Year: 2022
Type: article
Abstract: This work discusses a protocol for constructing highly accurate potential energy curves (PECs) for the lowest two states of ${\mathrm{Rb}}_{2}^{+}$, i.e., $X\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{g}^{+}$ and $(1)\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$, using an additivity scheme based on coupled-cluster theory. The approach exploits the findings of our previous work [J. Schnabel, L. Cheng, and A. K\"ohn, J. Chem. Phys. 155, 124101 (2021)] to avoid the unphysical repulsive long-range barrier occurring for symmetric molecular ions when perturbative estimates of higher-order cluster operators are employed. Furthermore, care was taken to reproduce the physically correct exchange splitting of the $X\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{g}^{+}$ and $(1)\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ PECs. The accuracy of our computational approach is benchmarked for ionization energies of $\mathrm{Rb}$ and for spectroscopic constants as well as vibrational levels of the $a\phantom{\rule{0.16em}{0ex}}{}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ triplet state of ${\mathrm{Rb}}_{2}$ . We study high-level correlation contributions, high-level relativistic effects, and inner-shell correlation contributions and find very good agreement with experimental reference values for the atomic ionization potential and the binding energy of ${\mathrm{Rb}}_{2}$ in the $a\phantom{\rule{0.16em}{0ex}}{}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ triplet state. Our final best estimate for the binding energy of the ${\mathrm{Rb}}_{2}^{+} X\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{g}^{+}$ state including zero-point vibrational contributions is ${D}_{0}=6179\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ with an estimated error bound of $O(\ifmmode\pm\else\textpm\fi{}30\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$. This value is smaller than the experimentally inferred lower bond of ${D}_{0}\ensuremath{\ge}6307.5\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ [M. A. Bellos et al., Phys. Rev. A 87, 012508 (2013)] and will require further investigation. For the $(1)\phantom{\rule{0.16em}{0ex}}{}^{2}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ state a shallow potential with ${D}_{0}=78.4\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and an error bound of $\ifmmode\pm\else\textpm\fi{}9\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ is computed.
Source: Physical Review A
Authors: Jan Schnabel, Lan Cheng, Andreas Köhn
Language: Latvian
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4295865238