Range Of Internuclear Distances Research Articles

Molecular line lists for the singlet states in gaseous YN at high temperature

ABSTRACT Our aim in this study is to investigate the electronic structure of the gaseous YN molecule and provide an accurate molecular line list of spectroscopic transitions between the five lowest singlet states. The calculations were done by using large basis set for yttrium aug-cc-pVQZ-PP with relativistic effective core potentials at the spin-free level. We first used the method of complete active space self-consistent field, which was followed by the multireference singles and doubles configuration interaction. Potential energy curves and permanent and transition dipole moments were calculated at the internuclear distance range of 1.3–2.96 Å. For each state, we calculated the spectroscopic constants (Te, ωe, ωexe, ωeye, Be, αe, Re). The calculated values of the spectroscopic constants are in excellent agreement with the experimental constants available, with a relative difference of less than 5 cm−1. We further calculated the transition intensities of allowed transitions, and we provided the absorption spectra up to a temperature of 4000 K. The computed molecular line list contains 2.6 million transitions calculated between almost 18 186 vibro-rotational energy levels. It covers the frequency range between 0 and 30 000 cm−1. The effect of temperature on the spectra of hot YN was investigated with partition functions calculated between 298 and 4000 K. This study should help in identifying the singlet state spectrum of the hot YN molecule, which is possibly found in the atmospheres of cool stars and hot rocky super-Earths.

UNDULATING POTENTIALS OF RYDBERG Σ+-STATES OF ME-RG MOLECULES: NON-EMPIRICAL TREATMENT OF NA-HE EXCIPLEX

The multi-reference con guration interaction method based on single and double excitations (MR-CISD), l-independent core polarization potential (CPP) and diffuse function-saturated cc-pVQZ and aug-cc-pV5Z basis sets for Na and He atoms, respectively, have been used to perform non-relativistic calculations of potential energy curves and permanent dipole moment functions for the ground and excited electronic states of the exciplex Na-He molecule up to the Na(62S) state. The ab initio results obtained in a wide range of internuclear distances R [1.7, 20.0] (Å) have quantitatively claimed the undulating behavior of interatomic potentials, predicted within the framework of the inelastic scattering theory. It has been established that at large R the interatomic potentials and dipole moments of highly excited (3,6,10)2Σ+ states, converging to Na (n = 4, 5, 62S)+He(22S) atomic limits, are modulated by the nodal structure of the radial Rydberg wave function (n > 3) s-electron of Na atom during its scattering on the remote He atom.

Ab Initio Potential Energy Surface for NaCl-H2 with Correct Long-Range Behavior.

We report a full dimensional ab initio potential energy surface for NaCl-H2 based on precise fitting of a large data set of CCSD(T)/aug-cc-pVTZ energies. A major goal of this fit is to describe the very long-range interaction accurately. This is done in this instance via the dipole-quadrupole interaction. The NaCl dipole and the H2 quadrupole are available through previous works over a large range of internuclear distances. We use these to obtain exact effect charges on each atom. Diffusion Monte Carlo calculations are done for the ground vibrational state using the new potential.

HCl, DCl and TCl diatomic molecules in their ground state: predicting Born–Oppenheimer rovibrational spectra

The analytic Born–Oppenheimer (B-O) potential curve for the ground state of the molecule (H,D,T)Cl is constructed for the whole range of internuclear distances with an accuracy of 3–5 significant figures in comparison with the Rydberg–Klein–Rees-style potential curve derived from available experimental data on vibrational energies. With an accuracy of 3–4 significant figures, energy predictions are made for HCl (DCl, TCl) for the 836 (1625, 2366) B-O rovibrational bound states with maximal vibrational number and maximal angular momentum , including 24 (46, 63) weakly-bound states (close to the dissociation limit) with energies Hartree. The insufficiency of existing experimental data is indicated, and predictions for the bulk of the missing rovibrational states are made for all HCl, DCl, and TCl molecules.

Extrapolation properties of the Morse-Long Range potential at large internuclear distances

The accuracy of the potential energy curves for diatomic molecules determined from experimental data is confirmed empirically with numerous examples in the literature. Usually PECs are determined from a limited set of experimental data and this in turns limits the range of internuclear distances where the shape of the potential is unambiguously fixed. While the uncertainty for interpolation could be assessed, the extrapolation is usually questionable and needs careful analyses. The Morse/Long-Range potential (Le Roy and Henderson, 2007) has been reported to have a built in long-range asymptotic behavior and therefore it is plausible to expect that one can expect good extrapolation properties and even possibility to determine important molecular parameters like De or/and Cm from limited set of experimental data. In this contribution we undertake a systematic study which confirms these expectations in the case of Ca2 ground state.

Ab-initio study of the electronic structure of LaF including spin-orbit coupling.

Spectroscopic investigation of lanthanum monofluoride molecule LaF is carried out by ab-initio methods and all the observed band systems are predicted through the fine structure of LaH. This structure consisted of 67 Ω(±) states is calculated by taking into account the spin-orbit coupling effect of lanthanum. Therefore, these Ω(±) states are degenerated from 33 low-lying 1,3Λ(±) states below 33,200cm-1. The potential energy curves (PECs) of 1,3Λ(±) and Ω(±) states are displayed in the range of internuclear distance from 1.40 to 3.00Å and their spectroscopic constants ([Formula: see text],[Formula: see text], [Formula: see text], [Formula: see text]) are reported. Moreover, the permanent and the transition dipole moments are plotted as a function of internuclear distance. Furthermore, the composition of the Ω(±) state-wave functions in terms of Λ-S parent states is calculated at the equilibrium internuclear distance of the ground state. Furthermore, through calculating the splitting energy between the spin-orbit components of a 3Λ(±) state, Hund's case of many states involved in the observed band systems is determined.

ClF diatomic molecule: Rovibrational spectra

Following the first principles the analytic Born–Oppenheimer (BO) potential curve for the ground state X1Σ+ of the molecule ClF is proposed for whole range of internuclear distances R∈[0,∞). It is based on matching the perturbation theory at small internuclear distances R and multipole expansion at large distances R, it has the form of two-point Pade approximant and provides 3–4 figures in rovibrational energies. It supports 5719 rovibrational states with maximal vibrational number νmax=47 and maximal angular momentum Lmax=210 including 36 weakly-bound states close to threshold (to dissociation limit) with the energies ≲10-4hartree. The van der Waals constant C6(ClF)∼29.3a.u. is predicted.

Competing ionization and dissociation in the H$$_{2}$$ gerade system

A numerically solvable two-dimensional (2D) model, employed by the authors to study the dissociative recombination of H$_2^+$ in the ungerade symmetry [Phys. Rev. A $\mathbf{98}$, 062706 (2018)], is extended to describe the collision process in the gerade symmetry of H$_2$. In this symmetry the ionization and dissociation processes are driven primarily by the direct, curve-crossing mechanism. The model is represented by a set of three coupled electronic channels in 2D, in the space of $s,p,d$ partial waves of the colliding electron. We demonstrate that the Born-Oppenheimer properties of the H$_2$ molecule in the relevant range of internuclear distances can be described by such a model. The molecular rotational degrees of freedom are accounted for by the rotational frame transformation. The numerical solution of the model is discussed and the resulting rovibrationally inelastic and dissociative recombination cross sections are compared with the available data.

One-Electron Energy Spectra of Heavy Highly Charged Quasimolecules: Finite-Basis-Set Approach

The generalized dual-kinetic-balance approach for axially symmetric systems is employed to solve the two-center Dirac problem. The spectra of one-electron homonuclear quasimolecules are calculated and compared with the previous calculations. The analysis of the monopole approximation with two different choices of the origin is performed. Special attention is paid to the lead and xenon dimers, Pb82+–Pb82+–e− and Xe54+–Xe54+–e−, where the energies of the ground and several excited σ-states are presented in the wide range of internuclear distances. The developed method provides the quasicomplete finite basis set and allows for the construction of perturbation theory, including within the bound-state QED.

New insight into the spectroscopy of LaH by ab-initio methods

By ab-initio methods, the spectroscopy of lanthanum hydride molecule LaH is predicted and the states involved in all the observed band systems are assigned. So, 34 low - lying 1,3Λ(±) states located below 31400 cm−1 are calculated and 67 Ω(±) states are generated by taking into account the spin–orbit coupling effect of lanthanum. For these states, the spectroscopic constants such as Re, Te, ωe and ωeχe are determined and the potential energy curves (PECs) are plotted in the range of internuclear distance from 1.00 Å to 3.00 Å. The calculated electronic configuration of 1,3Λ(±) states shows the ionic nature La+H- of this species. Moreover, the composition of the Ω(±) state-wave functions in term of Λ-S parent states are calculated at the equilibrium internuclear distance of the ground state. Indeed, this molecule belongs to Hund’s case (c) since the transition in many observed band systems only obeys the rule ΔΩ = 0, ±1.

Accurate semiempirical potential energy curves for the a3Σ+-state of NaCs, KCs, and RbCs.

A five parameter semiempirical Tang-Toennies type model is used to describe the potential curves of the a3Σ+-state of the heteronuclear polar molecules NaCs, KCs, and RbCs. These molecules are of current interest in experiments at ultra-cold conditions to explore the effects of the strong dipole-dipole forces on the collective many-body quantum behavior. New quantum phenomena are also anticipated in systems consisting of atomic species with different fermion/boson statistics. The model parameters are obtained by simultaneously fitting all five of the parameters to the extensive LIF-Fourier transform spectroscopy published by Tiemann and collaborators [e.g., Docenko et al. J. Phys. B: At., Mol. Opt. Phys. 39, S929-S943 (2006)], who also report best fit potential curves. Although the new potentials are in good agreement with the earlier potentials, they have the advantage that they are continuous over the entire range of internuclear distances and have the correct long-range behavior. The scattering lengths for all isotope combinations show good agreement with dedicated experiments where available. The new potentials are also in excellent agreement with combining rules based on the potentials of the homonuclear systems.

Ab initio investigation of ground and excited states of ScH molecule

The theoretical study of the electronic structure of Scandium Hydride ScH has been carried out using ab-initio methods. By employing (MRCI-SD/SA-CASSCF) and by using basis sets involving contribution of all electrons of both Scandium and Hydrogen atoms, 18 singlet and 15 triplet low-lying electronic states have been calculated below 28803 cm−1. Potential energy curves have been plotted and the term values at equilibrium Te, the vibrational constants ωe and ωeχe of ScH electronic states have been fitted. In addition, we calculated the permanent electric dipole moments for all these predicted states, the transition dipole moments TDMs within states at a range of internuclear distance around the equilibrium, the vibronic intensities FCF and the radiative lifetime. The calculated spectroscopic constants are in excellent consistency with the available experimental results and with other previous theoretical works. These calculations also predicted many excited states unobserved experimentally. The observed perturbations in D1Π and C1Σ+ have been investigated in this work.

Conformal Analytical Potential for All the Rare Gas Dimers over the Full Range of Internuclear Distances

An analytical model for the potential between two rare gas atoms at distances between R=0 to R→∞ is assumed to be conformal with the previously published potential for He_{2} [J. Chem. Phys. 142, 131102 (2015)JCPSA60021-960610.1063/1.4916740]. The potential curves of the rare gas dimers all have the same shape and only depend on the well parameters D_{e} and R_{e}. The potentials and the vibrational levels for the 11 homonuclear and heteronuclear dimers for which recent abinitio calculations are available agree, within several percent, with the abinitio results. For the other rare gas dimers, the new potential provides the first realistic estimates for the potentials.

Theoretical study of MgNa+ ionic system: potential energy curve, vibrational levels, dipole moments, radiative lifetimes and laser-cooling analysis

An extensive ab-initio quantum chemistry study and a discussion of the possible laser cooling and formation of the heteronuclear ionic MgNa+ molecule is presented in this paper. Our work is based on the use of non–empirical pseudo-potentials for the Mg2+ and Na+ cores, large Gaussian basis sets, parametrized l–dependent polarization potentials, and full valence configuration interaction calculations. We present here adiabatic potential energy curves of the ground and 44 low-lying excited electronic states of 1,3Σ+, 1,3Π, 1,3Δ symmetries, and their spectroscopic parameters (Re, De, Te, ωe, ωexe, and Be). Furthermore, numerous ionic – neutral avoided crossings, specially between higher adjacent electronic states of 1,3Σ+, 1,3Π symmetries, are identified and interpreted. The energy separations between these avoided crossings are also calculated. The electric dipole moment curves have been computed for a wide range of inter-nuclear distances. The vibrational energies are obtained by solving the nuclear Schrodinger equation, using the calculated potential energy curves. Thereafter, spontaneous and black-body radiation induced transition rates are calculated to obtain the ground and excited states vibrational level lifetimes. It has been observed that the lifetimes of the ground state vibrational levels are of the order of a second, while those of the excited states, mainly the 21Σ+ state, have the order of a nanosecond.

Long-range Rydberg molecule Rb2 : Two-electron R -matrix calculations at intermediate internuclear distances

The adiabatic potential energy curves of Rb$_2$ in the long-range Rydberg electronic states are calculated using the two-electron \textit{R}-matrix method [M. Tarana, R. \v{C}ur\'{i}k, Phys. Rev. A \textbf{93}, 012515 (2016)] for the intermediate internuclear separations between 35 a.u. and 200 a.u. The results are compared with the zero-range models to find a region of the internuclear distances where the Fermi's pseudopotential approach provides accurate energies. A finite-range potential model of the atomic perturber is used to calculate the wave functions of the Rydberg electron and their features specific for the studied range of internuclear distances are identified.

An accurate semiempirical potential energy curve for the a3Σ+-state of KRb.

A semiempirical potential energy curve for the a3Σ+-state of the KRb molecule with only five parameters is reported. The potential is continuous over the entire range of internuclear distances and has the correct long-range attractive dispersion potential from established theory. The potential provides an equally good fit of the laser induced fluorescence Fourier transform spectroscopic data of Pashov et al. [Phys. Rev. A 76, 022511 (2007)] as their multi-parameter potential. The new potential is supported by the good agreement of the well parameters De, Re and the harmonic vibrational constant ωe with combining-rule estimates. The scattering lengths for all six isotopologues are also in excellent agreement with experiment with a 0.2% adjustment within theoretical uncertainty of the leading dispersion coefficient C6. An analysis of the harmonic vibrational constant ωe and the constant ωexe of the potential of Pashov et al. reveals a significant difference to the present potential which turned out to be due to an oscillatory deviation in their potential in the vicinity of the potential minimum. The new potential is, thus, the best available because its simplicity is ideal for further applications.

Ab initio study of R-dependent behavior of the hyperfine structure parameters for the [formula omitted] states of LiRb and LiCs

Diagonal a3Σ1+-a3Σ1+ and off–diagonal X1Σ0++-a3Σ0-+ magnetic hyperfine structure (HFS) matrix elements were calculated ab initio for the LiRb and LiCs molecules in a wide range of internuclear distances using the multi–reference Fock space coupled clusters method with generalized relativistic effective core potentials to describe the four–component valence wavefunctions near the nuclei. At large distances, both HFS functions vary little, though they may fluctuate by as much as 12 to 24% in the intermediate range. The plateau exhibited by the a3Σ1+-a3Σ1+ HFS function at 4–5 Å, could be attributed to pronounced spin–orbit coupling of the intersecting a3Σ+ and b3Π states.

A basis-set error correction based on density-functional theory for strongly correlated molecular systems

We extend to strongly correlated molecular systems the recently introduced basis-set incompleteness correction based on density-functional theory (DFT) [E. Giner et al., J. Chem. Phys. 149, 194301 (2018)]. This basis-set correction relies on a mapping between wave-function calculations in a finite basis set and range-separated DFT (RSDFT) through the definition of an effective non-divergent interaction corresponding to the electron-electron Coulomb interaction projected in the finite basis set. This enables the use of RSDFT-type complementary density functionals to recover the dominant part of the short-range correlation effects missing in this finite basis set. To study both weak and strong correlation regimes, we consider the potential energy curves of the H10, N2, O2, and F2 molecules up to the dissociation limit, and we explore various approximations of complementary functionals fulfilling two key properties: spin-multiplet degeneracy (i.e., independence of the energy with respect to the spin projection Sz) and size consistency. Specifically, we investigate the dependence of the functional on different types of on-top pair densities and spin polarizations. The key result of this study is that the explicit dependence on the on-top pair density allows one to completely remove the dependence on any form of spin polarization without any significant loss of accuracy. Quantitatively, we show that the basis-set correction reaches chemical accuracy on atomization energies with triple-ζ quality basis sets for most of the systems studied here. In addition, the present basis-set incompleteness correction provides smooth potential energy curves along the whole range of internuclear distances.

The collision cross-sections for proton–argon interaction based on ab initio potential

The classical collision cross-sections of a proton with an argon atom as well as the thermal transport coefficients and rate constant of the colliding $\text{H}^{+}-\text{Ar}$ system are evaluated at the kinetic temperature $T\in [100,10\,000]~(\text{K})$ by means of the asymptotically correct analytical potential constructed for the ground $X^{1}\unicode[STIX]{x1D6F4}^{+}$ state of the ArH+ cation from the highly accurate ab initio data available in the entire range of internuclear distances (Terashkevich et al., J. Quant. Spectrosc. Radiat. Transfer, vol. 234, 2019, pp. 139–146). The results can be useful to estimate thermodynamic, transport and kinetic properties of the Ar/H2 plasma in a wide temperature range.

Theoretical study of the electronic structure of mono-bromide of lanthanum molecule including spin-orbit coupling effects.

Among the family of lanthanide halides compounds, this work is devoted to the third halogen bromine. The presented lanthanum bromide LaBr molecule has a remarkable scientific interest regarding the other molecules because it presents few experimental studies and only one theoretical study. The theoretical electronic structure of the LaBr molecule is achieved by using the post-Hartree-Fock methods manifested by the complete active space self consistent field (CAS-SCF) method and the multi reference configuration interaction with single and double excitation (MRCI-SD) method. All of these calculations are performed via the quantum chemistry software MOLPRO. We predicted for the first time in the literature, 24 lowest-lying electronic states in the representation 2S+ 1Λ(±) and their corresponding components in the representation Ω(±) when taking into account the spin-orbit coupling (SOC), situated below 22,000 cm- 1. We calculated the spectroscopic constants for both cases (without/with SOC effects) related to the 13 singlet and 11 triplet states and for their components. We drew also in this paper the potential energy curves (PECs in a range of internuclear distance R varying from 2.00 to 4.22 Å. Graphical AbstractPotential energy curves for 13 singlet electronic states of LaBr.