Precision measurement of the rotational energy-level structure of the three-electron molecule He$_2^+$
arXiv:1705.00869 · doi:10.1063/1.4967256
Abstract
The term values of all rotational levels of the $^4$He${_2}^+\,X^+\,^2Σ_u^+\,(ν^+=0)$ ground vibronic state with rotational quantum number $N^+\le 19$ have been determined with an accuracy of 8 x 10$^{-4}$ cm$^{-1}$ ($\sim{25}$ MHz) by MQDT-assisted Rydberg spectroscopy of metastable He$_2^*$. Comparison of these term values with term values recently calculated ab initio by Tung et al. [J. Chem. Phys. 136, 104309 (2012)] reveal discrepancies that rapidly increase with increasing rotational quantum number and reach values of 0.07 cm$^{-1}$ ($\sim{2.1}$ GHz) at $N^+=19$.
11 pages, 6 figures