SCIENTIFIC PUBLICATION: Precision Measurements in Few-Electron Molecules: The Ionization Energy of Metastable 4He2 and the First Rotational Interval of 4He2+

Precision Measurements in Few-Electron Molecules: The Ionization Energy of Metastable 4He2 and the First Rotational Interval of 4He2+

L. Semeria, P. Jansen, G.-M. Camenisch, F. Mellini, H. Schmutz, & F. Merkt

Molecular helium represents a benchmark system for testing ab initio calculations on few-electron molecules. We report on the determination of the adiabatic ionization energy of the a 3Σu+ state of He2, corresponding to the energy interval between the a 3Σu+ (v′′=0, N′′=1) state of He2 and the X+2Σu+ (v+=0, N+=1) state of He2+, and of the lowest rotational interval of He2+. These measurements rely on the excitation of metastable He2 molecules to high Rydberg states using frequency-comb-calibrated continuous-wave UV radiation in a counterpropagating laser-beam setup. The observed Rydberg states were extrapolated to their series limit using multichannel quantum-defect theory. The ionization energy of He2 (a 3Σu+) and the lowest rotational interval of He2+ (X+2Σu+) are 34 301.207 002(23)±0.000 037syst cm−1 and 70.937 589(23)±0.000 060syst cm−1, respectively.

Full article:

Phys. Rev. Lett. Vol. 124, p. 213001 (2020)

doi: 10.1103/PhysRevLett.124.213001