We present quantum-chemical calculations for the ground and some low-lying excited states of isolated LiCa and LiSr molecules using multi-state complete active space second-order perturbation theory (MS-CASPT2). The potential energy curves (PECs) and their corresponding spectroscopic constants, obtained at the spin-free (SF) and spin-orbit (SO) levels, agree well with available experimental values. Our SO-MS-CASPT2 calculation at the atomic limit (R = 100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% for both LiCa and LiSr. In addition, permanent dipole moments and transition dipole moments at the SF level are also obtained. Rovibrational calculations of the ground and selected excited states, together with the spontaneous emission rates, demonstrate that the formation of ultracold LiCa and LiSr molecules in low-lying vibrational levels of the electronic ground state may be possible.
We present quantum-chemical calculations for the ground and some low-lying excited states of isolated LiCa and LiSr molecules using multi-state complete active space second-order perturbation theory (MS-CASPT2). The potential energy curves (PECs) and their corresponding spectroscopic constants, obtained at the spin-free (SF) and spin-orbit (SO) levels, agree well with available experimental values. Our SO-MS-CASPT2 calculation at the atomic limit (R = 100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% for both LiCa and LiSr. In addition, permanent dipole moments and transition dipole moments at the SF level are also obtained. Rovibrational calculations of the ground and selected excited states, together with the spontaneous emission rates, demonstrate that the formation of ultracold LiCa and LiSr molecules in low-lying vibrational levels of the electronic ground state may be possible.
We report a series of quantum-chemical calculations for the ground and some of the low-lying excited states of an isolated LiYb molecule by the spin-orbit multistate complete active space second-order perturbation theory (SO-MS-CASPT2). Potential energy curves, spectroscopic constants, and transition dipole moments (TDMs) at both spin-free and spin-orbit levels are obtained. Large spin-orbit effects especially in the TDMs of the molecular states dissociating to Yb((3)P(0,1,2)) excited states are found. To ensure the reliability of our calculations, we test five types of incremental basis sets and study their effect on the equilibrium distance and dissociation energy of the ground state. We also compare CASPT2 and CCSD(T) results for the ground state spectroscopic constants at the spin-free relativistic level. The discrepancies between the CASPT2 and CCSD(T) results are only 0.01 Å in equilibrium bond distance (R(e)) and 200 cm(-1) in dissociation energy (D(e)). Our CASPT2 calculation in the supermolecular state (R=100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% error. Transition dipole moments of the super molecular state (R=100 a.u.) dissociating to Li((2)P) excited states are quite close to experimental atomic TDMs as compared to the Yb((3)P) and Yb((1)P) excited states. The information obtained from this work would be useful for ultracold photoassociation experiments on LiYb.
In this work, we present a thorough theoretical structure and spectroscopic study of the ground and low lying excited states of RbBa molecule. High-level ab-initio calculations are performed, using MCSCF/MRCI+Q level of method, based on the effective core potential (ECP) and core-polarization potential (CPP) approach. The potential energy curves, spectroscopic parameters, vibrationnel energy levels of the 16( 2,4 Σ + , 2,4 Π, 2,4 Δ) first electronic states, with respect to the lowest five dissociation limits were calculated. The comparison of the spectroscopic constants of the ground state X 2 Σ + with the available theoretical work, are in good agreement. The study of all the excited states is performed in this work for the first time. Afterwards, the spin-orbit operator is incorporated in valence MRCI calculation using optimized relativistic spin-orbit pseudo-potentials and 33 Ω states are generated and split into Λ-S states. In addition, both relativistic and non relativistic calculations of permanent and transition dipole moments are presented and discussed. Stimulated black body ( T = 300 K) and spontaneous transition rates of vibrational states of X 2 Σ + state were evaluated. The related vibrational lifetimes for RbBa are found to be in order of 10 3 s which is sufficiently large for ultracold experiments. Moreover, the vibrational life-time for the A 2 Σ + ( v’ ) and A 2 П ( v” ) states are measured and the possibility of Laser Cooling for the RbBa molecule is discussed based on Franck–Condon factors calculation of A 2 Σ + ( v’ )→ X 2 Σ + ( v ) and A 2 П( v” ) → X 2 Σ + ( v ) transition. This work represents a significant contribution for experimentalists as it provides efficient information in order to form cold alkali and alkaline-earth RbBa molecules.
We perform a systematic investigation of the electronic properties of the (2)Σ(+) ground state of Li-alkaline-earth dimers. These molecules are proposed as possible candidates for quantum simulation of lattice-spin models. We apply powerful quantum chemistry coupled-cluster method and large basis sets to calculate potential energies and permanent dipole moments for the LiBe, LiMg, LiCa, LiSr, and LiYb molecules. Agreement of calculated molecular constants with existing experimental data is better than or equal to 8%. Our results reveal a surprising irregularity in the dissociation energy and bond length with an increase in the reduced mass of the molecule. At the same time, the permanent dipole moment at the equilibrium separation has the smallest value between 0.01 a.u. and 0.1 a.u. for the heaviest (LiSr and LiYb) molecules and increases to 1.4 a.u. for the lightest (LiBe), where 1 a.u. is one atomic unit of dipole moment. We consider our study of the (2)Σ(+) molecules a first step towards a comprehensive analysis of their interactions in an optical trap.
Ab initio techniques have been applied to investigate the electronic structure of the LiYb molecule. The potential energy curves have been computed in the Born-Oppenheimer approximation for the ground and 29 low-lying doublet and quartet excited electronic states. Complete active space self-consistent field, multi-reference configuration interaction, and Rayleigh Schrödinger perturbation theory to second order calculations have been utilized to investigate these states. The spectroscopic constants, ωe, Re, Be, …, and the static dipole moment, μ, have been investigated by using the two different techniques of calculation with five different types of basis. The eigenvalues, Ev, the rotational constant, Bv, the centrifugal distortion constant, Dv, and the abscissas of the turning points, Rmin and Rmax, have been calculated by using the canonical functions approach. The comparison between the values of the present work, calculated by different techniques, and those available in the literature for several electronic states shows a very good agreement. Twenty-one new electronic states have been studied here for the first time.
In this work, a comprehensive theoretical investigation is carried out to explore the electronic and spectroscopic properties of selected diatomic molecular ions MgRb+ and SrRb+. Using high-level ab initio calculations based on a pseudopotential approach, along with large Gaussian basis sets and full valence configuration interaction (FCI), we accurately determine adiabatic potential energy curves, spectroscopic constants, transition dipole moments (TDMs), and permanent electric dipole moments (PDMs). To deepen our understanding of these systems, we calculate radiative lifetimes for vibrational levels in both ground and low-lying excited electronic states. This includes evaluating spontaneous and stimulated emission rates, as well as the effects of blackbody radiation. We also compute Franck–Condon factors and analyze photoassociation processes for both ions. Furthermore, to explore low-energy collisional dynamics, we investigate elastic scattering in the first excited states (21Σ+) describing the collision between the Ra atom and Mg+ or Sr+ ions. Our findings provide detailed insights into the theoretical electronic structure of these molecular ions, paving the way for future experimental studies in the field of cold and ultracold molecular ion physics.
The adiabatic potential energy curves and the spectroscopic constants of the ground and the first excited states of LiK+, LiRb+ and LiCs+ ionic molecules have been performed. The transition dipole moment between the ground (X2Σ+) and the first excited (22Σ+) state have been determined for each ionic molecule. We have used an ab initio approach involving non‐empirical pseudo‐potentials with core valence effects taken into account through parameterized l‐dependent polarization potentials. Our spectroscopic constants of the ground and the first excited states are in good agreement with the available theoretical works. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the 22Σ+ state for the first time. In addition to the bound‐bound contribution, the bound‐free term has been evaluated exactly and using the Franck‐Condon (FC) approximation and added to the total radiative lifetime. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.