We present a theoretical investigation on the electronic structure and properties of radium monochalcogenides, with chalcogens O, S, and Se, as well as the ionic species RaO +/-. Our approach combines fully relativistic and partially relativistic quantum-chemistry methods. Electronic properties are obtained using the exact two-component Hamiltonian-based coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)+ X2C], while potential energy curves are computed using an internally contracted multireference configuration interaction method, including relativistic effects through small-core pseudopotentials and Pauli-Breit operator diagonalization (MRCI+Q+ECP+SO). The dimers exhibit very large permanent dipole moments and sizable dipolar polarizabilities, while the Franck-Condon factors among the lowest electronic states are highly non-diagonal. These features are discussed in terms of the divalent character of the chemical bonding in the neutral species.
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The paper investigates the electronic structure of radium monochalcogenides RaO, RaS and RaSe, and RaO$^{\pm}$, focusing on bonding, electric-field response and prospects for optical cycling. Potential-energy curves and spectroscopic constants are calculated using multireference configuration interaction with a Davidson correction, relativistic pseudopotentials and spin–orbit state interaction. Permanent dipoles and static polarizabilities are evaluated using finite-field CCSD(T), with both pseudopotential and all-electron exact-two-component treatments; coupled-cluster response calculations provide electronic dispersion coefficients.
The neutral molecules have predominantly divalent bonding and $X^1\Sigma^+$ ground states. Calculated permanent dipoles are approximately $8.9$ D for RaO, $11.2$ D for RaS and $11.5$ D for RaSe, with agreement across the different relativistic treatments. Electronic excitation changes equilibrium bond lengths substantially. Franck–Condon matrices calculated for selected RaO and RaS transitions are non-diagonal, with maximum entries of approximately $0.56$ and $0.61$, respectively, supporting the conclusion that these transitions are unsuitable for laser cooling. Spin-free calculations place the first excited states of RaO$^+$ and RaO$^-$ only $134$ and $217\,\mathrm{cm}^{-1}$ above their ground states.
Accuracy is assessed through coupled-cluster comparisons and benchmarks against RaF, alkaline-earth monofluoride dipoles and BaO spectroscopy. The stated limitations include approximate relativistic and dynamical-correlation treatments, restricted state sets and internuclear grids for spin–orbit calculations, and excitation energies sensitive to methodology. Fully relativistic refinements are left for future work. Suggested dipole-bound anion states and molecular production routes are not investigated directly.
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Central claim may not hold: The explicit Franck–Condon calculations cover only spin-free singlet transitions in RaO and RaS, leaving the broader non-diagonality statement without equivalent direct calculations for the other species or spin–orbit-coupled states.
The reported spin–orbit constants for the RaS X and B states imply a harmonic F00 of approximately 0.93, contradicting the stated rationale that spin–orbit changes are too small to improve vibrational overlap.
The polarizability definition and finite-field formula omit the required minus sign relating physical static polarizability to the second electric-field derivative of the ground-state energy.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
We present a theoretical investigation on the electronic structure and properties of radium monochalcogenides, with chalcogens O, S, and Se, as well as the ionic species RaO +/-. Our approach combines fully relativistic and partially relativistic quantum-chemistry methods. Electronic properties are obtained using the exact two-component Hamiltonian-based coupled-cluster approach with single, double, and perturbative triple excitations [CCSD(T)+ X2C], while potential energy curves are computed using an internally contracted multireference configuration interaction method, including relativistic effects through small-core pseudopotentials and Pauli-Breit operator diagonalization (MRCI+Q+ECP+SO). The dimers exhibit very large permanent dipole moments and sizable dipolar polarizabilities, while the Franck-Condon factors among the lowest electronic states are highly non-diagonal. These features are discussed in terms of the divalent character of the chemical bonding in the neutral species.
The paper investigates the electronic structure of radium monochalcogenides RaO, RaS and RaSe, and RaO±, focusing on bonding, electric-field response and prospects for optical cycling. Potential-energy curves and spectroscopic constants are calculated using multireference configuration interaction with a Davidson correction, relativistic pseudopotentials and spin–orbit state interaction. Permanent dipoles and static polarizabilities are evaluated using finite-field CCSD(T), with both pseudopotential and all-electron exact-two-component treatments; coupled-cluster response calculations provide electronic dispersion coefficients.
The neutral molecules have predominantly divalent bonding and X1Σ+ ground states. Calculated permanent dipoles are approximately 8.9 D for RaO, 11.2 D for RaS and 11.5 D for RaSe, with agreement across the different relativistic treatments. Electronic excitation changes equilibrium bond lengths substantially. Franck–Condon matrices calculated for selected RaO and RaS transitions are non-diagonal, with maximum entries of approximately 0.56 and 0.61, respectively, supporting the conclusion that these transitions are unsuitable for laser cooling. Spin-free calculations place the first excited states of RaO+ and RaO− only 134 and 217cm−1 above their ground states.
Accuracy is assessed through coupled-cluster comparisons and benchmarks against RaF, alkaline-earth monofluoride dipoles and BaO spectroscopy. The stated limitations include approximate relativistic and dynamical-correlation treatments, restricted state sets and internuclear grids for spin–orbit calculations, and excitation energies sensitive to methodology. Fully relativistic refinements are left for future work. Suggested dipole-bound anion states and molecular production routes are not investigated directly.
Abstract Molecular ions formed in cold hybrid ion–atom experiments may find interesting applications ranging from precision measurements to controlled chemical reactions. Here, we investigate the electronic structure of the Sr 2 + molecular ion, which may be produced by photoassociation of laser-cooled Sr+ ions immersed in an ultracold gas of Sr atoms or by ionization of ultracold Sr2 molecules. Using ab initio electronic structure methods, such as the coupled cluster and configuration interaction ones with small-core relativistic energy-consistent pseudopotentials and large Gaussian basis sets, we calculate potential energy curves for the ground and 41 excited electronic states, and electric dipole transition moments between them. We show that alkaline-earth molecular ions, despite their apparently simple structure with only three valence electrons, are challenging for state-of-the-art quantum chemistry methods due to their multireference nature and high density of states. Finally, we calculate and analyze Franck–Condon factors governing the photoionization of ground-state Sr2 molecules into Σ u + 2 and Σ g + 2 states of Sr 2 + molecular ions. The present results may be useful for studying and guiding the formation and spectroscopy of cold Sr 2 + molecular ions.
Abstract Molecular ions formed in cold hybrid ion-atom experiments may find interesting applications ranging from precision measurements to controlled chemical reactions. Here, we investigate electronic structure of the Sr2 + molecular ion, which may be produced by photoassociation of laser-cooled Sr+ ions immersed into an ultracold gas of Sr atoms or by ionization of ultracold Sr2 molecules. Using ab initio electronic structure methods, such as the coupled cluster and configuration interaction ones with small-core relativistic energy-consistent pseudopotentials and large Gaussian basis sets, we calculate potential energy curves for the ground and 41 excited electronic states, and electric dipole transition moments between them. We show that alkaline-earth molecular ions despite of their apparently simple structure with three valence electrons only are challenging for state-of-the-art quantum chemistry methods due to their multireference nature and high density of states. Finally, we calculate and analyze Franck-Condon factors governing the photoionization of ground-state Sr2 molecules into 2Σu + and 2Σg + states of Sr2 + molecular ions. The present results may be useful for studying and guiding formation and spectroscopy of cold Sr2 + molecular ions.
The properties of the electronic ground state of the polar and paramagnetic chromium--closed-shell-atom molecules have been investigated. State-of-the-art ab initio techniques have been applied to compute the potential energy curves for the chromium--alkaline-earth-metal-atom, CrX (X=Be, Mg, Ca, Sr, Ba), and chromium--ytterbium, CrYb, molecules in the Born-Oppenheimer approximation for the high-spin ${X}^{7}{\ensuremath{\Sigma}}^{+}$ electronic ground state. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), was employed and the scalar relativistic effects within the Douglas-Kroll-Hess Hamiltonian or energy-consistent pseudopotentials were included. The permanent electric dipole moments and static electric dipole polarizabilities were computed. The leading long-range coefficients describing the dispersion interaction between the atoms at large interatomic distances C6 are also reported. The molecules under investigation are examples of species possessing both large magnetic and electric dipole moments making them potentially interesting candidates for ultracold many-body physics studies.
The properties of the electronic ground state of the polar and paramagnetic europium--S-state-atom molecules have been investigated. Ab initio techniques have been applied to compute the potential energy curves for the europium--alkali-metal-atom, EuX(X=Li,Na,K,Rb,Cs), europium--alkaline-earth-metal-atom, EuY(Y=Be,Mg,Ca,Sr,Ba), and europium-ytterbium, EuYb, molecules in the Born-Oppenheimer approximation for the high-spin electronic ground state. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), was employed and the scalar relativistic effects within the small-core energy-consistent pseudopotentials were included. The permanent electric dipole moments and static electric dipole polarizabilities were computed. The leading long-range coefficients describing the dispersion interaction between atoms at large internuclear distances C6 are also reported. The EuK, EuRb, and EuCs molecules are examples of species possessing both large electric and magnetic dipole moments making them potentially interesting candidates for ultracold many-body quantum simulations when confined in an optical lattice in combined electric and magnetic fields.
Studies of anions are inherently more challenging than investigations of neutrals and cations because of the diffuse and weakly bound character of an anionic electron. Here, we present a comprehensive computational examination of ground-state diatomic molecular anions composed of alkali-metal (Li, Na, K, Rb, Cs, Fr) and alkaline-earth-metal (Be, Mg, Ca, Sr, Ba, Ra) atoms. We study 21 alkali-metal diatomic anions in the X2Σ+ electronic state and 36 alkali-metal--alkaline-earth-metal diatomic anions in the X1Σ+ electronic state. The calculations employ a hierarchy of the coupled cluster methods, combined with large Gaussian basis sets and small-core relativistic energy-consistent pseudopotentials for heavier elements. We compute potential energy curves, permanent electric dipole moments, and static polarizabilities, and we assess convergence and uncertainties of our results. Additionally, using the multireference configuration interaction and equation-of-motion electron-attachment coupled cluster methods, we investigate excited electronic states of alkali-metal molecular anions, including valence-bound and dipole-bound states. We predict crossings between ground neutral and excited anionic states, which may enhance resonant electron attachment and subsequent anion dissociation. This finding may be relevant for experiments with mixtures of ultracold ground-state alkali-metal molecules and Rydberg atoms.
Ultracold diatomic molecules find application in quantum studies ranging from controlled chemistry and precision measurement physics to quantum many-body simulation and potentially quantum computing. Accurate knowledge of molecular properties is required to guide and explain ongoing experiments. Here, in an extensive and comparative study, we theoretically investigate the electronic properties of the ground-state diatomic molecules composed of alkali-metal (Li, Na, K, Rb, Cs, Fr) and alkaline-earth-metal (Be, Mg, Ca, Sr, Ba, Ra) atoms. We study 78 heteronuclear and homonuclear diatomic combinations, including 21 alkali-metal molecules in the ${X}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ and ${a}^{3}{\mathrm{\ensuremath{\Sigma}}}^{+}$ electronic states, 36 alkali-metal--alkaline-earth-metal molecules in the ${X}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+}$ electronic state, and 21 alkaline-earth-metal molecules in the ${X}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ electronic state. We calculate potential energy curves, permanent electric dipole moments, and polarizabilities using the hierarchy of coupled-cluster methods up to CCSDTQ with large Gaussian basis sets and small-core relativistic energy-consistent pseudopotentials. We collect and analyze corresponding spectroscopic constants. We estimate computational uncertainties and compare the present values with previous experimental and theoretical data to establish a different theoretical benchmark. The presented results should be useful for further application of the studied molecules in modern ultracold physics and chemistry experiments.