Dipole Oscillator Strengths Research Articles

Transition energy and oscillator strength of Sc 18+ ion

The transition energies and the dipole oscillator strengths for the 1s22s–1s2np (2 ≤n≤ 9) and 1s22p–1s2nd (3 ≤n≤ 9) of lithium-like Sc18+ ion are calculated by using the full core plus correlation method. The fine structure splittings of 1s2np and 1s2nd (n≤ 9) states are determined from the expectation values of spin-orbit and spin-other-orbit interaction operators. The quantum defects of these series, as function of principal quantum number n, are obtained. The agreement between the f-values obtained from three alternative formulae is excellent. Comparisons of our results with experimental data available in the literature are carried out. Combining the single-channel quantum defect theory with the discrete oscillator strengths obtained in this work, this paper obtains the behaviour of discrete oscillator strengths and oscillator strength densities corresponding to the bound-free transitions adjacent to ionization threshold.

Energy Ranking of Molecular Crystals Using Density Functional Theory Calculations and an Empirical van der Waals Correction

By combination of high level density functional theory (DFT) calculations with an empirical van der Waals correction, a hybrid method has been designed and parametrized that provides unprecedented accuracy for the structure optimization and the energy ranking of molecular crystals. All DFT calculations are carried out using the VASP program. The van der Waals correction is expressed as the sum over atom-atom pair potentials with each pair potential for two atoms A and B being the product of an asymptotic C(6,A,B)/r(6) term and a damping function d(A,B)(r). Empirical parameters are provided for the elements H, C, N, O, F, Cl, and S. Following Wu and Yang, the C(6) coefficients have been determined by least-squares fitting to molecular C(6) coefficients derived by Meath and co-workers from dipole oscillator strength distributions. The damping functions d(A,B)(r) guarantee the crossover from the asymptotic C(6,A,B)/r(6) behavior at large interatomic distances to a constant interaction energy at short distances. The careful parametrization of the damping functions is of crucial importance to obtain the correct balance between the DFT part of the lattice energy and the contribution from the empirical van der Waals correction. The damping functions have been adjusted to yield the best possible agreement between the unit cells of a set of experimental low temperature crystal structures and their counterparts obtained by lattice energy optimization using the hybrid method. On average, the experimental and the calculated unit cell lengths deviate by 1%. To assess the performance of the hybrid method with respect to the lattice energy ranking of molecular crystals, various crystal packings of ethane, ethylene, acetylene, methanol, acetic acid, and urea have been generated with Accelrys' Polymorph Predictor in a first step and optimized with the hybrid method in a second step. In five out of six cases, the experimentally observed low-temperature crystal structure corresponds to the most stable calculated structure.

Conversion efficiency of a laser-produced Sn plasma at 13.5 nm, simulated with a one-dimensional hydrodynamic model and treated as a multi-component blackbody

Efficiency optimization of a stable and debris free plasma source at 13.5 nm, is at the forefront of current extreme ultraviolet lithographic (EUVL) research efforts. To date, 1–2.5% soft x-ray conversion efficiencies (CEs) within a 2% bandwidth (BW) around 13.5 nm and into 2π steradians have been attained experimentally for laser-produced plasmas containing Sn at power densities of 0.5–5 × 1011 W cm−2. In order to complement these experimental endeavours, we have undertaken to study the CE, for the given wavelength regime, in the optically thick limit. We have achieved this by coupling time-dependent and steady-state collisional-radiative (CR) equations to the output of the one-dimensional hydrodynamic code MED103 (MEDUSA), where a solid sphere of radius 50 µm was uniformly irradiated by a high intensity laser pulse with a Gaussian temporal profile. The ion populations obtained from these CR results were then used in an integrated spatio-temporal figure of merit (FOM) together with in-band weighted dipole oscillator strengths and transition energies. The maximum FOM, when divided by the laser energy, was found to occur in the range of peak power densities of 2–3 × 1011 W cm−2 for the steady-state and time-dependent models, respectively. The hydrodynamic variables of these peak power densities were then used in a radiative transfer calculation in which the many-celled spherical plasma was treated as a multi-component blackbody. It is found that CEs of 3.5–6% within the 2% BW per 2π steradians may be achieved. These results are of particular relevance to EUVL technologies where a minimum CE of 3% is required by industry.

Electronic structure of the calcium monohydroxide radical

Effective valence shell Hamiltonian H(v) calculations are used to map out three-dimensional potential energy surfaces for the 12 lowest electronic states of the CaOH radical. Excitation energies and spectroscopic constants are compared with experiment and prior computations where available, but many previously unavailable data are provided, including excited state dipole moments and oscillator strengths. Particular attention is paid to clarify the nature of nonlinear and quasilinear excited states, Renner-Teller couplings, and state mixings. The F (2)Pi and G (2)Pi (6 (2)A(') and 8 (2)A(')) states are both found to possess nonlinear local minima, due to an avoided crossing. Attention is also focused on the characteristics of basis sets necessary in high-accuracy calculations for the CaOH radical.

Dipole Oscillator Strength Distributions and Properties for Methanol, Ethanol and Propan-1-ol and Related Dispersion Energies

Recommended isotropic dipole oscillator strength distributions (DOSDs) have been constructed for the methanol and ethanol molecules through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength (DOS) data; the DOS data employed are recent experimental results not available at the time of the original constrained DOSD analysis of these molecules. The constraints are furnished by molar refractivity data and the Thomas-Reiche-Kuhn sum rule. The DOSDs are used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums, and mean excitation energies for the molecules. Pseudo-DOSDs for these molecules, and for propan-1-ol based on an earlier constrained DOSD analysis for this molecule, are also presented. They are used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interactions of the alcohols with each other and with 36 other species, and the triple-dipole dispersion energy coefficients C9for interactions involving any triple of molecules involving methanol, ethanol and propan-1-ol.

Reliable results for the Isotropic Dipole – Dipole and Triple – Dipole Dispersion Energy Coefficients for Interactions involving Formaldehyde, Acetaldehyde, Acetone, and Mono - , Di - , and Tri - Methylamine

Pseudo - spectral dipole oscillator strengths and excitation energies, which are discrete representations of previously developed recommended continuous dipole oscillator strength distributions(DOSDs), are presented for the ground state formaldehyde, acetaldehyde, acetone, and mono - , di - , and tri - methylamine molecules. These pseudo - DOSDs, together with previously published pseudo - DOSDs for other atoms and molecules, are used to evaluate the dipole - dipole and the triple - dipole dispersion energy coefficients for all the two - body and three - body interactions between H$_2$CO, CH$_3$CHO, (CH$_3$)$_2$CO, CH$_3$NH$_2$, (CH$_3$)$_2$ NH, and (CH$_3$)$_3$N, and between these molecules and forty - four other species, namely Cl$_2$, SiH$_4$, SiF$_4$, CCl$_4$, H, Li, He, Ne, Ar, Kr, Xe, SF6, HF, HCl, HBr, SO$_2$, CS$_2$, OCS, H$_2$, N$_2$, O$_2$, NO, N$_2$O, H$_2$O, H$_2$S, NH$_3$, CO, CO$_2$, the normal alkanes CH$_4$, C$_2$H$_6$, C$_3$H$_8$, C$_4$H$_{10}$, C$_5$H$_{12}$, C$_6$H$_{14}$, C$_7$H$_{16}$ and C$_8$H$_{18}$, the 1-alkenes C$_2$H$_4$, C$_3$H$_6$ and C$_4$H$_8$, C$_2$H$_2$, C$_6$H$_6$, and the primary alcohols CH$_3$OH, C$_2$H$_5$OH and C$_3$H$_7$OH. Results are presented explicitly for all the dipole - dipole dispersion energy coefficients and for the triple - dipole coefficients for all three -body interactions involving the H$_2$CO, CH$_3$CHO, (CH$_3$)$_2$CO, CH$_3$NH$_2$, (CH$_3$)$_2$ NH, and (CH$_3$)$_3$N molecules. The estimated errors in the two - body and three - coefficients are 1% and 1-2%

New approximations for calculating dispersion coefficients.

Improved approaches for finding approximate values of dispersion coefficients are proposed. They are based on scaling the values of time-dependent Hartree-Fock (TDHF) dispersion coefficients by factors that use the ratio of the estimated true value and the TDHF value of static dipole polarizabilities. It is shown that for a set of 14 atoms and molecules the average absolute-value deviation of the estimated two-body isotropic dispersion coefficients with respect to the dipole oscillator strength distribution results is smaller than 1.0% for two of our approaches. For three-body isotropic dispersion coefficients the corresponding deviations are smaller than 1.2%. Our approximations work particularly well compared to approximations proposed by other researchers in cases where the TDHF results differ from the reference values by more than 10%.

Inner-shell photoexcitation of Fe xv and Fe xvi

The configuration-interaction method as implemented in the computer code CIV3 is used to determine energy levels, electric dipole radiative transition wavelengths, oscillator strengths and transition probabilities for inner-shell excitation of transitions in Fe XV and Fe XVI. Specif

Dipole oscillator strengths, dipole properties and dispersion energies for SiF4

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the silicon tetrafluoride (SiF4) molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength data. The constraints are furnished by experimental molar refractivity data and the Thomas-Reiche-Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums and mean excitation energies for the molecule. A pseudo-DOSD for SiF4 is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interaction of SiF4 with itself and with 43 other species and the triple-dipole dispersion energy coefficient C9 for (SiF4)3.

Sodium in a strong magnetic field

We investigate the effects of a magnetic field with low to intermediate strength on several spectroscopic properties of the sodium atom. A model potential is used to describe the core of sodium, reducing the study of the system to an effective one-particle problem. All states with principal quantum numbers n = 3, 4, 5, 6 and 7 are studied and analysed. A grid of twenty values for the field strength in the complete regime B = 0 - 0.02 a.u. is employed. Ionisation energies, transition wavelengths and their dipole oscillator strengths are presented.

Relativistic configuration interaction calculations on the Kα x-raysatellites of argon

Relativistic configuration interaction calculations with the inclusion of Breitinteraction, quantum electrodynamics and finite nuclear mass corrections havebeen carried out in the extended optimal level scheme using multi-configurationDirac–Fock wavefunctions on the energy levels, electric dipole transition rates,oscillator strengths and radiative lifetimes of argon with a single vacancy in the Kshell, varying degrees of ionization in the L shell and open outer shells. Thecalculations have been carried out in both the Babushkin and Coulombgauges to check the sensitivity of the orbital functions employed in theevaluation of transition rates. The calculated energies and transition rates arecompared with available experimental data and other theoretical calculations.

RELATIVISTIC DISTORTED-WAVE COLLISION STRENGTHS AND OSCILLATOR STRENGTHS FOR THE 45Δ n=0 TRANSITIONS WITH n=2 IN THE 79 O-LIKE IONS WITH 14≤ Z≤92

Relativistic distorted-wave collision strengths have been calculated for the 45 Δ n=0 transitions with n=2 in the 79 O-like ions with nuclear charge number Z in the range 14≤ Z≤92. The calculations were made for the six final, or scattered, electron energies E′=0.03, 0.08, 0.20, 0.42, 0.80, and 1.40, where E′ is in units of Z 2 eff Ry with Z eff= Z−5.83. In addition, the transition energies and electric dipole oscillator strengths are given. To our knowledge the present work is the first comprehensive publication of the results of fully relativistic calculations of the collision strengths for excitation of highly charged O-like ions.

Dipole oscillator strength properties and dispersion energies for SiH4

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the silane (SiH4) molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength data. The constraints are furnished by experimental molar refractivity data and the Thomas–Reiche–Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums, and mean excitation energies for the molecule. A pseudo-DOSD for SiH4 is also presented which is used to obtain reliable results for the isotropic dipole–dipole dispersion energy coefficients C6, for the interaction of silane with itself and with forty-four other species, and the triple–dipole dispersion energy coefficient C9 for ðSiH4Þ 3 . 2002 Elsevier Science B.V. All rights reserved.

Dipole oscillator strength properties and dispersion energies for CI2

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the chlorine molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength and molar refractivity data. It has been used to evaluate a variety of dipole oscillator strength sums, logarithmic dipole oscillator strength sums, and mean excitation energies for the molecule. A pseudo-DOSD for C12 is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interaction of Cl2 with itself and forty-two other species, and the triple-dipole dispersion energy coefficient C9 for (Cl2)3.

Effect of Debye plasma on the structural properties of compressed positronium atom

The effect of weakly coupled plasma on the energy levels and other structural properties of compressed positronium atom has been analysed. The positronium atom is treated as a quasistable system and the compression is obtained by embedding the atom at the centre of an impenetrable spherical box. The dipole polarizabilities, transition energies, oscillator strengths and transition probabilities of a few low lying allowed excited states have been obtained for various plasma strengths with different confinement radii.

Electronic excited states of conjugated cyclic ketones and thioketones: A theoretical study

Absorption spectra of a series of cyclic conjugated ketones and thioketones have been computed at the multiconfigurational second-order multistate perturbation level of theory, the CASSCF/MS-CASPT2 method. Excitation energies, transition dipole moments, oscillator strengths, and static dipole moments are reported and discussed for excited states with energies lower than ≈7–8 eV. The main bands of the spectra have been assigned and characterized in most cases for the first time. The spectroscopy of the different systems is compared in detail. Thioketones in particular have low-energy and intense ππ* transitions which suggest corresponding enhanced nonlinear molecular optical properties. Additionally, some of the methods used to estimate these properties from spectroscopic data have been considered in order to analyze the main contributions to the nonlinear optical properties.

On the oscillator strength sums S(±1) of atoms and ions

Using rigorous relations discovered recently, the Hartree–Fock limit values of the dipole oscillator strength sums S(−1) and S(+1) are obtained for the 102 neutral atoms He through Lr, singly charged 53 cations Li+ through Cs+, and 43 stable anions H− through I− in their experimental ground states. The present results for the ionic species are the first compilation of the sums. For heavy neutral atoms, the literature S(+1) values are found to be insufficiently accurate.

Reliable isotropic dipole properties and dispersion energy coefficients for CCl 4

Dipole oscillator strength distributions (DOSD) have been constructed for ground state CCl 4 molecule, by using constrained least-squares methods, experimental and mixture rule dipole oscillator strength data, and refractive index measurements. A recommended isotropic DOSD is used to evaluate a wide variety of dipole oscillator strength sums S K , logarithmic dipole sums L K and mean excitation energies I K . Pseudo-DOSDs have been constructed for CCl 4 molecule and these are used to calculate isotropic dipole–dipole dispersion energy coefficients C 6 for the interaction of CCl 4 with itself and with 45 other species, and the triple-dipole dispersion energy coefficients C 9 for (CCl 4) 3.

NIR to UV absorption spectra and the optical constants of phthalocyanines in glassy medium

Optical absorption studies of phthalocyanines (Pc-s) in borate glass matrix have been reported for the first time. Measurements have been done corresponding to photon energies between 1.1 and 6.2 eV for free base, manganese, iron, nickel, molybdenum, cobalt and copper phthalocyanines. Several new discrete transitions are observed in the UV–vis region of the spectra in addition to a strong continuum component of absorption in the IR region. Values of some of the important optical constants viz. absorption coefficient ( α), molar extinction coefficient ( ε), absorption cross-section ( σ a), band width (Δ λ), electric dipole strength ( q 2) and oscillator strength ( f) for the relevant electronic transitions are also presented. All the data reported for Pc-s in the new matrix have been compared with those corresponding to solution, vapor and thin film media.

Ionization and excitation yields in liquid water due to the primary irradiation: Relationship of radiolysis with far UV-photolysisPresented at the Symposium on Recent Trends in Photochemical Sciences, Trivandrum, January 8-10, 2000.

First collision yields of ionization and dissociation in liquid water, due to incident electrons of energy 500 eV to 1 MeV, have been calculated in the optical approximation by using the experimental dipole oscillator strength distribution (DOSD) and the recently determined photoionization and photodissociation quantum efficiencies in the far UV. From these the G value of ionization for the complete absorption of these radiations is estimated employing a heuristic method based on energy balance. It is found that ca. 25% of total ionization and <5% of total dissociation originate from primary interactions alone; the rest are due to the action of the secondary electrons. Incorporation of dissociative electron attachment (DEA) is necessary to account for the total radiolytic dissociation yield. A new definition of ionization potential in liquid water is provided depending on the mechanism and a tentative value of 11.7 eV is assigned to it.