Low-lying Doublet Electronic States Research Articles

Analysis of measured high-resolution doublet rovibronic spectra and related line lists of 12CH and 16OH.

Detailed understanding of the energy-level structure of the quantum states as well as of the rovibronic spectra of the ethylidyne (CH) and the hydroxyl (OH) radicals is mandatory for a multitude of modelling efforts within multiple chemical, combustion, astrophysical, and atmospheric environments. Accurate empirical rovibronic energy levels, with associated uncertainties, are reported for the low-lying doublet electronic states of 12CH and 16OH, using the Measured Active Rotational-Vibrational Energy Levels (Marvel) algorithm. For 12CH, a total of 1521 empirical energy levels are determined in the primary spectroscopic network (SN) of the radical, corresponding to the following seven electronic states: X 2Π, A 2Δ, B 2Σ−, C2 Σ+, D 2Π, E 2Σ+, and F 2Σ+. The energy levels are derived from 6348 experimentally measured and validated transitions, collected from 29 sources. For 16OH, the lowest four doublet electronic states, X 2Π, A 2Σ+, B 2Σ+, and C 2Σ+, are considered, and a careful analysis and validation of 15 938 rovibronic transitions, collected from 45 sources, results in 1624 empirical rovibronic energy levels. The large set of spectroscopic data presented should facilitate the refinement of line lists for the 12CH and 16OH radicals. For both molecules hyperfine-resolved experimental transitions have also been considered, forming SNs independent from the primary SNs.

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.

The suitability of barium monofluoride for laser cooling from ab initio study

ABSTRACTThe feasibility of laser cooling the 138Ba19F molecule is performed using ab initio quantum chemistry. Three low-lying doublet electronic states X 2Σ+, A' 2Δ and A 2Π are determined by the multireference configuration-interaction (MRCI) method, where the spin–orbit coupling (SOC) effect is also taken into account in the electronic structure calculations. The computed spectroscopic constants and permanent dipole moments agree well with the available experimental data. The Franck–Condon factors of the A 2П → X 2Σ+ transition show highly diagonal dominance (f00 = 0.981, f11 = 0.940, f22 = 0.896) and the A 2П state has a radiative lifetime of τ = 37.8 ns, allowing for rapid laser cooling. Our calculation indicates that the laser-cooling scheme require only three lasers at 822 nm, 855 nm and 856 nm proceeded on the A 2П (ν′) ← X 2Σ+ (ν′′) transitions. The appeared intervening state A' 2Δ between the X 2Σ+ and A 2П states is the main challenge for laser cooling this molecule. In fact, the calculated vibrational branching loss ratio to the intermediate A' 2Δ state is almost negligible at a level of η < 4.5 × 10−9. Thus, BaF is a promising laser-cooling candidate with a relatively simple laser-cooling scheme.

Theoretical calculation of the low-lying doublet electronic states of the SrF molecule

The potential energy curves of the low-lying doublet electronic states in the representation 2s+1Λ(+/−) of the SrF molecule have been investigated by using the complete active space self-consistent field with multireference configuration interaction and multireference Rayleigh–Schrödinger perturbation theory methods. The harmonic frequency, ωe; the internuclear distance, Re; the dipole moment; and the electronic energy with respect to the ground state, Te, have been calculated for the considered electronic states. The eigenvalues, Ev; the rotational constants, Bv; and the abscissas of the turning points, Rmin and Rmax, have been investigated using the canonical functions approach. The comparison between the values of the present work and those available in the literature for several electronic states shows very good agreement. Nine new electronic states have been investigated here for the first time.

An ab initio study on the ground and low-lying doublet electronic states of linear C 2As

The present study is closely related to a recently published paper on the X ∼ 2 Π −1 2Δ spectral system of C 2As [S. Jerosimić, Lj. Stojanović, M. Perić, J. Chem. Phys. 133 (2010) 024307]. Here we report the results of ab initio calculations of the geometry, adiabatic excitation energies and electric dipole moments of the low-lying doublet electronic states of linear C 2As. We also discuss some peculiar details of the vibronic and spin–orbit structure in the X ∼ 2 Π and 1 2Δ states, being the subject of our previous paper. The results for transition moments between the vibronic energy levels within the ground electronic state are presented. The aim of the present study is to motivate new experimental studies on the title molecule and to facilitate the interpretation of the results of these investigations.

An ab initio study on the ground and low-lying doublet electronic states of SbO2

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying doublet electronic states of antimony dioxide (SbO(2)) employing a variety of ab initio methods, including the complete active space self-consistent field/multireference configuration interaction and the RCCSD(T) methods. Both large and small core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to aug-cc-pV5Z quality. Contributions from outer core correlation and off-diagonal spin-orbit interaction to relative electronic energies have been calculated. The ground electronic state of SbO(2) is determined to be the X (2)A(1) state, as is the case for dioxides of other lighter group 15 p-block (or group VA) elements. However, the A (2)B(2) and B (2)A(2) states are estimated to be only 4.1 and 10.7 kcalmole above the X (2)A(1) state, respectively, at the complete basis set limit. Reliable vertical excitation energies from the X (2)A(1) state to low-lying excited states of SbO(2) have been computed with a view to assist future spectral assignments of the absorption and/or laser-induced fluorescence spectra of SbO(2), when they become available.

Quantum chemical study of the electronic structure of NiCH2+ in its ground state and low-lying electronic excited states

The electronic structure of NiCH(2) (+), representative of transition metal carbene ions, is investigated by means of several methods of quantum chemistry. The relative stabilities of the four low-lying doublet electronic states ((2)A(1), (2)A(2), (2)B(1), and (2)B(2)) are determined at the coupled cluster singles and doubles level (CCSD) and triples level [CCSD(T) and CCSDT-3] with both a Hartree-Fock and density functional theory (Kohn-Sham) reference. The equation-of-motion coupled cluster for treatment of excited states in singles and doubles approximation (EOM-CCSD) is used to characterize the transition energies from the (2)A(1) electronic ground state to the low-lying doublet excited states. The (2)A(2) and (2)B(1) states are nearly degenerate, found to be separated by 940 cm(-1) at the EOM-CCSD level, in agreement with the CASSCF energy ordering. The (2)B(2) state is calculated to be higher in energy by more than 1.0 eV. The spin purity of the low-lying doublet and quadruplet states described by CCSD calculations based on the unrestricted open-shell Hartree-Fock reference is discussed.

Erratum: “Ab initio study of the electronic spectrum of C2H2+: Investigation of structure and spectra involving low-lying doublet electronic states” [J. Chem. Phys. 109, 3086 (1998)

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Ab initio study of the electronic spectrum of C 2H 2+. : II. Stretching potential energy surfaces for low-lying doublet electronic states

Results of ab initio MRD-CI calculations of the symmetric C–H, antisymmetric C–H and C–C potential energy curves for low-lying doublet electronic states of the acetylene cation are presented. Process of dissociation of C 2H 2 + out of the electronic states considered into the corresponding CH+CH + fragments is studied. The results of these calculations are employed in the subsequent work to interpret and predict the global structure of the spectra involving the species considered.

Ab initio study of the electronic spectrum of C 2H 2+. : I. Vertical spectrum and angular potential curves

Results of ab initio MRD-CI calculations of the vertical spectrum and trans-bending, cis-bending and torsional potential energy curves for low-lying doublet electronic states of the acetylene cation are presented. At the linear nuclear geometry these states correlate with X 2 Π u , 1 2 Σ + g , 1 2 Π g , 1 2 Φ g , 1 2 Σ + u , and 2 2 Π g , all of them being of predominantly valence character.

Ab initio study of the electronic spectrum of C2H2+: Investigation of structure of spectra involving low-lying doublet electronic states

Ab initio calculated potential energy surfaces for low-lying doublet electronic states of C2H2+ are employed to investigate the structure of spectra involving these species. Particular attention is paid to the X 2Πu, A 2Ag, and B 2Σu+ states arising by loss of an electron from one of the three uppermost molecular orbitals populated in the ground electronic state of the neutral molecule.

Ab initio study of the potential energy surfaces for the valence and Rydberg doublet electronic states of HNF

Results of large-scale configuration interaction calculations of the bending and N-F stretching potential curves for the low-lying doublet electronic states of HNF are presented. Special attention is paid to the investigation on valence and Rydberg character of the electronic states as well as the dissociation of HNF into NH and F atom.

Ab initio calculation of the potential surfaces and the electronic transition moments for the valence and Rydberg doublet electronic states of BH2

The bending and symmetric stretching potential curves for the low-lying doublet electronic states of the BH2 radical are calculated by means of the configuration interaction method. Special attention is paid to consideration of the interaction between valence and Rydberg-type species. The dissociation of BH2 in its various electronic states into H + B + H is studied. The results of calculations predict a complicated structure of both, the absorption and emission spectra caused by a number of avoided crossings between the excited states of the same symmetry in the geometry region close to the equilibrium geometry of the ground state.

Valence-specific open-shell coupled-cluster approach using a common vacuum. An application to doublet electronic states

We propose a simple valence-specific formulation of open-shell coupled-cluster theory using a single-exponential Ansätz for the wave operator. Formally resembling the well-known Fock space coupled-cluster approach, our method is easy to implement and free from spin contamination, but avoids the necessity to generate the cluster amplitudes hierarchically, starting from the zero-valence problem. Illustrative applications to the low-lying doublet electronic states of the F atom and the OH molecule are reported.

Ab initio calculation of the potential surfaces and the electronic transition moments for the valence and Rydberg doublet electronic states of HCO

Results of large-scale configuration interaction calculations of the bending and C–O stretching potential curves and the corresponding electric transition moments for the low lying doublet electronic states of HCO are presented. Special attention is paid to the study of interaction between valence- and Rydberg-type species.