Fundamental vibration frequency and rotational structure of the first excited vibrational level of the molecular helium ion (He2+)

Abstract

The term values of rotational levels of the first excited vibrational state of the electronic ground state of He2 + with rotational quantum number N + ≤ 13 have been determined with an accuracy of 1.2 × 10 −3 cm −1 (∼35 MHz) by MQDT-assisted Rydberg spectroscopy of metastable He2. Comparison of the experimental term values with the most accurate ab initio results for He2 + available in the literature [W.-C. Tung, M. Pavanello, and L. Adamowicz, J. Chem. Phys. 136, 104309 (2012)] reveals inconsistencies between theoretical and experimental results that increase with increasing rotational quantum number. The fundamental vibrational wavenumber of He2 + was determined to be 1628.3832(12) cm −1 by fitting effective molecular constants to the obtained term values.

Nonadiabatic, Relativistic, and Leading-Order QED Corrections for Rovibrational Intervals of He42+ ( Ferenc1, Korobov2, Mátyus3 2020Phys. Rev. Lett.

“…By including also the leading-order QED corrections in the theoretical treatment both the fundamental vibration energy, the rotational and the rovibrational excitation energies come in agreement with experiment with a root-mean-squared deviation (RMSD) of 0.001 7 and 0.001 9 cm −1 , respectively. The experimental uncertainty of the rotational and rovibrational series is slightly smaller than these values [12,13], they are 0.000 8 and 0.0001 2 cm −1 , respectively. The lowest-energy rotational interval, (0, 3)-(0, 1), has been recently measured more precisely, 70.937 589(23) ± 0.000 06 sys [9], and our theoretical value for this interval is 70.937 69(10) cm −1 .…”

“…Precise knowledge of this quantity is necessary for a possible new definition of the pressure standard based on counting the number density of a sample of helium gas. There has been experimental progress in the precision spectroscopy of 4 He + 2 including the measurement of the spin-rotational fine structure [10] and the rotational and rovibrational intervals [9,[11][12][13].…”

“…For the derivation of the error estimates to the computed energies see Table I. [13] 1628.3832 (12) 1627.9318 (12) 1696.6096(12) ν expt −ν calc 0.0023 0.0027 0.0019 [13] 1997.5633 (12) 2512.6871 (12) 2848.3690(12) ν expt −ν calc 0.0029 0.0004 0.0012…”

“…Deviation of the rotational and (ro)vibrational excitation energies of the 4 He + 2 molecular ion (X 2 Σ + u ) from experiment[9,12,13]. (v, N + ) labels the vth vibrational state with the N + rotational quantum number.…”

Non-adiabatic mass-correction functions and rovibrational states of 4He2+ (X 2Σu+)

“…After submission of this work, we became aware of new measurements which determine rotational intervals for the first vibrational excitation (v = 1) and the vibrational fundamental frequency of 4 He + 2 [48]. The increasing experimental dataset will allow a more detailed study of the fine interplay of small effects earlier neglected in the theoretical description of this molecular ion.…”