Molecular Spectroscopic Constants Research Articles

Molecular study of an improved Wei energy potential for the halogens and gallium halides

An improved Wei potential energy function as a molecular potential model has not been widely reported probably due to its physical structure. In this study, the Feinberg–Horodecki (FH) equation is examined for the improved Wei energy potential function. To validate the calculations, the Feinberg–Horodecki equation is transformed into an energy equation by putting c=1, and Pn=En. Numerical results are generated for some molecules using the energy equation and the molecular spectroscopic constants for λ=-0.1,0, and 0.1. The predicted results for the energy eigenvalues are compared with the experimental data for four halogen molecules and four gallium halides. The results revealed that the negative values of λ do not produce values that align with the experimental data. It is also shown that the result obtained with λ=0 reproduces a better result for the improved Wei potential energy function than the result obtained with λ=0.1.

Diatomic molecular energy spectra and thermodynamic properties of exponential inversely quadratic plus improved deformed exponential-type potential

By employing the Pekeris-type approximation to deal with the centrifugal term, we study the thermodynamic properties and approximate analytical solutions of the Schrödinger equation with the exponential inversely quadratic plus improved deformed exponential-type potential using parametric Nikiforov–Uvarov method and hypergeometric functional analysis method. The complex eigen energy equation was presented in a closed and compact form and extended to study partition function and other thermodynamic properties. The total normalized wave functions were also obtained and expressed in terms of hypergeometric Jacobi polynomial. The mathematical accuracy of analytical calculation can be verified consistently by comparing numerical data and results of different arbitrarily l state. The potential also reduces to improved deformed exponential-type potential as a special case. We calculated energy spectra for some selected diatomic molecules namely: Silicon Flouride (SiF+ (X1∑+), Oxygen molecule O2+ (X2∏g), Nitrogen molecule, N2+ (X1∑g+), Sulphur chloride SCl and Rubidium hydride RbH using standard molecular spectroscopic constants as applied to the two methods. The results show that the energy eigenvalues for these selected diatomic molecules are in excellent agreement using the two methods and also increases with an increase in quantum state.

Quantum computations in heavy noble-gas hydride cations: Reference energies and new spectroscopic data

Computational quantum chemistry has become a powerful tool with a wide range of possibilities to solve chemical-physical problems. As a result of this, the interest in the applications of computational quantum chemistry has expanded considerably, and has opened up novel research opportunities. In particular, those related to the characterization of heavy-atoms complexes, as most electronic structure calculations for such systems struggle with the problem posed by the large number of electrons present in them, and consequently, the introduction of relativistic effects. The present study performed an exhaustive assess to characterized the uncommon NgH+ (Ng = Kr, Xe, and Rn) hydride cations in order to provide accurate rovibrational data of their isotopes to assist in the laboratory characterization or even their astronomical detection. Scalar relativistic effects were included, and the ground and first electronically exited states potential curves were obtained from benchmark ab initio CCSD(T)/CBS and MRCI+Q electronic structure calculations. Next, such interaction potentials, correctly extended to long-range asymptotic regions, were employed in quantum bound state calculations and molecular spectroscopic constants were determined for the most abundance 84Kr, 132Xe, and 222Rn isotopes. Our results were discussed in comparison with available experimental and previous theoretical estimates, aiming to treat accuracy issues. The new sets provide reference data that could serve for spectroscopic characterization of such low abundance and high radioactive species.

A computational study of the low-lying electronic states of diatomic beryllium bismuthide

We have performed high-level ab initio computations to provide information associated with potential energy curves, molecular structures, electronic structures and vibrational energy levels of BeBi, which is yet an experimentally unknown species. Spectroscopic constants for twelve Λ-S states of the first four Λ-S dissociation channels are obtained for the first time. The feature of seven low-lying excited Ω states of BeBi, corresponding to the first three Ω dissociation limits, has been reported. The spin-orbit coupling effect is proved to have caused a significant impact on the investigated electronic states and interactions among them. Moreover, transition probabilities, such as transition dipole moments, Franck-Condon factors, Einstein coefficients, vibrational branching ratios and radiative lifetimes, are calculated for selected transition bands. Accompany computations are also been carried out for other Be-VA group diatomics of BeN, BeP and BeAs. Relevant data correlated with BeSb are collected from our previous study [Spectrochim. Acta A 208 (2019) 124]. Regular tendencies associated with molecular structures and spectroscopic constants are demonstrated from BeN to BeBi. We expect this work will extend our knowledge of the Be-VA group species and satisfy demands for experimental detections on BeBi.

A simple model for high rotational excitations of molecules in a superfluid

Recently it became possible to study highly excited rotational states of molecules in superfluid helium through nonadiabatic alignment experiments (Cherepanov et al 2021 Phys. Rev. A 104 L061303). This calls for theoretical approaches that go beyond explaining renormalized values of molecular spectroscopic constants, which suffices when only the lowest few rotational states are involved. As the first step in this direction, here we present a basic quantum mechanical model describing highly excited rotational states of molecules in superfluid helium nanodroplets. We show that a linear molecule immersed in a superfluid can be seen as an effective symmetric top, similar to the rotational structure of radicals, such as OH or NO, but with the angular momentum of the superfluid playing the role of the electronic angular momentum in free molecules. The simple theory sheds light onto what happens when the rotational angular momentum of the molecule increases beyond the lowest excited states accessible by infrared spectroscopy. In addition, the model allows to estimate the effective rotational and centrifugal distortion constants for a broad range of species and to explain the crossover between light and heavy molecules in superfluid 4He in terms of the many-body wavefunction structure. Some of the above mentioned insights can be acquired by analyzing a simple 2 × 2 matrix.

Computational Characterization of Astrophysical Species: The Case of Noble Gas Hydride Cations.

Theoretical–computational studies together with recent astronomical observations have shown that under extreme conditions in the interstellar medium (ISM), complexes of noble gases may be formed. Such observations have generated a wide range of possibilities. In order to identify new species containing such atoms, the present study gathers spectroscopic data for noble gas hydride cations, NgH+ (Ng = He, Ne, Ar) from high-level ab initio quantum chemistry computations, aiming to contribute in understanding the chemical bonding and electron sharing in these systems. The interaction potentials are obtained from CCSD(T)/CBS and MRCI+Q calculations using large basis sets, and then employed to compute vibrational levels and molecular spectroscopic constants for all known stable isotopologues of ground state NgH+ cations. Comparisons with previously reported values available are discussed, indicating that the present data could serve as a benchmark for future studies on these systems and on higher-order cationic noble gas hydrides of astrophysical interest.

Theoretical investigation on the low-lying electronic states of diatomic magnesium bismuthide including the spin-orbit coupling effect

High-level ab initio computations have been performed to investigate molecular structures, potential energy curves, vibrational energy levels and spectroscopic constants for twelve Λ-S states of the first four dissociation limits of MgBi. Characterizations of seven Ω states, corresponding to the first and the second Λ-S dissociation limits, have been explored for the first time. The spin–orbit coupling effect is revealed to have introduced a significant impact on the pattern of these electronic states and interactions among them. Our predictions for molecular structures and spectroscopic constants of MgBi are compared with available data of other magnesium-group 18 family species. Regular tendencies of these parameters are clearly exhibited when the group 18 atom is replaced by another one in the group. Information associated with transition dipole moments, Franck-Condon factors, vibrational branching ratios and radiative lifetimes between the Ω states are obtained and their transitional properties are analyzed and discussed. The results and data determined in this work are expected to guide and assist laboratorial detections of MgBi and to extend our understanding for the magnesium-group 18 species.

Spectroscopic properties and cold elastic collisions of alkaline-earth Mg + Mg+ system

In this theoretical work, we calculate molecular potential energy curves, spectroscopic constants and transition dipole moments for the ground and first excited electronic states (A2Πu) of alkaline-earth molecular ion We consider an ab initio multi-reference configuration interaction method using an aug-cc-pv5z Gaussian basis set and compare our results with those obtained by others. The comparison shows a very good agreement. In addition, we investigate the ion-atom elastic collisions for a wide range of energies including the isotopic effect. In close connections, we determine the scattering T-matrix elements for ground-state electronic potentials, which show divergent behavior at a particular energy, indicating the occurrence of scattering resonances. We find that the s-wave scattering length is positive for both ground-state potentials. We also study possible free-bound transitions and Franck–Condon overlap for our system.

Theoretical study of the low-lying adiabatic states of the NaLi+ molecular ion

With one active electron, the NaLi+ cation is a relatively simple system to study, and a good candidate for which results issue from different approaches can be compared to cross check the reliability of different theoretical methods for the calculation of the adiabatic potential energies. However, comparison of the ab initio results of Berriche (2003) and those of Magnier and Frécon (2001), employing model potential methods, is showing a serious disagreement concerning several molecular states. In particular, the low-lying states 22Σ+,42Σ+,62Σ+,82Σ+,102Σ+ and 42Π obtained by Magnier and Frécon, are found to be repulsive whereas they are attractive when ab initio methods are used.To clarify the origin of such a disagreement, in this work, the NaLi+ cation is re-investigated within the framework of the model potential approach. Adiabatic energies and corresponding molecular spectroscopic constants of states dissociating up to the limit Li++Na(4d) are computed. A good agreement with the previous ab initio calculations is observed.

Theoretical study of the electronic structure of mono-chloride of lanthanum molecule including spin-orbit coupling effect.

Our investigation is devoted to the theoretical study of the low-lying electronic structure of the LaCl molecule by using ab initio quantum methods. We are concerned with several methods such as the complete active space-self consistent field (CAS-SCF) and the multi reference of configuration interaction (MRCI + Q) methods. These methods are applied for the purpose of drawing the potential energy curves (PECs) and calculating the molecular spectroscopic constants for a given number of electronic states of singlet and triplet multiplicity. We count 26 2S+ 1 Λ(±) electronic states located below 24,000 cm- 1 neglecting the spin-orbit effects and 47 Ω(±) components taken into consideration these effects. Our calculations are performed via the quantum ab initio package MOLPRO (Werner and Knowles 2000). Graphical Abstract A new set of low-lying electronic states on the theoretical energetic level diagram for the LaCl molecule among the first four lanthanum monhalides.

Potential energy curves of the Na2+ molecular ion from all-electron ab initio relativistic calculations

ABSTRACTThe equation-of-motion coupled-cluster method for electron affinity calculations has been used to study potential energy curves (PECs) for the Na+2 molecular ion. Although the studied molecule represents the open shell system the applied approach employs the closed shell Na+ 22 ion as the reference. In addition the Na+ 22 system dissociates into the closed shell fragments; hence, the restricted Hartree–Fock scheme can be used within the whole range of interatomic distances, from 2 to 45 Å. We used large basis set engaging 268 basis functions with all 21 electrons correlated. The relativistic effects are included via second-order Douglas–Kroll method. The computed PECs, spectroscopic molecular constants and vibrational energy levels agree well with experimental values if the latter are available or with other theoretical data.

A revised study of the [formula omitted] alkali-dimer using a model potential approach

The model potential approach is well adapted to study atomic and molecular systems involving a single active electron. Such is the case of the alkali-dimer lithium cation Li2+. However, a comparison of the model potential results of Magnier et al. (1999) and those based on ab initio techniques (Bouzouita et al., 2006; Jasik et al., 2007, Musial et al., 2015) raises a number of questions related to the existence of an important disagreement regarding several excited states,which are found to be repulsive by Magnier et al. (1999) but attractive when ab initio techniques are employed.In this paper, we propose to re-investigate the Li2+ system, using a model potential technique to compute the adiabatic energy curves and the molecular spectroscopic constants. Our aim is to clarify whether this disagreement between the ab initio and model potential methods originates from some conceptual defect of the model potential technique or whether there is some source of error in the calculations of Magnier et al. (1999).

Theoretical study of LiCl− and LiBr− molecular ions

The molecular structures and spectroscopic constants of the ground electronic states of LiCl− and LiBr− are investigated with the coupled-cluster method. To improve the accuracy of our calculations, we have employed the extrapolation schemes as well as corrections of the core–valence correlation and scalar relativistic effect. The equilibrium parameters, potential energy curves, force constants, vibrational energy levels and spectroscopic parameters of both molecular ions are derived, in which those of LiBr− are reported for the first time. The electron affinities and vertical detachment energies of neutral and anionic LiCl and LiBr are also evaluated.

Action spectroscopy of SrCl⁺ using an integrated ion trap time-of-flight mass spectrometer.

The photodissociation cross-section of SrCl(+) is measured in the spectral range of 36,000-46,000 cm(-1) using a modular time-of-flight mass spectrometer (TOF-MS). By irradiating a sample of trapped SrCl(+) molecular ions with a pulsed dye laser, X(1)Σ(+) state molecular ions are electronically excited to the repulsive wall of the A(1)Π state, resulting in dissociation. Using the TOF-MS, the product fragments are detected and the photodissociation cross-section is determined for a broad range of photon energies. Detailed ab initio calculations of the SrCl(+) molecular potentials and spectroscopic constants are also performed and are found to be in good agreement with experiment. The spectroscopic constants for SrCl(+) are also compared to those of another alkaline earth halogen, BaCl(+), in order to highlight structural differences between the two molecular ions. This work represents the first spectroscopy and ab initio calculations of SrCl(+).

Structural, Spectroscopic and Vibrational Properties for Low-Lying Electronic States of LiCl

A multireference configuration interaction (MRCI) study has been carried out on the LiCl molecule. The potential energy has been calculated over a wide range of internuclear separation for the 21 low-lying electronic states of the LiCl molecule dissociating into Li (2S, 2P, 3S)+Cl (2P). The (4)1Σ+, (3)1Π, 1–33Σ+, 1–33Π, 1,3Δ, 1,3Σ−, (5)1Σ+, (4)3Σ+, (4)1Π, (4)3Π excited states are studied for the first time in theory. Molecular spectroscopic constants (Re,De, ωe, ωeχe, Be and αe) have been derived for the 9 bound states (X1Σ+, (3)1Σ+, (2)3Σ+, 1,3Δ, 1,3Σ−, (4)1Π, (4)3Π) with a regular shape, and the spectroscopic constants of ground states X1Σ+ are in good agreement with available experimental and theoretical values. The relative differences between experimental values and our values for Re, De,ωe, ωeχe, Be and αe are 1.02%, 0.60%, 1.72%, 9.46%, 2.0%, and 0.75%, respectively. Moreover, vibrational levels of 9 bound states, which have not been investigated experimentally, are computed.

Gaussian basis sets of quadruple zeta quality for potassium through xenon: application in CCSD(T) atomic and molecular property calculations

All-electron segmented contracted quadruple zeta valence plus polarization function (QZP) basis sets for the elements from K to Xe were constructed to be used in conjunction with the non-relativistic and Douglas–Kroll–Hess (DKH) Hamiltonians. The QZP-DKH set is obtained from the original QZP basis set, that is, the values of the contraction coefficients were re-optimized using the relativistic DKH Hamiltonian. This extends earlier works on segmented contracted QZ basis set for atoms H–Ar. At the coupled-cluster level of theory, the convergence of atomic ionization energy as well as of molecular spectroscopic constants as a function of basis set size is examined. Additional improvements on spectroscopic constants were achieved by applying corrections due to core–valence correlation and spin–orbit effects. This leads to estimates for the spectroscopic constants of various diatomics in gaseous phase. One verifies that the experimental and benchmark theoretical bond lengths, atomization energies, and harmonic vibrational frequencies can be reproduced well with the QZP-DKH set.

Structure and interactions of ultracold Yb ions and Rb atoms

In order to study ultracold charge-transfer processes in hybrid atom-ion traps, we have mapped out the potential-energy curves and molecular parameters for several low-lying states of the Rb, Yb${}^{+}$ system. We employ both a multireference configuration interaction and a full configuration interaction (FCI) approach. Turning points, crossing points, potential minima, and spectroscopic molecular constants are obtained for the lowest five molecular states. Long-range parameters, including the dispersion coefficients, are estimated from our ab initio data. The separated-atom ionization potentials and atomic polarizability of the ytterbium atom (${\ensuremath{\alpha}}_{d}=128.4$ atomic units) are in good agreement with experiment and previous calculations. We present some dynamical calculations for (adiabatic) scattering lengths for the two lowest (Yb, Rb${}^{+}$) channels that were carried out in our work. However, we find that the pseudopotential approximation is rather limited in validity and only applies to nK temperatures. The adiabatic scattering lengths for both the triplet and singlet channels indicate that both are large and negative in the FCI approximation.

One‐electron pseudopotential study of the alkali hydride cation NaH+: Structure, spectroscopy, transition dipole moments, and radiative lifetimes

AbstractThe structure and spectroscopic properties of the ground and the lowest excited electronic states of the alkali hydride cation NaH+ have been investigated using an ab initio approach. In this approach, a nonempirical pseudopotential for the Na+ core has been used and a core–core and a core‐valence correlation corrections have been added. The adiabatic potential energy curves and the molecular spectroscopic constants for numerous electronic states of 2Σ+, 2Π, and 2Δ symmetries, dissociating up to Na (4d) + H+ and Na+ + H (3d), have been calculated. As no experimental data are available, we discuss our results by comparing with the available theoretical calculations. A satisfying agreement has been found for the ground state with previous works. However, a clear disagreement between this study and the model potential work of Magnier (Magnier, J. Phys. Chem. A 2005, 109, 5411) has been observed for several excited states. Numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries have been found and analysed. They are related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Na+H and NaH+. Furthermore, we provide an extensive set of data concerning the transition dipole moments from X2Σ+ and the 22Σ+ states to higher excited states of 2Σ+ and 2Π symmetries. Finally, the adiabatic potential energy curves of the ground (X2Σ+) and the first (22Σ+) excited states and the transition dipole moments between these states are used to evaluate the radiative lifetimes for the vibrational levels of the 22∑+ state for the first time. In addition to the bound–bound contribution, the bound‐free term has been evaluated and added to the total radiative lifetime. © 2012 Wiley Periodicals, Inc.

Molecular-ion trap-depletion spectroscopy of BaCl+

We demonstrate a simple technique for molecular ion spectroscopy. BaCl$^+$ molecular ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground X$^1\Sigma^+$ state to the repulsive wall of the A$^1\Pi$ state. The photodissociation spectrum is recorded by monitoring the induced trap loss of BaCl$^+$ ions as a function of excitation wavelength. Accurate molecular potentials and spectroscopic constants are determined. Comparison of the theoretical photodissociation cross-sections with the measurement shows excellent agreement. This study represents the first spectroscopic data for BaCl$^+$ and an important step towards the production of ultracold ground-state molecular ions.

Crystal field theory analysis of rovibrational spectra of carbon monoxide monomers isolated in solid parahydrogen

We report the first rotationally resolved and completely assigned rovibrational spectrum for a nonhydride molecule rotating in the solid phase: carbon monoxide (CO) monomers isolated in cryogenic solid parahydrogen (p-H(2)). We employ a modified crystal field theory model, in which the CO molecular spectroscopic constants are taken as adjustable parameters, to make good spectroscopic assignments for all the observed features. We discuss the limitations of this approach and highlight the need for improved theoretical models of molecular rotation dynamics in quantum solids.