Quartet Electronic States Research Articles

Electronic structure with dipole moment calculation of the low-lying electronic states of ZnBr molecule

Adiabatic potential energy curves of 19 low-lying doublet and quartet electronic states in the representation 2s+1Λ(±) of the zinc mono-bromide molecule ZnBr are investigated using high correlated ab initio calculations. For the bound states, the equilibrium internuclear distance Re, the harmonic frequency ωe, the rotational constant Be and the electronic transition energy with respect to the ground state Te have been calculated at the multireference configuration interaction (MRCI) level including single and double excitations with Davidson correction (+Q). Sixteen low-lying states are presented here for the first time. The ground state dissociation energy is also calculated. The comparison between the values of the present work are in agreement with those available in the literature.

Electronic structure with dipole moment calculation of the low-lying electronic states of the molecule ZnI

The potential energy curves of the low-lying 26 doublet and quartet electronic states in the representation 2s+1Λ(+/−) of the ZnI molecule have been investigated using the Complete Active Space Self Consistent Field (CASSCF) with Multi-Reference Configuration Interaction (single and double excitation with Davidson correction) MRCI+Q method and the second order multi-reference Rayleigh Schrödinger perturbation theory RSPT2-RS2 method. The harmonic frequency ωe, the internuclear distance Re, the static dipole moment, and the electronic energy with respect to the ground state Te have been calculated for the considered bound electronic states. The comparison between the values of the present work and those available in the literature shows a good agreement. Twenty-three electronic states are studied here for the first time.

Ab initio calculations of the electronic structure of the low-lying states for the ultracold LiYb molecule.

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.

Electronic Structure of the Cesium Oxide Molecule CsO

Adiabatic potential energy curves of 12 doublet and quartet lowest spinless electronic states of the molecule CsO have been investigated via ab initio CASSCF and MRCI (doublet and quartet excitations with Davidson correction) calculations. The spectroscopic constants such as vibrational harmonic frequency ωe, the internuclear distance at equilibrium Re, the rotational constant Be, and the electronic transition energy Te of the ground and the excited electronic states have been calculated by fitting the energy values around the equilibrium position to a polynomial in terms of the internuclear distance. The comparison of these values to those available in the literature shows a good agreement.

<i>Ab-Initio</i> Calculations of 27 Electronic States of the BP<sup>+</sup> Ion-Molecule

The theoretical investigation of the potential energy curves, in the representation 2s+1Λ(+/-), of the 27 low-lying Doublet and Quartet electronic states of the BP+ molecular ion has been performed with the methods in quantum chemistry, the Complete Active Space Self Consistent Field (CASSCF) and the Multireference Configuration Interaction (MRCI) calculations. The harmonic vibrational frequency ωe, the inter-nuclear distance at equilibrium Re, the rotational constant Be, the electronic energy with respect to the minimum ground state energy Te, and the permanent dipole moment have also been calculated. Twenty-three new electronic states have been investigated here for the first time. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. These investigated data can be a conducive to further work on BP+ molecular ion in both experimental and theoretical research.

Low-lying electronic states of the OH radical: Potential energy curves, dipole moment functions, and transition probabilities

The six doublet and the two quartet electronic states (2Σ+(2), 2Σ−, 2Π(2), 2Δ, 4Σ−, and 4Π) of the OH radical have been studied using the multi-reference configuration interaction (MRCI) method where the Davidson correction, core-valence interaction and relativistic effect are considered with large basis sets of aug-cc-pv5z, aug-cc-pcv5z, and cc-pv5z-DK, respectively. Potential energy curves (PECs) and dipole moment functions are also calculated for these states for internuclear distances ranging from 0.05 nm to 0.80 nm. All possible vibrational levels and rotational constants for the bound state X2Π and A2Σ+ of OH are predicted by numerical solving the radial Schrodinger equation through the Level program, and spectroscopic parameters, which are in good agreements with experimental results, are obtained. Transition dipole moments between the ground state X2Π and other excited states are also computed using MRCI, and the transition probability, lifetime, and Franck-Condon factors for the A2Σ+-X2Π transition are discussed and compared with existing experimental values.

Ab-initio potential energy curves of valence and Rydberg electronic states of the PO radical

This paper reports a theoretical study of the electronic states of PO radical. Highly correlated ab initio methods were used for mapping the potential energy curves. Internally contracted multi-reference configuration interaction method with the augmented correlation-consistent basis set (aV5Z) has been employed to carry out the study. After the nuclear motion treatment, the spectroscopic constants and the vibrational energy levels of the doublet and quartet electronic states are determined. The calculated values have been found in a good agreement with the existing experimental and theoretical results. The spin-orbit couplings between interacting states were also determined in the region where the crossings of the potential energy curves occurs. These couplings are capable to induce predissociation processes involving quartet states and producing P and O atoms at their ground and low lying excited electronic states. The theoretical vibrational spectrum was predicted using the Franck Condon factors and the transition moments integrals. The calculated spectrum shows intense peaks involving the Rydberg states in complete accordance with the experiment.

Shining new light on the multifaceted dissociative photoionisation dynamics of CCl4.

Internal energy selected carbon tetrachloride cations have been prepared by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet radiation. The threshold photoelectron spectrum shows a newly observed vibrational progression corresponding to the ν2(e) scissors mode of CCl4(+) in the third, B̃(2)E band. Ab initio results on the first four doublet and lowest-lying quartet electronic states along the Cl3C(+)-Cl dissociation coordinate show the B̃ state to be strongly bound, and support its relative longevity. The X̃(2)T1 and Ã(2)T2 cationic states, on the other hand, are barely bound and dissociate promptly. The C̃(2)T2 state may intersystem cross to the quartet ã state, which dissociates to a triplet state of the CCl3(+) fragment ion. This path is unique among analogous MX4(+) (M = C, Si, Ge; X = F, Cl, Br) systems, among which several have been shown to have long-lived C̃ states, which decay by fluorescence. The breakdown diagram, recorded here for the first time for the complete valence photoionisation energy range of CCl4, is interpreted in the context of literature based and CBS-QB3, G4, and W1U computed dissociative photoionisation energies. No Cl2-loss channel is observed in association with the CCl2(+) or CCl(+) fragments below the 2 or 3 Cl-loss reaction energies, and Cl2 loss is unlikely to be a major channel above them. The breakdown diagram is modelled based on the calculated dissociative photoionisation onsets and assuming a statistical redistribution of the excess energy. The model indicates that dissociation is not impulsive at higher energies, and confirms that the C̃(2)T2 state of CCl4(+) forms triplet-state CCl3(+) fragments with some of the excess energy trapped as electronic excitation energy in CCl3(+).

New insight into the electronic structure of iron(IV)‐oxo porphyrin compound I. A quantum chemical topological analysis

The electronic structure of iron-oxo porphyrin π-cation radical complex Por(·+) Fe(IV)=O (S-H) has been studied for doublet and quartet electronic states by means of two methods of the quantum chemical topology analysis: electron localization function (ELF) η(r) and electron density ρ(r). The formation of this complex leads to essential perturbation of the topological structure of the carbon-carbon bonds in porphyrin moiety. The double C=C bonds in the pyrrole anion subunits, represented by pair of bonding disynaptic basins V(i=1,2)(C,C) in isolated porphyrin, are replaced by single attractor V(C,C)(i=1-20) after complexation with the Fe cation. The iron-nitrogen bonds are covalent dative bonds, N→Fe, described by the disynaptic bonding basins V(Fe,N)(i=1-4), where electron density is almost formed by the lone pairs of the N atoms. The nature of the iron-oxygen bond predicted by the ELF topological analysis, shows a main contribution of the electrostatic interaction, Fe(δ+)···O(δ-), as long as no attractors between the C(Fe) and C(O) core basins were found, although there are common surfaces between the iron and oxygen basines and coupling between iron and oxygen lone pairs, that could be interpreted as a charge-shift bond. The Fe-S bond, characterized by the disynaptic bonding basin V(Fe,S), is partially a dative bond with the lone pair donated from sulfur atom. The change of electronic state from the doublet (M = 2) to quartet (M = 4) leads to reorganization of spin polarization, which is observed only for the porphyrin skeleton (-0.43e to 0.50e) and S-H bond (-0.55e to 0.52e).

The radical SeCl: A theoretical contribution to the characterization of its low-lying electronic states

All doublet and quartet electronic states correlating with the first dissociation channel of SeCl and some Rydberg states are investigated theoretically at the CASSCF/MRCI level of theory using extended basis sets, including the contribution of spin–orbit effects. The similarity of the potential energy curves with those of SeF suggests that spectroscopic constants for the ground (X 2Π) and the first excited quartet (a4Σ−) of SeCl could also be determined via an emission resulting from the reaction of selenium with atomic chlorine. The coupling constant of the ground state at Re is estimated as −1610cm−1. The potential energy curves calculated and the derived spectroscopic constants do not support the interpretation and assignment of the scarce transitions recorded experimentally as due to 2Π–2Π emissions. That the few observed lines might arise from transitions from the state b4∑1/2- to a very high vibrational level of the state a4∑1/2- is an open possibility, however, the number of vibrational states and the calculated ΔG1/2 differ significantly from the reported ones.

Electronic structure of the [MgO3]+ cation

Accurate ab initio calculations are performed to investigate the stable isomers of [MgO(3)](+) and its lowest electronic states at both molecular and asymptotic regions. The calculations are done using large basis sets and configuration interaction methods including the complete active space self-consistent field, the internally contracted multi-reference configuration interaction, the standard coupled cluster (RCCSD(T)) approaches and the newly implemented explicitly correlated coupled cluster method (RCCSD(T)-F12). The presence of three stable forms is predicted: a cyclic global minimum c-MgO(3)(+), which is followed by a quasi-linear isomer, l2-MgO(3)(+). A third isomer of C(s) symmetry (l1-MgO(3)(+)) is also found. Moreover, we computed the one-dimensional cuts of the six-dimensional potential energy surfaces of the lowest doublet and quartet electronic states of [MgO(3)](+) along the R(MgO) and R(OO) stretching coordinates covering both the molecular and the asymptotic regions. These curves are used later for discussing the metastability of this cation and to propose plausible mechanisms for the Mg(+) + O(3) atmospherically important ion-molecule reaction and related reactive channels.

Theoretical investigations of the MgO+ cation: spectroscopy, spin–orbit coupling and single ionization spectrum

We used ab initio methodology for the computation of the potential energy curves of the doublet and quartet electronic states of the MgO+ cation correlating with the four lowest dissociation limits. Using these highly correlated wavefunctions, we calculated their spin–orbit coupling and transition moments. We deduced an accurate set of spectroscopic constants for this cation. Most of the data relative to the electronic excited states of this cation are predictive in nature. Moreover, our potentials, transition moments and spin–orbit coupling evolutions are incorporated into Fermi golden rule calculations to deduce the natural lifetimes of the lowest MgO+(12Σ+) ro-vibrational levels. Finally, our potentials were used for the prediction of the single ionization spectrum of MgO.

Theoretical calculation of the low-lying quartet states of the CrF molecule

The potential energy curves have been investigated for the 11 lowest quartet electronic states in the 2s+1Λ± representation below 28 000 cm–1 of the molecule CrF via CASSCF and MRCI (single and double excitations with Davidson correction) calculations. Eight electronic states have been studied theoretically for the first time. The harmonic frequency ωe, the internuclear distance re, the rotational constant Be, the electronic energy with respect to the ground state Te, and the permanent dipole moment μ have been calculated. By using the canonical functions approach, the eigenvalues Ev, the rotational constant Bv, and the abscissas of the turning points rmin and rmax have been calculated for electronic states up to the vibrational level v = 38. The comparison of these values to the theoretical results available in the literature shows a very good agreement.

The Evolution of Bonding and Thermodynamic Properties of Boron‐Doped Small Carbon Clusters: An Ab Initio Study

Theoretical studies on BC(n) (n=1-6) clusters are carried out using density functional theory, Møller-Plesset second-order perturbation theory (MP2), coupled-cluster calculations including up to triple excitations (CCSD(T)), and higher-level approaches. All possible isomers depending on the positions of the boron atom are generated and the lowest-energy isomers are determined for doublet and quartet electronic states. The three potential evolution paths of the clusters are determined as a function of their size. The energetic and electronic consequences for the increased size of structures differ significantly, which leads to representatives of the ground electronic state from different structural groups. The ab initio calculated thermal functions allow enhancements to the available atomization energies and improve the agreement between the calculated and experimental heat content.

The electronic states of SeF: A reinterpretation of the chemiluminescent emission of the reaction of selenium with fluorine

The low-lying doublet and quartet electronic states of the species SeF correlating with the first dissociation channel are investigated theoretically at a high-level of electronic correlation treatment, namely, the complete active space self-consistent field/multireference single and double excitations configuration interaction (CASSCF/MRSDCI) using a quintuple-zeta quality basis set including a relativistic effective core potential for the selenium atom. Potential energy curves for (Lambda+S) states and the corresponding spectroscopic properties are derived that allows for an unambiguous assignment of the only spectrum known experimentally as due to a spin-forbidden X (2)Pi-a (4) summation (-) transition, and not a A (2)Pi-X (2)Pi transition as assumed so far. For the bound excited doublets, yet unknown experimentally, this study is the first theoretical characterization of their spectroscopic properties. Also the spin-orbit coupling constant function for the X (2)Pi state is derived as well as the spin-orbit coupling matrix element between the X (2)Pi and a (4) summation (-) states. Dipole moment functions and vibrationally averaged dipole moments show SeF to be a very polar species. An overview of the lowest-lying spin-orbit (Omega) states completes this description.

H2NSi radical: structures, isomerization pathways and electronic states characterization

Using state-of-the-art theoretical methods, the stable isomers of H2NSi which are relevant for astrophysics, astrochemistry and ammonia silicon surface chemistry, were investigated. These computations are performed using configuration interaction ab initio methods and the aug-cc-pVQZ and cc-pVQZ basis sets. Calculations confirm the existence of three stable isomers: H2NSi, trans-HSiNH and H2SiN. The intramolecular isomerization and the H-abstraction reaction pathways on the lowest doublet potential energy surfaces are given. Insight into the pattern of the lowest doublet and quartet electronic states of these molecular species are also presented.

Theoretical study with vibration-rotation and dipole moment calculations of quartet states of the CrCl molecule

The potential energy curves have been investigated for the 10 lowest quartet electronic states in the 2s+1Λ± representation below 30,000 cm−1 of the molecule CrCl via CASSCF and MRCI (singly and doubly excitation with Davidson correction) calculations. The harmonic frequency ωe, the internuclear distance re, the rotational constant Be, the electronic energy with respect to the ground state Te, and the permanent dipole moment μ have been calculated. By using the canonical functions approach, the eigenvalues Ev, the rotational constant Bv, and the abscissas of the turning points rmin and rmax have been calculated for the considered electronic states up to the vibrational level v = 19. Seven electronic states have been studied here theoretically for the first time. The comparison of these values to the theoretical results available in the literature shows a good agreement. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

Spin-unrestricted DFT-X3LYP/6-311++G(d,p) calculations have been performed on a series of complexes of the form [Co(H(2)O)(6-n)(NH(3))(n)](2+) (n = 0-6) to examine their equilibrium gas-phase structures, energetics, and electronic properties in their quartet electronic ground states. In all cases Co(2+) in the energy-minimised structures is in a pseudo-octahedral environment. The calculations overestimate the Co-O and Co-N bond lengths by 0.04 and 0.08 A, respectively, compared to the crystallographically observed mean values. There is a very small Jahn-Teller distortion in the structure of [Co(H(2)O)(6)](2+) which is in contrast to the very marked distortions observed in most (but not all) structures of this cation that have been observed experimentally. The successive replacement of ligated H(2)O by NH(3) leads to an increase in complex stability by 6 +/- 1 kcal mol(-1) per additional NH(3) ligand. Calculations using UB3LYP give stabilisation energies of the complexes about 5 kcal mol(-1) smaller and metal-ligand bond lengths about 0.005 A longer than the X3LYP values since the X3LYP level accounts for the London dispersion energy contribution to the overall stabilisation energy whilst it is largely missing at the B3LYP level. From a natural population analysis (NPA) it is shown that the formation of these complexes is accompanied by ligand-to-metal charge transfer the extent of which increases with the number of NH(3) ligands in the coordination sphere of Co(2+). From an examination of the topological properties of the electron charge density using Bader's quantum theory of atoms in molecules it is shown that the electron density rho(c) at the Co-O bond critical points is generally smaller than that at the Co-N bond critical points. Hence Co-O bonds are weaker than Co-N bonds in these complexes and the stability increases as NH(3) replaces H(2)O in the metal's coordination sphere. Several indicators, including the sign and magnitude of the Laplacian of the charge density nabla(2)rho(c), the ratio of the local potential and kinetic energy densities, |V(c)|/G(c), the sign of the total energy density H(c), and the delocalisation index delta(Co,X), X = O, N, are used to show that whilst the metal-ligand bonds are predominantly ionic in nature, they gain covalent character as NH(3) replaces H(2)O, and the Co-N bond is significantly more covalent than the Co-O bond. We have shown that the delocalisation index delta(Co,X), X = O, N, is strongly correlated with the zero-point corrected stabilisation energy E demonstrating that delta can be used as a measure of the bond stability in these complexes.

DFT study of the reaction of NO 2( 2A 1) with CO( 1Σ +) mediated by V +

The mechanism of the reaction of NO 2( 2A 1) + CO( 1Σ +) → NO( 2Π) + CO 2( 1 Σ g + ) mediated by V + has been investigated by means of DFT-UB3LYP/6-311+G(2d) level of theory. The potential energy surfaces (PESs) of [NO 2, V] + and [VO, CO] + were explored in detail in singlet and triplet with doublet and quartet electronic states. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and the strongly crossing behavior on the transition state (TS) area was shown. Finally, the actions of frontier molecular orbitals in CPs have been illuminated briefly. These theoretical results can act as a guide to further theoretical and experimental researches.

Electronic spectrum of 2‐pyridone+: Ab initio and time‐dependent density functional calculations

AbstractIn a comparative study, the doublet and quartet electronic states of the 2‐pyridone+ cation are calculated using the PBE0/6‐311+G(d,p) technique and the CASSCF and MRCI(+Q) methods in connection with the cc‐pVDZ and cc‐pVTZ Dunning's basis sets. Our data show that TD‐DFT describes quite well the vertical excitation energies of these electronic states, whereas, multiconfiguration methods should be used for the investigation of the fragmentation and the dynamics of this molecular species. This is related to the change of the nature of the wavefunction of these electronic states along the corresponding reactive coordinates not accounted for by TD‐DFT methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010