The low-energy level structure and the electromagnetic properties of191Ir and193Ir

TheM 1 andE 2 reduced transition probabilities in¹⁹¹Ir and¹⁹⁹Ir have been calculated on the weak particle-core coupling model. The static moments of the ground state and the first three low-lying excited states have been computed. The theoretical values are in good agreement with the experimental results, in particular, the existing discrepancy between the theoretical and the experimental value for the magnetic moment of the first excited 5/2⁺ state, in both these nuclei, has been removed. The predicted sign of the quadrupole moment of the 2⁺ state in the neighbouring even-even nuclei is consistent with the results reported for Platinum nuclei. The level structure of both these nuclei has been calculated assuming the particle-core interaction to be dipole-dipole and quadrupole-quadrupole type.     

Core excitation in79Br and81Br

TheE2 andM1 reduced transition probabilities between the low lying levels, in the case of⁷⁹Br and⁸¹Br, have been calculated on the core-excitation model. To account for the observed M1 transition probabilities admixture among the like spin states is considered. In addition, the ground state static moments have been computed. For the same amount of admixture among the like spin states, a good agreement with the experimental results is obtained, for both⁷⁹Br and⁸¹Br. The results are compared with other existing theoretical calculations. From our analysis, we obtain, the quadrupole moment of the first excited 2⁺ state in the neighbouring even-even nuclei. It is in good agreement with the value calculated on the basis of the anharmonic vibrational model.     

Ab initio study of ground and low-lying excited states of MgLi and MgLi+ molecules with valence full configuration interaction and MRCI method

The ground and low-lying excited states of MgLi and MgLi⁺ molecules have been investigated. The potential energy curves and the permanent and transition dipole moments of the MgLi and MgLi⁺ molecules are determined making use of the multi-reference configuration interaction and valence full configuration interaction with large basis sets. The core–valence correlation and scalar relativistic correction are also taken into account with aug-cc-pCVQZ basis set and the third-order Douglas–Kroll Hamiltonian approximation, respectively. The transition dipole moments are used to evaluate the radiative lifetimes of the vibrational levels for the low-lying excited states of the MgLi and MgLi⁺ molecules. The derived spectroscopic constants of the ground and low-lying excited states are in good agreement with available experimental and theoretical works.     

Quasi-relativistic treatment of the low-lying KCs states

The potential energy curves, permanent and transition dipole moments as well as spin-orbit and angular coupling matrix elements between the KCs electronic states converging to the lowest three dissociation limits were evaluated in the basis of the spin-averaged wavefunctions corresponding to pure Hund’s coupling case (a). The quasi-relativistic matrix elements have been obtained for a wide range of internuclear distance by using of small (9-electrons) effective core pseudopotentials of both atoms. The core-valence correlation has been accounted for a large scale multi-reference configuration interaction method combined with semi-empirical core polarization potentials. The static dipole polarizabilities of the ground X¹Σ⁺ and a³Σ⁺ states were extracted from the closed-shell coupled-cluster energies by the finite-field method. Among the singlet and triplet Σ⁺ states manifold the pronounced avoided crossing effect between repulsive walls of the (2,3)³Σ⁺ states has been discovered and analyzed by finite-difference calculation of radial coupling matrix elements. The resulting transition dipole moments and potentials were used to predict radiative lifetimes and emission branching ratios of excited vibronic states while the calculated angular coupling matrix elements were transformed to Λ-doubling constants of the (1,2)¹Π states and magnetic g-factor of the ground state. The accuracies of the present results are discussed by comparing with experimental data and preceding calculations.     

The microwave spectrum of difluoroacetic acid

Transitions due to two conformations have been observed in the microwave spectrum of difluoroacetic acid. In both rotamers the carboxylic hydrogen atom is cis to the CO bond, whereas the other hydrogen atom is either trans or gauche with respect to the CO bond. By means of isotopic substitution of the hydrogen and oxygen atoms a serious deviation of local symmetry in the CHF₂ group is deduced for the gauche form. This is thought to be an artifact of the substitution method, although no satisfactory explanation can be given. In torsionally excited states of the gauche conformation, doublet splittings were observed due to tunneling through a barrier of 190 ± 10 cm^?1. For the second excited state a satisfactory treatment could be given, but for the third excited state large differences between observed and calculated transition frequencies remained. A computer program to account for the internal rotation in asymmetric molecules was written, and it was shown qualitatively that interactions with excited states of the trans conformation could very well be responsible for the discrepancies. From intensity measurements the energy difference E(gauche) - E(trans) was found to be 370 ± 180 cm^?1. The large uncertainty is due to the failure of attempts to determine the dipole moments experimentally; they were estimated from an improved set of bond moments which was derived from related compounds. Both energy difference and dihedral angles are at variance with the results of an earlier electron diffraction investigation.     

Static and dynamic quadrupole moments of high-spin isomers in the Pb-region

Quadrupole moments of high-spin isomers in the Pb-region are studied by using core polarization charges induced by the coupling of single-particle states to giant resonances. We found that the core polarization charges are enough to reproduce the observed quadrupole moments of the isotones with neutron number N=126 quantitatively without any intrinsic deformation. The mass number dependence of the quadrupole moments in the Rn-isotopes is also discussed by taking into account the configuration mixing involving the neutron excited first 2⁺ state.     

Nuclear structure calculations with a density-dependent force in 208Pb

Excitation energies and excitation probabilities in ²⁰⁸Pb of the low lying states as well as of strongly collective high lying states (generalized multipole resonances) are calculated, using a large configuration space and a density dependent interaction. Within the extended theory of finite Fermi systems moments of excited states and transition probabilities between excited states are calculated. The theoretical results are in fair agreement with the experimental values.     

Model calculation of the electronic structure and spectroscopy of Hg2

Energy curves and transition moments of the excited valence states of Hg₂ were obtained in a model calculation based on calculated Mg₂ energy levels and the assumption that the asymptotic spin-orbit matrix elements for the Hg atom are applicable to the molecular states. The spin-orbit and orbital-rotational interaction of the excited states of Hg₂ is analyzed in both a Hund's case (c) and (a) representation. The intermediate (a) → (c) transition moments are obtained as a function of the internuclear distance. The effect of the orbital-rotational interaction which introduces Hund's case (b) and (e) couplings is found to be small for transitions among excited states under the conditions normally encountered for populating excimer states.Using the energy level positions and transition moments, the observed spectra and predicted spectra are compared for both radiative transitions including the ground state and among the excited states. The lifetime of the $\text{1}{}_{\mathrm{u}}\text{(}{}^3\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{)}$ excimer state is calculated to be 1.4 μsec with the 335 nm band assigned to the $\text{1}{}_{\mathrm{u}}\text{→ X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ transition. The 485 nm bands cannot be assigned to any Hg₂ transitions. Strong bound-continuum absorptions are predicted for the 485 nm bands. On the other hand, the 335 nm emission is predicted to be absorbed by bound-bound transitions only.     

A complete neglect of differential overlap (CNDO2) study of the electronic structure of HCCCHO

The spectral properties of the ground (¹A′) and the lowest triplet excited state (³A″) of propynal (HCCCHO) molecule has been calculated using the semiempirical SCF scheme of Pople, Santry, and Segal. The results show that the transition energies, the diploe moments, and the equilibrium geometries are in good agreement with experiment, but the force constants are generally two to three times overestimated.     

Theoretical study of molecular properties of low-lying electronic excited states of H2O and H2S

Geometries, excitation energies, dipole moments and dipole polarisability tensor components of the ground and four lowest excited states ³ B ₁, ¹ B ₁, ³ A ₂, ¹ A ₂ of the H₂O and H₂S molecules were calculated at the CASSCF, CASPT2, CCSD and CCSD(T) level of approximation. Vertical excitation and equilibrium transition energies of these states, having the Rydberg character, are reported too. Properties of both molecules in the ground and in low lying excited states are compared and discussed from the point of view of their molecular electronic structure. Upon excitation we observe dramatic changes of dipole moments and polarisabilities with respect to the ground state. We stress the change of the polarity of H₂O in all excited states accompanied by the enhancement of the dipole polarisability by an order of magnitude. Large, even if less pronounced, are changes of electric properties of H₂S in its excited states. Dipole moments and dipole polarisabilities of ³ B ₁, ¹ B ₁ states of H₂S and H₂O behave quite analogously in comparison to their respective ground state. The general pattern of properties for both molecules in their ³ A ₂ and ¹ A ₂ excited states is more different due to a pronounced participation of the sulphur d-orbitals in these states of the H₂S molecule.     

The lowest metal-to-bipyridine charge-transfer excited state of [Cr(2,2′-bipyridine)(CO)4]

The DV-Xα molecular-orbital calculations have been carried out on [Crbpy(CO)₄](bpy,2,2′-bipyridine) and its electron attachment and detachment products. The one-electron attachment of [Crbpy(CO)₄] yields a complex of bipyridine anion radical, while the one-electron detachment results in ionization of the central metal atom. The lowest excited state of [Crbpy(CO)₄] is the metal-to-ligand charge-transfer (MLCT) excited state which consists of the bipyridine anion radical and the central metal ionized. The transition-state calculation predicts the lowest MLCT excited states at around 23～30×10³ cm^?1 and the lowest bipyridine (π,π^*) excitations at 36×10³ cm^?1 and 42～45×10³ cm^?1. The calculation also concludes that the MLCT excitation induces a counter migration of the other electrons not directly involved in the charge-transfer excitation. The configuration-interaction calculations predict the lowest MLCT excited singlet states at around 21～35×10³ cm^?1 and the lowest bipyridine (π, π^*) excited singlet states at 42～62×10³ cm^?1, while the emissive lowest MLCT triplet state is at 17×10³ cm^?1. The transition moments evaluated with the transition-state wavefunctions can reproduce qualitatively the observed absorption spectral profile. The intensity of the MLCT transitions is obtained from the allowed (π, π^*) transitions of coordinated bipyridine but is not due to the intrinsic transition moments of MLCT excitations.     

Fourier transform spectroscopy of CrO: Rotational analysis of the A5Σ-X5Π (0,0) band near 8000 cm−1

The emission spectrum of CrO has been investigated by Fourier transform spectroscopy in the near infrared. New weak electronic bands have been found in the 6000- to 10 000-cm^?1 region, the strongest of which, near 8000 cm^?1, is shown to be the (0,0) band of a ⁵Σ-⁵Π transition where the ⁵Π lower state is the ground state. Fifty branches have been assigned in this band, which have permitted the first detailed characterizations of quintet electronic states in the gas phase. Accurate values have now been obtained for the spin-orbit coupling and Λ-doubling intervals in the ground state (which could only be estimated in the previous laser-induced fluorescence work in the visible region by Hocking et al. [Canad. J. Phys.58, 516–533 (1980)]). The relative branch intensities are not consistent with those calculated for a pure ⁵Σ-⁵Π(a) transition, and indicate considerable spin-orbit contamination such that there are interference effects between two or more competing transition moments. It is not known whether the ⁵Σ excited state is ⁵Σ⁺ or ⁵Σ^?.     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

Mössbauer conversion spectroscopy: Measurements on the first excited states of180, 182W and145Pm

The Mössbauer Conversion (MBC) Spectroscopy and criteria for its useful application are discussed and compared with other MB-techniques. By help of the MBC spectroscopy the isomer shift of the first excited state in¹⁸²W was measured and a change in radius ?0.05 · 10^?4>Δ 〈r ²〉/〈r ²〉>?0.28 · 10^?4 derived. The ratio of quadrupole moments of first excited states in¹⁸⁰W and¹⁸²W turns out to be¹⁸⁰ Q/¹⁸² Q=0.976 (30). Due to the excellent statistical quality of the spectra the interference parameter of the 100keVE2 transition in¹⁸²W could be determined to 2β=0.0165(9) for theL-shell. The MB-effect for the 61 keV transition in the instable¹⁴⁵Pm has been detected for the first time. A widthΛ _exp=2.15(58) mm/s was obtained.     

A K-harmonics description of 16O breathing mode

We calculate the properties of the ¹⁶O breathing mode in a K_minK-harmonics calculation. The breathing mode has single particle quantum numbers that are identical to the nucleon quantum numbers in the ground state. We calculate an excitation energy of 27 MeV, and a monopole transition matrix element of 7.21 fm². Six excited monopole states are calculated to be bound in ¹⁶O, with k equal to K_min. These states exhaust 90 % of the isoscalar monopole sum rule. The first excited K_min state, the breathing mode, exhausts 68 % of the isoscalar sum rule.     

Electronic transition moments between excited singlet states of the H2 molecule

The twelve transition moments which connect each of the three ¹Σ_g⁺ states EF, GK, and $\text{H}\text{H}$ with the three ¹Σ_u⁺ states B,B′, $\text{B″}\text{B}$ and with the state C¹Π_u were computed in the range of internuclear distances 1.25 ≤ R ≤ 15 a.u. using accurate electronic wavefunctions. The relative phases of the wavefunctions, which determine the signs of the transition moments, were consistently defined at all R values. The strong R dependences of the transition moments reflect the R-dependent changes in electronic character of the states involved in these transitions. At large R values the ¹Σ_g⁺-¹Σ_u⁺ transition moments are dominated by the two-electron charge resonance in the ionic configuration H⁺ + H^? whose transition moment is $\text{M(R) ? R}$.     

Theoretical investigation of the molecular structure and transition dipole moments of the NaK low lying electronic states

The electronic structure and the spectroscopic constants of the low lying electronic states of the NaK⁺ ionic molecule have been determined through using an ab initio approach involving a non-empirical pseudopotential for the Na and K cores and core valence correlation correction. The potential energy of nearly 26 electronic states of ²Σ⁺, ²Π, and ²Δ symmetries has been calculated up to their dissociation limit Na(4d) + K⁺ and Na⁺ + K(6s). Their spectroscopic constants (R_e, D_e, T_e, ω_e, ω_eχ_e, and B_e) are derived and compared with the few available theoretical studies. A good agreement has been found for the ground state and few excited states with previous works. New potential energy curves were presented, for the first time, for the higher excited states. Numerous avoided crossing between electronic states of ²Σ⁺, ²Π symmetries have been localized and analyzed. Their existences are related to the charge transfer between the two ionic molecules Na⁺K and NaK⁺. Furthermore, we have determined the transition dipole moments for several states and analyzed the avoided crossings related to charge transfer between alkaline atoms.     

Photoinduced Intramolecular Electron Transfer and Electronic Coupling Interactions in π- Expanded Imidazole Derivatives

An intramolecular excited charge transfer (CT) analysis of imidazole derivatives has been made. The determined electronic transition dipole moments has been used to estimate the electronic coupling interactions between the excited charge transfer singlet state (¹CT) and the ground state (S₀) or the locally excited state (¹LE). The properties of excited ¹CT state imidazole derivatives have been exploited by the significant contribution of the electronic coupling interactions. The excited state intramolecular proton transfer (ESIPT) analysis has also been discussed.     

壳模型对13N Gamow-Teller跃迁的研究

最近的研究表明¹³N的beta衰变对于Ia型超新星爆炸前的电子丰度有着重要的影响.本文在壳模型的基础上,首先计算¹³N基态到基态以及基态到不同激发态的Gamow-Teller(GT)跃迁强度,并将其与实验数据进行了比较.在理论计算的GT强度基础上,对不同温度和密度天体环境下¹³N的电子俘获率进行了细致的计算,并重点讨论基态到激发态的GT跃迁对电子俘获率变化的影响.结果表明,考虑基态到激发态的跃迁后,超新星的电子丰度下降,中微子能量损失增大.基态到激发态跃迁对电子俘获率的影响主要由低激发能级贡献. 关键词： Gamow-Teller跃迁 壳模型 电子俘获 激发态     

Vibronic problem in the higher excited states of F-center in alkali halides

Vibronic problem in the higher excited states of F-center in alkali halidesA new approach to the vibronic problems of bound polaron is proposed, taking advantage of the spherical symmetry of the system. By applying the obtained formula to the analysis of the transient absorption spectra due to the transition from the relaxed excited state to higher excited states of F-center in alkali halides, a good fit between the theory and the experiments is obtained and the final states of the transition are assigned to be 3p state and its phonon side bands perturbed through vibronic coupling.