{g}}$-c ${}^3{\Sigma }_{\mathrm{g}}^{+}$ Electronic Subspace by including Non-adiabatic, Relativistic and QED Corrections and Couplings
• Precision Spectroscopy of the Fine Structure in the $\mathbf{a}{}^3{\mathbf{\Sigma }}_{\mathbf{u}}^{+}(\mathbf{v}=0)$ and $\mathbf{c}{}^3{\mathbf{\Sigma }}_{\mathbf{g}}^{+}(\mathbf{v}=4)$ States of the Helium Dimer
• Rovibrational computations for He${}_2^{+}$ X ${\Sigma }_{\mathrm{u}}^{+}$ including non-adiabatic, relativistic and QED corrections
• Rovibrational computations for the He${}_2$ a ${}^3{\Sigma }_{\mathrm{u}}^{+}$ state including non-adiabatic, relativistic, and QED corrections