Adiabatic Potential Energy Research Articles

Theoretical studies of the excited electronic states of the molecule ScLi and its ions ScLi± with a feasibility study of laser cooling

For the transition metal lithides ScLi and ScLi±, the adiabatic potential energy and the static and transition dipole moment curves of the low-lying electronic states in the representation 2 s+1Λ(+/−) have been investigated. The spectroscopic constants, the electronic transition energy with respect to the ground state Te, the internuclear distance Re, the harmonic frequency ωe, the rotational constant Be, the permanent dipole moment µe, and the dissociation energies De have been computed for the bound and excited states. Using the canonical function approach, these calculations have been followed by a rovibrational calculation from which the rovibrational constants Ev, Bv, and Dv and the abscissas of the turning points Rmin and Rmax for the investigated bound states are calculated. A feasibility study of laser cooling of ScLi and its ions ScLi± has been done. New 62 electronic states have been investigated in the present work for the first time. No useful cooling scheme was found for those molecules.

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

A novel type of sub-lattice of the Jahn-Teller (JT) centers was arranged in Ti-doped barium hexaferrite BaFe12O19. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are Fe3+ in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor Ti substitution converts the ions to Fe2+ predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the Eotimes e problem of the JT effect. The arranged JT complexes, Fe2+O4, their adiabatic potential energy, non-linear and quantum dynamics, have been studied by means of ultrasound and terahertz-infrared spectroscopies. The JT complexes are sensitive to external stress and applied magnetic field. For that reason, the properties of the doped crystal can be controlled by the amount and state of the JT complexes.

Substitution effects on 1,3-disubstituted imidazol-2-ylidenes and 1,3-diarylimidazol-2-ylidenes revisited: a theoretical study at DFT level

Effect of substituents on philicity and stability of 1,3-disubstituted imidazol-2-ylidenes and 1,3-diarylimidazol-2-ylidenes was assessed using the following calculations: adiabatic electron affinity and adiabatic ionization potential, global electrophilicity and differential orbital energy scales for philicity, and ΔES–T, ΔEHyd, ΔEiso, and ΔEH–L for stability, with the aid of density functional theory and the results were then compared with each other. In the case of 1,3-disubstituted imidazol-2-ylidene, the carbene with CH3 group has the highest nucleophilic character considering all the above scales and the highest thermodynamic stability. 1,3-Diarylimidazol-2-ylidenes with CH3O and NH2 groups have high-nucleophilic properties and high-stability; their ΔEiso values are also greater than 377 kJ/mol which means that they may be reasonable synthetic targets. While, the presence of electron donating groups at 1,3-disubstituted imidazol-2-ylidene results in ΔEiso > 377 kJ/mol. Nucleophilicity of 1,3-diarylimidazol-2-ylidenes is, to some extent, greater than that of 1,3-disubstituted imidazol-2-ylidenes.

Theoretical investigation of two model systems for molecular photoswitch functionality. I. 2-(4-nitropyrimidin-2-yl)ethenol

The ground and five lowest-lying electronically excited singlet states of 2-(4-nitropyrimidin-2-yl)ethenol (NPE) have been studied theoretically using the complete active space self-consistent-field (CASSCF), Møller-Plesset second-order perturbation theory (MP2) and second-order multi-configurational perturbation theory (CASPT2) methods. The molecule can be regarded as being composed of a frame and a crane component and is characterised by the existence of two planar minima of similar energy on the ground-state potential energy (PE) surface. This work explores the possibility of an excited-state intramolecular hydrogen transfer (ESIHT) process in NPE. A hypothetical reaction coordinate has been constructed for NPE. State-averaged CASSCF and CASPT2 calculations of the six lowest-lying singlet states have been performed for the isomerisation. Adiabatic and simplified quasi-diabatic PE and transition dipole moment functions have been constructed. The computations indicate that there exist substantial barriers for the rotation process on the adiabatic PE surfaces of all the five excited states investigated. The six quasi-diabatic electronic states considered here decompose into two classes based on whether the electronic wave functions depend weakly or strongly on the nuclear displacement, subject to the effect of the torsion on relevant molecular orbitals.

The early years of Pierre: importance of his work for Astrophysics and other fields of Physics

A brief review is given of the pioneering work of Pierre during the years 1974-1981, during which time he investigated the state selective nature of electron capture by multiply charged ions under interstellar conditions. The various stages on the development of the methods used are presented: adiabatic representation and potential energy surfaces, non-adiabatic matrix elements, diabatic transformation, extraction of the S-matrix, optimal choice of reaction coordinates. Finally some very recent results on D + +H 2 → H + +HD ion-molecule reactions inspired by the early work are presented.

Theoretical study of the electronic structure of LiX and NaX (X = Rb, Cs) molecules

AbstractAdiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels have been computed for the lowest electronic states of alkali dimers LiX and NaX (X = Rb, Cs). Calculations have been carried with the use of an ab initio approach with core‐potential potentials and full‐valence configuration. Thus, these systems are treated as two‐electron systems. A good agreement is obtained for some lowest states of the molecules studied with available theoretical works. The existence of numerous avoided crossings between electronic states for 1Σ symmetries is related to the charge‐transfer process in each molecule between its two ionic systems (Li+X−, Li−X+) and (Na+X−, Na−X+). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Electronic states of CsLi and CsLi+ molecules

Configuration interaction calculations have been carried out on electronic states of the CsLi molecule and the CsLi+ cation. Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels are presented for the lowest states of 1,3Σ+, 1,3Π, and 1,3Δ symmetries of the alkali dimer CsLi molecule dissociating into Cs (6s, 6p, 5d, 7s, and 7p) + Li (2s, 2p, 3s, 3p, and 3d) as well as for the lowest 2Σ+, 2Π, and 2Δ electronic states of the CsLi+ cation dissociating into Li (2s, 2p, 3s, 3p, and 3d) + Cs+ and Li+ + Cs (6s, 6p, 5d, 7s, and 7p). The results of the present many-electron configuration interaction calculations on the cation support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s2) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some of the lowest states of the CsLi and CsLi+ molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries is related to a charge transfer process between the two ionic CsLi+ and LiCs+ systems.

X, A, B, C, and D States of the C6H5F+ Ion Studied Using Multiconfiguration Wave Functions

Electronic states of the C6H5F+ ion have been studied within C2v symmetry by using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with an atomic natural orbital basis. Vertical excitation energies (Tv) and relative energies (Tv') at the ground-state geometry of the C6H5F molecule were calculated for 12 states. For the five lowest-lying states, 1(2)B1, 1(2)A2, 2(2)B1, 1(2)B2, and 1(2)A1, geometries and vibrational frequencies were calculated at the CASSCF level, and adiabatic excitation energies (T0) and potential energy curves (PEC) for F-loss dissociations were calculated at the CASPT2//CASSCF level. On the basis of the CASPT2 T0 calculations, we assign the X, A, B, C, and D states of the ion to 1(2)B1, 1(2)A2, 2(2)B1, 1(2)B2, and 1(2)A1, respectively, which supports the suggested assignment of the B state to (2)(2)B1 by Anand et al. based on their experiments. Our CASPT2 Tv and Tv' calculations and our MRCI T0, Tv, and Tv' calculations all indicate that the 2(2)B1 state of C6H5F+ lies below 1(2)B2. By checking the relative energies of the asymptote products and checking the fragmental geometries and the charge and spin density populations in the asymptote products along the CASPT2//CASSCF PECs, we conclude that the 1(2)B1, 1(2)B2, and 1(2)A1 states of C6H5F+ correlate with C6H5+ (1(1)A1) + F (2P) (the first dissociation limit). The energy increases monotonically along the 1(2)B1 PEC, and there are barriers and minima along the 1(2)B2 and 1(2)A1 PECs. The predicted appearance potential value for C6H5+ (1(1)A1) is very close to the average of the experimental values. Our CASPT2//CASSCF PEC calculations have led to the conclusion that the 1(2)A2 state of C6H5F+ correlates with the third dissociation limit of C6H5+ (1(1)A2) + F (2P), and a preliminary discussion is presented.

Theoretical study of the electronic states and transition dipole moments of the LiK + molecule

The adiabatic potential energy, the spectroscopic constants and the transition dipole moments of the lowest electronic states of the LiK + molecule, dissociating into Li(2 s, 2 p, 3 s, 3 p, 3 d, 4 s, and 4 p) + K + and Li + + K(4 s, 4 p, 5 s, 3 d, 5 p, 4 d, and 6 s), have been investigated. We have used an ab initio approach involving a non-empirical pseudopotential for the Li (1 s 2) and K (1 s 22 s 22 p 63 s 23 p 6) cores and core valence correlation correction. A very good agreement has been obtained for the ground state for the spectroscopic constants with the available theoretical works. The transition dipole moment from X 2Σ, 2 2Σ, 3 2Σ, and 4 2Σ states to higher excited states have been determined. Numerous avoided crossing between electronic states of 2Σ and 2Π symmetries, have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Li +K and LiK +.

Antiproton-hydrogen scattering at low-eV energies

In the scattering of negative particles other than the electron by atoms at lab-frame energies around 10 eV, an elastic process termed “brickwall scattering” might lead to a high probability for scattering angles around 180°. For an antiproton slowing in hydrogen, this backward scattering would result in the loss of nearly all of its energy in a single collision, since it and a hydrogen atom have nearly the same mass. Such energy loss would have a significant effect on the energy distribution of antiprotons at energies where capture by the protons of hydrogen is possible and might, thereby, affect the capture rate and the distribution of capture states. In the semiclassical treatment of the problem with an adiabatic potential energy, brickwall scattering is indeed present, and with a substantial cross section. However, this model appears to underestimate inelastic processes. Based on calculations for negative muons on hydrogen atoms, these processes appear to occur for about the same impact parameters as brickwall scattering and thus substantially reduce its effect.

Potential energy curves of (HeNe)2+. Electronic couplings and transition dipole moment calculations

The authors present the determination of adiabatic and quasiadiabatic potential energy curves of the ground state and of some low-lying excited states of the molecular system (HeNe)2+. An extension of Levy's method for disadiabatisation is developed in the study of the 1 Sigma + states. The potential curves and the electronic couplings calculated in this work are useful for the analysis of collisional processes, in particular for the charge transfer reaction Ne2++He to Ne++He+. The Einstein coefficients Ai,j needed for this study have also been calculated.

Rotronic Jahn-Teller effect for diatomic molecular impurities at cubic sites in ionic crystals

The theory of hindered rotation of diatomic molecular impurities at cubic sites in ionic crystals is generalized to account for the orbital degeneracy of the molecule, with use of a crystal-field approach. This theory explains the observed 110g orientations of the molecular axis, the orientations of the $\ensuremath{\pi}$ orbitals along either 110g or 100g axes, and the dominance of 90\ifmmode^\circ\else\textdegree\fi{} tunneling in some cases, even using only the lowest-order term in the octahedral crystal field ($l=4$). It is shown that the coupling of the degenerate orbital to the rotation in the crystal field generates an instability if the molecular axis is parallel to a 111g direction, leading to a Jahn-Teller effect resulting from rotational-electronic (rotronic) coupling. Analytic expressions for the lowest branch of the adiabatic potential energy as a function of the orientation of the molecular axis are calculated for $\ensuremath{\Sigma}$, $\ensuremath{\Pi}$, and $\ensuremath{\Delta}$ states, and the orbital wave functions are determined for $\ensuremath{\Pi}$-state molecules. The case of a diatomic molecular impurity at a site of tetrahedral symmetry is discussed.

Absorption line shape of a dynamical Jahn-Teller Center. Strong-interaction limit

The dynamic Jahn-Teller effect, induced in a localized center by light absorption and due to a singlet-multiplet electronic transition, is studied in the strong-interaction limit (SIL) of the electron-phonon interaction. The absorption line shape $R(\ensuremath{\omega})$ is examined in the framework of the linear-response theory and the role of the host crystal in fading the correlations among the phonons associated to the electronic excitation is taken into account. $R(\ensuremath{\omega})$ is deduced by using the Feynman-paths method and the most significant contribution from each path, when working in the SIL, is identified. It is shown that the so-called semiclassical model (SCM) corresponds to considering only the Markovian many-phonon processes in the motion of the crystal phonons coupled to the Jahn-Teller excited electron. It is also shown why a refined version of the SCM leads to an effective Hamiltonian, where the adiabatic potential energy is related only to a few interaction modes and effective frequencies. In particular, the interaction modes are found to be stochastic, and not dynamical, variables. A correction to the well-known SCM Toyozawa-Inoue expression is found and discussed. Finally, the phonon quantum effects on $R(\ensuremath{\omega})$ in the SIL and beyond the SCM are introduced and commented on.