ИСТИНА

The Quantum Defect Theory (QDT) implementation for ab initio quantum-chemical modeling of highly excited electronic states of atoms and molecules has a long and successful history. The hydrogen dimer (H2) is the first case when the QDT machinery could manage to describe the energy and radiation properties of Rydberg’s diatomic states at the almost spectroscopic level of accuracy. The development of computational capabilities of using the arithmetic of quadruple and even higher accuracy has provided the recent advent of more precise potential energy curves (PECs) for the ground and all excited electronic states of the H2 molecule converging up to fourth dissociation limit [1,2]. In a combination with a highly accurate PEC available for the ground state of molecular cation H2+ [3] it became possible to evaluate, due to the famous Milliken’s equation, the molecular quantum defect functions and their first derivatives with respect to internuclear distances R under the extremely high accuracy and over a very wide range of R. This opens a new opportunities for the detailed description of energetic, radiative and electric properties of highly excited electronic states of H2 istotopomers in the framework of the multi-channel QDT. In this work the single-channel quantum defect functions μlΛ(R), together with dμlΛ/dR, were systematically extracted from ab initio Born-Oppenheimer PECs and their first derivatives with respect to R available for the Rydberg’s states of the H2 molecule [1,2]. A comparative analysis of the asymptotic behavior of the μlΛ(R) functions in the unified He I atom limit and on the dissociation 1s+nl threshold has discovered at small R-values the drop-down points corresponding to the states with large angular moment of Rydberg’s electron l and localized for each state the internuclear distance where configuration interaction and l-mixing effect are both taking place. The adiabatic correction function [4] and non-adiabatic energy shifts were calculated for the particular states under the single-channel QDT approximation and compared with the literature data as well. This work was supported by the Russian Science Foundation (grant No. 23-13-00207, https://rscf.ru/project/23-13-00207/). References: 1. M. Silkowski, M. Zientkiewicz, K. Pachucki, Adv. Quant. Chem. 83, 255–267 (2021). 2. M. Silkowski, K. Pachucki, Mol. Phys. 120 (19-20), e2062471 (2022). 3. D. M. Bishop, R. W. Wetmore, Mol. Phys. 26 (1), 145–157 (1973). 4. K. Dressler, L. Wolniewicz, J. Chem. Phys. 85 (5), 2821–2830 (1986).