Electronic structure of the polar molecules XF (X: Be, Mg, Ca) with rovibrational and dipole moment calculations

Production of ultracold polyatomic molecules with strong polarity by laser cooling: A detailed theoretical study on CaNC and SrNC

Laser cooling molecules to the ultracold regime is the prerequisite for many novel science and technologies. It is desirable to take advantage of theoretical approaches to explore polyatomic molecular candidates, which are capable of being cooled to the ultracold regime. In this work, we explore two polyatomic candidates, CaNC and SrNC, which are suitable for laser cooling. These molecules possess impressively large permanent dipole moments (∼6 Debye), which is preferred for applications using an external electric field. High-level ab initio calculations are carried out to reveal electronic structures of these molecules, and the calculated spectroscopic constants agree very well with the available experimental data. For each molecule, the Franck-Condon factor matrix is calculated and shows a diagonal distribution. The radiative lifetimes for CaNC and SrNC are estimated to be 15.5 and 15.8 ns, respectively. Based upon the features of various electronic states and by choosing suitable spin-orbit states, we construct two feasible laser cooling schemes for the two molecules, each of which allows scattering nearly 10000 photons for direct laser cooling. These indicate that CaNC and SrNC are excellent ultracold polyatomic candidates with strong polarity.

High resolution laser excitation spectra and Franck-Condon factors of A2Π−X2Σ+ electronic transition of MgF

Magnesium monofluoride (MgF) is proposed as an ideal candidate radical for direct laser cooling. Here, the rotationally resolved laser spectra of MgF for the A2Π− X2Σ+ electronic transition system were recorded by using laser induced fluorescence technique. The MgF radicals were produced by discharging SF6/Ar gas mixtures between the tips of two magnesium needles in a supersonic jet expansion. We recorded a total of 19 vibrational bands belonging to three sequences of Δ v=0, ±1 in the region of 348-370 nm. Accurate spectroscopic constants for both X2Σ+ and A2Π states are determined from rotational analysis of the experimental spectra. Spectroscopic parameters, including the Franck-Condon factors (FCFs), are determined from the experimental results and the Rydberg-Klein-Rees (RKR) calculations. Significant discrepancies between the experimentally measured and RKR-calculated FCFs are found, indicating that the FCFs are nearly independent of the spin-orbit coupling in the A2Π state. Potential energy curves (PECs) and FCFs determined here provide necessary data for the theoretical simulation of the laser-cooling scheme of MgF.

Multireference study of ionic/covalent electronic states of MF (M = Be, Mg and Ca)

Ultracold environments composed by atoms or molecules offer an opportunity to study chemical reactions at the quantum-state level, for simulation of solid-state systems, as qubits in quantum computing, and for test fundamental symmetries. Those ultracold conditions formed by molecules can be obtained from cryogenic buffer gas, via supersonic expansion, followed by deceleration or from the laser cooling process. Diatomic alkaline earth monofluoride molecules have been shown as great candidates for the laser cooling process. In this sense, the present work focuses on the characterization of the low-lying doublet electronic states correlated to the first dissociation channel of the alkaline earth monofluorides diatomic molecules MF (M = Be, Mg and Ca). The developed state-of-the-art methodology was based on a qualitative analysis of the diatomic electronic structure, employing a hypothetical potential energy curve or by a simple molecular orbital diagram combined with bond order analysis. The potential energy curves, excitation and dissociation energies, and various sets of spectroscopic parameters were calculated by the MRCI/cc-pV5Z methodology. Transition probabilities for emission and radiative lifetimes among the characterized electronic states were also calculated for the (A)²Π ⟶ (X)²Σ⁺ electronic transition. Comparing the spectroscopy properties, we were able to indicate the CaF molecule as the best candidate molecule for laser cooling devices among the studied molecules.

Electronic Structure with Rovibrational Calculations of the Magnesium Monohalides MgX and Their Cations MgX+ (X = Cl, Br, and I)

Alkaline-earth monohalides are popular compounds that are used in various applications. Little is known, however, in terms of electronic structure, about their cations and their low-lying electronic states. We present in this work electronic structure ab-initio calculations based on multireference configuration interaction plus Davidson correction of three magnesium monohalides and their cations (MgCl, MgBr, MgI, MgCl⁺, MgBr⁺, and MgI⁺). We determine the spectroscopic constants T _e, R _e, ω_e, B _e, and α_e and the dissociation energies D _e for their bound states. Additionally, we investigate their vibrational properties by calculating the vibrational eigenvalue E _v, the rotational constant B _v, and the centrifugal distortion constant D _v. We additionally study the electric charge distribution of several states by determining their permanent dipole moment and transition dipole moment curves. Finally, we calculate the Franck-Condon factors and the radiative lifetimes as precursors for laser cooling experiments.

Electronic Structure with Dipole Moment and Rovibrational Calculation of Cadmium Chalcogenide Molecules CdX (X = Se, Te)

Ab initio calculations of 51 electronic states in the representation 2s+1Λ(±) of CdX (X = Se, Te) molecules have been carried out by using the complete active space self-consistent field and multireference configuration interaction (single and double excitations with the Davidson correction). The potential energy along with the static and transition dipole moment curves for the investigated electronic states of the CdX molecules has been mapped. Consequently, the spectroscopic constants R e, ωe, B e, and T e have been computed for the bound states. The spectroscopic dissociation energy D e, the zero-point energy, and the ionicity are also calculated for the bound electronic states X3Π, (1)1Σ+, (1)1Π, and (1)3Σ+. Rovibrational calculation is performed for the X3Π, (1)1Σ+, (1)1Π, and (1)3Σ+ states of CdSe together with the X3Π, (1)1Σ+, and (1)1Π states of a CdTe molecule. The Einstein coefficients of spontaneous and induced emissions, A 21 and B 21, are computed for the transition between the electronic states (1)3Σ+ and X3Π. In the present work, the values are well-consistent with those available in the literature.

The hyperfine structure branching ratios and ab initio study on low-lying electronic states for 24Mg19F molecule

The potential energy curves (PECs) of the fourteen low-lying Λ-S electronic states, spectroscopic constants, transition properties for the ²⁴Mg¹⁹F molecule are calculated at the multi-reference configuration interaction level of theory. The spin-orbit coupling effects are also taken into account in the electronic structure calculations. Spectroscopic constants agree well with previously obtained theoretical and experimental values. Based on the potential energy curves and transition dipole moments, the highly diagonally distributed Franck-Condon factors (f₀₀ = 0.975, f₁₁ = 0.926) for the A²Π (v' = 0, 1) → X²Σ⁺ (v″ = 0, 1) transition are determined. Moreover, it is important to note that the dissociation energy (2.68 eV) of the B²Σ⁺ state is achieved for the first time. Then, employing a quantum effective Hamiltonian approach, we investigate the hyperfine structure branching ratios between the A²Π_1/2 state and the X²Σ_1/2⁺ state. And the numerically analyze is obtained for a simple one-dimension (1D) case on ²⁴Mg¹⁹F molecular MOT. We hope that these data can provide a helpful reference for the assignment and analysis of guiding further experimental spectroscopic measurements and laser cooling in experimental on the ²⁴Mg¹⁹F molecule.

Solution of the Rovibrational Schrödinger Equation of a Molecule Using the Volterra Integral Equation

By using the Rayleigh-Schrödinger perturbation theory the rovibrational wave function is expanded in terms of the series of functions ϕ0,ϕ1,ϕ2,…ϕn, where ϕ0 is the pure vibrational wave function and ϕι are the rotational harmonics. By replacing the Schrödinger differential equation by the Volterra integral equation the two canonical functions α0 and β0 are well defined for a given potential function. These functions allow the determination of (i) the values of the functions ϕι at any points; (ii) the eigenvalues of the eigenvalue equations of the functions ϕ0,ϕ1,ϕ2,…ϕn which are, respectively, the vibrational energy Ev, the rotational constant Bv, and the large order centrifugal distortion constants Dv,Hv,Lv….. Based on these canonical functions and in the Born-Oppenheimer approximation these constants can be obtained with accurate estimates for the low and high excited electronic state and for any values of the vibrational and rotational quantum numbers v and J even near dissociation. As application, the calculations have been done for the potential energy curves: Morse, Lenard Jones, Reidberg-Klein-Rees (RKR), ab initio, Simon-Parr-Finlin, Kratzer, and Dunhum with a variable step for the empirical potentials. A program is available for these calculations free of charge with the corresponding author.