Calculated Oscillator Strengths Research Articles

Enhanced oscillator strength of interband transitions in coupled Ge∕Si quantum dots

We report a calculation of oscillator strength for the Δ1−Γ25′ interband transition in two vertically coupled pyramidal Ge quantum dots embedded in Si. A six-band k⋅p formalism was used to study the Γ25′ hole states, and a single-band approach was used to obtain the Δ1 electron state interacting with the hole. The elastic strain due to the lattice mismatch between Ge and Si was included into the problem via the Bir–Pikus Hamiltonian. We find that when two dots are brought closely together, the oscillator strength may enlarge by a factor of about 2 as compared to the single-dot system.

Theoretical calculations of transition probabilities and oscillator strengths for Ti III and Ti IV

AbstractDue to the complicated electronic configuration of atoms and ions of the transition metal elements, the studies for properties such as transition probabilities and oscillator strengths for these atoms and ions are not systematic. Because of the existence in a variety of stellar objects and wide use in the field of astrophysics, titanium has long been of interest for many researchers. In this article within the Weakest Bound Electron Potential Model (WBEPM) theory, comprehensive set of calculations for transition probabilities and oscillator strengths for Ti III and Ti IV are performed. Many of our results had no previous experimental or theoretical values, so these predictive results could be of some value to the workers in this field. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Theoretical study of the discrete and continuum spectrum of BeH

The transition intensities supplied in this Letter are directly connected with a description of the discrete and continuum spectrum of BeH. An attempt to meet our goal requires the calculation of the absorption oscillator strengths of several transitions to Rydberg states of BeH, together with differential oscillator strengths which give rise to different dipole-allowed photoionization channels from the molecular ground state. The calculations have been performed with the molecular-adapted quantum defect orbital (MQDO) approach. Predictions of new spectroscopic data on BeH at energies where high Rydberg transitions can take place, including the continuum region of the spectrum have been made for the first time.

CHARGE TRANSFER COMPLEXES BETWEEN SOME CRYPTANDSWITH TETRACYANOETHYLENE AND 2- HYDROXY-1,4-NAPTHOQUINONE

The intermolecular charge transfer ( CT ) complex of two cryptands , viz , K221 and K222 (as donors ) and tow acceptors, viz , tetracyanoethylene (TCNE) and 2-hydroxy-1,4-napthoquinon were studied ion Uv-visible region in dichloromethane (DCM)as solvent at 298.2k .It was found that the basicity of cryptand played an important role in the formation constant Kc value obtained . The nature of CT complexes formed were achieved by calculation of oscillator strength .

Conjugated Oligomers and Polymers of cis- and trans-Platinum(II)-para- and ortho-bis(ethynylbenzene)quinone Diimine

Three conjugated polymers of the type (−spacer−C≡C−PtL2−C≡C−)n, with spacer = para- and ortho-bis(diphenyl(tetramethoxy)quinone diimine) and L = PEt3, were synthesized as the cis- and trans-isomers about the Pt. The three combinations (spacer/PtL2Cl2), ortho/trans, para/trans, and para/cis led to polydispersed polymers, which upon fractionation provided more monodispersed materials with Mn ranging from 3600 to 32400 (GPC). The spacer ortho-bis(diphenylethynyl)tetramethoxyquinone diimine reacts with cis-PtL2Cl2 to form small oligomers and a chelate cyclic complex (7), which was used as a model compound. All materials along with the aryl−C≡C−PtL2− C≡C−aryl models (L = PEt3; aryl = C6H5, 2,4,6-C6H2Me3; 2,4,5-C6H2Me3) were studied by 1H and 31P NMR, IR, UV–vis, TGA, DSC, luminescence spectroscopy, photophysics, and cyclic voltammetry. The UV–vis spectra exhibit an intramolecular low-energy and low-intensity charge transfer band (CT) assigned to π(Ph−C≡C) (for organics) and π/dxy((Ph−C≡C)2Pt) (for organometallics) to the π*(quinone diimine), as demonstrated by comparison with a corresponding amine derivative (i.e., no CT band) and corroborated by DFT and TDDFT. The polymers and 7 are not luminescent at room temperature (solid and solution). However in 2MeTHF at 77 K, the polymers bearing the combination ortho/trans and para/cis as well as the model compound 7 exhibit higher energy phosphorescence (Tn → S0) originating from the ππ*/dxy((Ph−C≡C)2Pt) excited states. A correlation between the structural parameters (angle made by the PtP2(C≡C)2 vs the aryl planes, angle made by the aryl and the quinone diimine planes, molecular weight) with the calculated oscillator strength, absorptivities, and the observed position of the lowest energy absorption bands is demonstrated. Finally, upper energy delayed fluorescence (Sn → S0) was detected for the polymers and 7 at 77 K and was assigned to T1−T1 interactions via aggregation as its intensity varies with the concentration.

Low-Lying Rydberg States of HCl

Vertical excitation energies belonging to some different Rydberg series of hydrogen chloride have been determined with a coupled-cluster theoretical approach. These excitation energies have allowed us to calculate electric dipole transition intensities in HCl and allow additional assessment of the calculation approach presently used to provide an adequate description of the valence and Rydberg states of HCl. The molecular quantum defect orbital has been applied to the calculation of oscillator strengths. In particular, new insight is given on the assignment of states as the R1Pi, the 1Delta(4dpi and 5ppi), the 1Sigma+(4dpi), and the nddelta(1Pi, 1Phi) and 4f states.

Oscillator strengths and lifetimes in Ge XXI

We have calculated energy splittings of 53 fine-structure levels as well as oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the (1s22s22p6)3s2(1S), 3s3p(1,3Po), 3s3d(1,3D), 3s4s(1,3S), 3s4p(1,3Po), 3s4d(1,3D), 3s4f(1,3Fo), 3p2(1S,3P,1D), 3p3d(1,3Po,1,3Do,1,3Fo), 3p4s(1,3Po) and 3d2(1S,3P,1D,3F,1G) states of Ge XXI, using extensive configuration–interaction (CI) wavefunctions, obtained with the CIV3 computer code of Hibbert. The important relativistic effects in intermediate coupling are incorporated by means of the Breit–Pauli Hamiltonian. In order to keep our calculated energy splittings as close as possible to the experimental values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. Our excitation energies, including their ordering, are in excellent agreement with the available experimental results. The enormous mixing among several fine-structure levels makes it very difficult to identify them correctly with the result that their positions in the calculation of Ivanova et al are interchanged compared to our results and the experimental values. From our transition probabilities, we have also calculated radiative lifetimes of some fine-structure levels. Our calculated oscillator strengths and the lifetimes are found to be in good agreement with the other available theoretical results. In this calculation, we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.

Laser-induced-fluorescence lifetime measurements and relativistic Hartree-Fock oscillator strength calculations in singly ionized platinum

Radiative lifetimes of eight odd-parity states of Pt II, in the energy range from 51 408 to $64\text{ }388\text{ }{\text{cm}}^{\ensuremath{-}1}$, have been measured by means of the time-resolved laser-induced-fluorescence technique. Free, singly ionized platinum ions were obtained in a laser-produced plasma and a tunable laser with 1.5 ns duration pulse was used to selectively excite the ${\text{Pt}}^{+}$ ions. The comparison of the experimental results with relativistic Hartree-Fock calculations emphasizes the importance of valence-valence correlation and of core-polarization effects in this complex ion. A new and extensive set of calculated oscillator strengths and transition probabilities is reported in the present paper.

Electric quadrupole oscillator strengths of helium

AbstractUsing a set of explicitly correlated trial wave functions that describe the three lowest singlet and triplet states of the helium atom with symmetry S, P, and D, we calculate the electric quadrupole oscillator strengths for all possible 1S‐1D, 1P‐1P, 1D‐1D, 3S‐3D, 3P‐3P, and 3D‐3D transitions and compare their accuracy to our earlier calculations of the electric dipole oscillator strengths. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

VUV absorption spectroscopy of acetonitrile between 7 and 20 eV: A revisionist study

The VUV absorption spectrum of acetonitrile between 7 and 20 eV was obtained at high resolution using monochromatised Kr lamp radiation and synchrotron radiation as photon excitation sources. Absorption cross sections were measured over the spectral range studied. We have reinterpreted or assigned for the first time the bands of four valence transitions in the 7–12 eV region, aided by M.O. calculations of transition energies and oscillator strengths. These assignments also required consideration of vibronic symmetry conditions in electronic transitions not previously discussed in the context of the interpretation of acetonitrile VUV absorption spectra. Considerable revision of previously assigned Rydberg transitions converging to the ground 1 2E and first excited 1 2A 1 states of the cation in the 8.9–13.2 eV region was also effected. The vibrational modes and frequencies in the valence and Rydberg states and their relation to bonding characteristics of the molecular orbitals are discussed in detail. Absorption features in the 14.2–15.4 eV higher energy region, probably involve Rydberg transitions converging to the 2 2E ion state at 15.133 eV.

Electronic Absorption Spectra of Praseodymium in Molten Chlorides

Electronic absorption spectra of trivalent praseodymium in various alkali chloride melts were precisely measured. The oscillator strength of the hypersensitive transition, 3F2 ←3H4, showed a clear decrease with increasing temperature. This temperature dependence was the inverse of reported cases for other trivalent lanthanoides. The Judd-Ofelt parameter was analysed, and the calculated oscillator strength showed quite good agreement with the experimentally obtained oscillator strength. However, the Ω2 parameter, which is sensitive to the ligand environment change, showed a clear decrease with increasing temperature and negative values at high temperature. We found that the 3P0 ←3H4 transition and its shoulder peak are quite sensitive to the coordination circumstance change of the [PrCl6]3− complex in molten chlorides. These intensities could be correlated with the octahedral symmetry of [PrCl6]3−.

First-principles calculation of the zone center phonons inZnSiN2: Comparison with infrared data

First-principles calculations were performed for the structure and zone center phonons in $\mathrm{Zn}\mathrm{Si}{\mathrm{N}}_{2}$ using the pseudopotential linear-response approach in the generalized gradient approximation. The lattice constants are obtained in agreement with experiment to better than 1%. The static and high-frequency dielectric constants in the $a$, $b$, and $c$ directions are obtained to be about 9.3, 9.9, and 11.0 and 4.9, 4.9, and 5.4, respectively. Using the calculated oscillator strengths and high-frequency dielectric tensor, the infrared spectrum for the ${b}_{1}$ modes is obtained in excellent agreement with experimental data both in terms of peak positions (to within a few percent) and relative peak heights. Our calculations show, however, that the broad higher-frequency peaks in the experiment are still superpositions of unresolved modes. A low-frequency mode at $277\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ with strong oscillator strength predicted by our calculations has thus far not been detected experimentally. This may be due to a short lifetime owing to phonon-phonon scattering to modes at other points in the Brillouin zone, as evidenced by a high density of states near this frequency. Predictions are made for the phonon spectra of other infrared active symmetry modes. Significant anisotropy of the infrared response is obtained. The mode Gr\"uneisen parameters are calculated and various sum rules related to the LO-TO splittings and the Born effective charges are checked.

Nonadiabatic couplings from time-dependent density functional theory: Formulation in the Casida formalism and practical scheme within modified linear response

We present an efficient method to compute nonadiabatic couplings (NACs) between the electronically ground and excited states of molecules, within the framework of time-dependent density functional theory (TDDFT) in frequency domain. Based on the comparison of dynamic polarizability formulated both in the many-body wave function form and the Casida formalism, a rigorous expression is established for NACs, which is similar to the calculation of oscillator strength in the Casida formalism. The adiabatic local density approximation (ALDA) gives results in reasonable accuracy as long as the conical intersection (ci) is not approached too closely, while its performance quickly degrades near the ci point. This behavior is consistent with the real-time TDDFT calculation. Through the use of modified linear response theory together with the ground-state-component separation scheme, the performance of ALDA can be greatly improved, not only in the vicinity of ci but also for Rydberg transitions and charge-transfer excitations. Several calculation examples, including the quantization of NACs from the Jahn-Teller effect in the H3 system, have been given to show that TDDFT can efficiently give NACs with an accuracy comparable to that of wave-function-based methods.

Relativistic Configuration Interaction Treatment ofGeneralized Oscillator Strength for Krypton

A fully relativistic configuration interaction method is developed toinvestigate the transition energies and general oscillator strengths ofthe lower lying states of krypton, for both optically allowed andoptically forbidden transitions. The calculated results are inagreement with the recent experimental measurements. The calculatedtransition energies for the 5s and 5s′ transitions are9.970 and 10.717 eV, which agree with the experimental data of 10.033and 10.643 eV. The calculated oscillator strengths are 0.211 and 0.170,comparable with the experimental results 0.214(±0.012) and 0.194(±0.012), respectively. The momentum transfer positions (K2 ina.u.) of the minimum and maximum GOSs in the 4s24p6→4s24p5 (5s+5s′) transitions are 1.105 and 2.225, comparable with themeasurements results 1.24 and 2.97 [Phys. Rev. A 67 (2003) 062708].

Oscillator strengths of allowed and intercombination lines in Si II using non-orthogonal wavefunctions

The importance of valence–shell, core–valence and core–core correlation and interactions between the members of 3s2nd 2D Rydberg series and between the Rydberg series and 3s3p22D perturber state in singly ionized silicon has been examined using term-dependent non-orthogonal orbitals in the multiconfiguration Hartree–Fock approach. Large sets of spectroscopic and correlation non-orthogonal functions have been chosen to adequately describe the term dependence of wavefunctions, various correlation corrections and strong interactions in Rydberg series. The relativistic corrections are included through the one-body mass correction, Darwin and spin–orbit operators and two-body spin–other-orbit operator in the Breit–Pauli Hamiltonian. Extensive configuration-interaction wavefunctions have been used in the representation of Si II levels to calculate oscillator strengths and transition probabilities. The accuracy of present oscillator strengths is evaluated by the agreement between the length and velocity formulations combined with the agreement between the calculated and measured transition energies. The present results have been compared with previous calculations, experimental measurements and astronomical observations.

Spectral properties of In II from MCDHF calculations

We report extensive relativistic multiconfiguration Dirac–Hartree–Fock calculations of oscillator strengths and hyperfine structures for a large number of electric dipole transitions in In II. Results for the 5s21S0–5s5p3Po0 hyperfine induced transition are also presented. Core polarization is accounted for by means of explicit CI. To describe spin–polarization effects configuration state functions obtained by single excitations from all core-shells are included in the expansions. The computed oscillator strength for the 5s21S0–5s5p3Po1 intercombination transition is in good agreement with laser spectroscopy measurements of In+ ions in a radio-frequency trap. The calculated magnetic dipole hyperfine interaction constants agree very well with experimental constants derived from Fourier transform spectra. The problem with off-diagonal interactions affecting the hyperfine structures in closely spaced fine-structure levels is discussed.

Breit–Pauli energy levels belonging to 2p 4, 2s2p 5, 2p 6, 2p 33ℓ configurations and all E1 transitions among these levels in Mg V

We present accurate oscillator strengths, line strengths and radiative rates for 1073 E1 transitions among the 86 levels belonging to 2s 22p 4, 2s2p 5, 2p 6, and 2s 22p 3( 4S o, 2D o, 2P o)3ℓ configurations in Mg V. We have used 1s and 2s Hartree–Fock orbitals, re-optimized 2p on 2p 3( 2D o)3s 3D o and optimized 3s,3p,3d orbitals on real states. Sixteen additional orbitals up to 8d are optimized either as a correction to n = 3 physical orbitals or as a correlation orbital. A very large set of configurations including up to three electron promotions are used to account for all important correlation effects. All of the main five terms in the Breit–Pauli operator (except the orbit–orbit interaction) are included in order to account for the relativistic effects. Small adjustments to the diagonal elements of the Hamiltonian matrix are made to bring the calculated energies within a few cm −1 of the corresponding NIST recommended data wherever available. The calculated oscillator strengths, line strengths, and radiative rates for almost all of the E1 transitions show excellent agreement with the corresponding MCDF results of Fischer. The recent results of Bhatia et al. are found to be consistently higher by 20–45%. The accuracy of the present calculation is considered to be better than the NIST accuracy ratings for various transitions.

Absorption spectral studies of 4f–4f transitions for the complexation of Pr(III) and Nd(III) with glutathione reduced (GSH) in presence of Zn(II) in different aquated organic solvents and kinetics for the complexation of Pr(III):GSH with Zn(II)

Abstract Comparative absorption and spectral analysis of 4f–4f transitions of the heterobimetallic complexation of glutathione reduced (GSH) with Pr(III) and Nd(III) in presence of Zn(II) has been explored in different aquated organic solvents like methanol (CH 3 OH), acetonitrile (CH 3 CN), dioxane, DMF and their equimolar mixtures. The variation in the energy parameters like Slater Condon ( F K ), Racah ( E K ) and Lande ( ξ 4f ), Nephelauxetic parameter ( β ) bonding parameter ( b 1/2 ) and percent covalency parameter ( δ ) are computed to explain the nature of complexation. The values of experimentally calculated oscillator strengths ( P ) and computed values of Judd–Ofelt electric dipole intensity parameters, T λ ( λ = 2, 4, 6) are studied for different 4f–4f transitions in different experimental conditions. The changes in the values of oscillator strengths ( P ) and T λ parameters also suggest the specific correlation between relative intensities, ligand structures and nature of interaction of Pr(III) and Nd(III) with GSH in presence of Zn(II). Kinetics for the formation of the complex, Pr(III):GSH:Zn(II) have also been studied at different temperatures in DMF medium and activation energy ( E a ) of the complexation is calculated.

Relativistic many-body calculations of electric-dipole lifetimes, rates and oscillator strengths of Δn = 0 transitions between 3l−14l′ states in Ni-like ions

Transition rates, oscillator strengths and line strengths are calculated for electric-dipole (E1) transitions between odd-parity 3s23p63d94l1, 3s23p53d104l2 and 3s3p63d104l1 states and even-parity 3s23p63d94l2, 3s23p53d104l1 and 3s3p63d104l2 (with 4l1 = 4p, 4f and 4l2 = 4s, 4d) in Ni-like ions with the nuclear charges ranging from Z = 34 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s22s22p63s23p63d10 Dirac–Fock potential. First-order RMBPT is used to obtain intermediate coupling coefficients and second-order RMBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E1 matrix elements to ensure the gauge independence of transition amplitudes. Transition energies used in the calculation of oscillator strengths and transition rates are from second-order RMBPT. Lifetimes of the 3s23p63d94d levels are given for Z = 34–100. These atomic data are important in modelling of M-shell radiation spectra of heavy ions generated in electron beam ion trap experiments and in M-shell diagnostics of plasmas.

Finite-temperature random-phase approximation for spectroscopic properties of neon plasmas

A finite-temperature random-phase approximation (FTRPA) is applied to calculate oscillator strengths for excitations in hot and dense plasmas. Application of the FTRPA provides a convenient, self-consistent method with which to explore coupled-channel effects of excited electrons in a dense plasma. We present FTRPA calculations that include coupled-channel effects. The inclusion of these effects is shown to cause significant differences in the oscillator strength for a prototypical case of $^{1}P$ excitation in neon when compared with single-channel and with average-atom calculations. Trends as a function of temperature and density are also discussed.