The thermal decompositions of methyl azidoformate (N3COOMe), ethyl azidoformate (N3COOEt) and 2-azido-N,N-dimethylacetamide (N3CH2CONMe2) have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N2 appears as an initial pyrolysis product in all systems, and the principal interest lies in the fate of the accompanying organic fragment. For methyl azidoformate, four accompanying products were observed: HNCO, H2CO, CH2NH and CO2, and these are believed to arise as a result of two competing decomposition routes of a four-membered cyclic intermediate. Ethyl azidoformate pyrolysis yields four corresponding products: HNCO, MeCHO, MeCHNH and CO2, together with the five-membered-ring compound 2-oxazolidone. In contrast, the initial pyrolysis of 2-azido-N,N-dimethyl acetamide, yields the novel imine intermediate Me2NCOCHNH, which subsequently decomposes into dimethyl formamide (HCONMe2), CO, Me2NH and HCN. This intermediate was detected by matrix isolation IR spectroscopy, and its identity confirmed both by a molecular orbital calculation of its IR spectrum, and by the temperature dependence and distribution of products in the PES and IR studies. Mechanisms are proposed for the formation and decomposition of all the products observed in these three systems, based on the experimental evidence and the results of supporting molecular orbital calculations.
The QED contribution to the energies of the circular (n, = n–1), 2n13, transitions have been calculated for several kaonic atoms throughout the periodic table, using the current world-average kaon mass. Calculations were done in the framework of the Klein-Gordon equation, with finite nuclear size, finite particle size, and all-order Uelhing vacuum polarization corrections, as well as Källén and Sabry and Wichmann and Kroll corrections. These energy level values are compared with other computed values. The circular transition energies are compared with available measured and theoretical transition energies. Electron screening is evaluated using a Dirac-Fock model for the electronic part of the wave function. The effect of electronic wave-function correlation is evaluated.
In the present work we have calculated several relativistic transition probabilities for the F-like ions with 10 less-than-or-equals, slant Z less-than-or-equals, slant 49, in the framework of the Multi-Configuration Dirac–Fock method, for applications on laserphysics and astrophysics. The lines considered correspond to transitions between levels of 2p43s, 2p43p and 2p43d configurations. The spectral fine structure is taken into consideration and the results for individual lines are given.
Energies of the circular (n, ℓ = n − 1) 1 less-than-or-equals, slant n less-than-or-equals, slant 20 levels have been calculated for hydrogenlike sigmonic atoms with 1 less-than-or-equals, slant Z less-than-or-equals, slant 92, using the current world average sigma mass, as well as the electronic shift in Σ− + Ne e− + nucleus systems, where Ne stands for the number of electrons. The electronic influence on sigmonic orbitals has also been investigated through the computation of the hyperfine structure and the anomalous Σ− magnetic moment effects in sigmonic Be 2p states.
Energies and transition probabilities of Kβ hypersatellite lines are computed using the Dirac–Fock model for several values of Z throughout the periodic table. The influence of the Breit interaction on the energy shifts from the corresponding diagram lines and on the Kβh1/Kβh3 intensity ratio is evaluated. The widths of the double-K hole levels are calculated for Al and Sc. The results are compared to experiment and to other theoretical calculations.
Total electronic correlation corrections to the binding energies of the isoelectronic series of beryllium, neon, magnesium and argon, are calculated in the framework of relativistic multiconfiguration Dirac-Fock method. Convergence of the correlation energies is studied as the active set of orbitals is increased. The Breit interaction is treated fully self-consistently. The final results can be used in the accurately determination of atomic masses from highly charged ions data obtained in Penning-trap experiments.
Abstract. Total ionization cross sections of neutral phosphorus, arsenic, antimony, and bismuth atoms by electron impact are reported and compared to the only available experimental results by Freund et al. [Phys. Rev. A 41, 3575 (1990)]. These calculations take into account the possibilities that some target atoms used in the experiments were in metastable states close to the ground state, the excitation-autoionization of nsnp4 excited states may be substantial, and the ions produced in experiments may be in excited, low-lying metastable states. The cross sections for direct ionization calculations are based on the BEB model by Kim and Rudd [Phys. Rev. A 50, 3954 (1994)]. Plane-wave Born cross sections scaled by the method developed by Kim [Phys. Rev. A 64, 3954 032713 (2001)] are used to determine the contributions from excitation-autoionization. The combination of the BEB model and the scaled Born cross sections is in agreement with the experimental data by Freund et al. These theoretical data are useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies.
Experimental relative transition probabilities for the 16 more pro-eminent lines arising from the 6p configurations of Au II were determined from the emission-line intensities in a laser-produced plasma. The experiment was carried out using a Cu-Au alloy with 10% Au content in order to obtain an optically thin plasma. Transition probabilities were placed on an absolute scale by using theoretical lifetimes calculated in this work, line-strength sum rules and Boltzmann plot. A comparison has been conducted between present experimental results, the theoretical data available and new calculations with the multi-configuration Dirac-Fock method reported in this work, as well as a study of the plasma conditions.
In this paper we review the different relativistic and QED contributions to energies, ionic radii, transition probabilities and Landé g-factors in super-heavy elements, with the help of the MultiConfiguration Dirac-Fock method (MCDF). The effects of taking into account the Breit interaction to all orders by including it in the self-consistent field process are demonstrated. State of the art radiative corrections are included in the calculation and discussed. We also study the non-relativistic limit of MCDF calculation and find that the non-relativistic offset can be unexpectedly large.
The transition probabilities of Kα hypersatellite lines and energy shifts with respect to the corresponding diagram lines are computed using the Dirac–Fock model for several values of atomic number Z throughout the periodic table. The influence of the Breit interaction on the Kα1h/Kα2h line intensity ratio, Kα1h and Kα2h line energy shifts and Kα1h to Kα2h line energy splitting is evaluated. Double-K shell hole threshold values for selected elements with 23 ⩽Z⩽ 30, calculated within the same approach, are compared with available experimental results.
Ab initio and density functional calculations have been performed to study the benzyl azide, 2-, 3- and 4-methyl benzyl azides. Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionisation energies were also computed.
Wavelengths and oscillator strengths for all dipole-allowed fine-structure transitions in Zr III have been calculated within the Multi-Configuration Dirac-Fock method with QED corrections. These transitions are included in the spectrum of some chemically peculiar stars, like the B-type star Lupi observed by the Hubble space telescope. The results are compared to existing experimental and semi-empirical data.
A theoretical study of the all two-photon transitions from initial bound states with ni=2,3 in hydrogenic ions is presented. High-precision values of relativistic decay rates for ions with nuclear charge in the range 1<=Z<=92 are obtained through the use of finite basis sets for the Dirac equation constructed from B splines. We also report the spectral (energy) distributions of several resonant transitions, which exhibit interesting structures, such as zeros in the emission spectrum, indicating that two-photon emission is strongly suppressed at certain frequencies. We compare two different approaches (the line profile approach and the QED approach based on the analysis of the relativistic two-loop self-energy) to regularize the resonant contribution to the decay rate. Predictions for the pure two-photon contributions obtained in these approaches are found to be in good numerical agreement.
The theory of domain decomposition is described and used to divide the variable domain of a diatomic molecule into separate regions which are solved independently. This approach makes it possible to use fast Krylov methods in the broad interior of the region while using explicit methods such as Gaussian elimination on the boundaries. As is demonstrated by solving a number of model problems, these methods enable one to obtain solutions of the relevant partial differential equations and eigenvalue equations accurate to six significant figures with a small amount of computational time. Since the numerical approach described in this article decomposes the variable space into separate regions where the equations are solved independently, our approach is very well-suited to parallel computing and offers the long term possibility of studying complex molecules by dividing them into smaller fragments that are calculated separately.
We study the contribution of the most important processes leading to the creation of excited states of Cl14+ ions from the ground configurations of Cl ions in an Electron Cyclotron Resonance Ion Source (ECRIS), which lead to the emission of K X-ray lines. Theoretical values for inner-shell excitation, K and KL ionization cross-sections, and energies and transition probabilities for the de-excitation processes are calculated in the framework of the Multi-Configuration Dirac-Fock (MCDF) method. With reasonable assumptions about the electron energy distribution, a theoretical K[alpha] X-ray spectrum is obtained, which reproduces closely a recent experimental result.
We present a first theoretical determination of the hyperfine coupling constants of a spherical top molecule using ab initio methods. The scalar and tensorial contributions to the spin-rotation constants and the diamagnetic and paramagnetic contributions to the nuclear shielding constant are calculated for the 32SF6 molecule. The corrections to the spin-rotation constants due to nuclear Thomas precession are evaluated and discussed. Our results are compared with previously reported experimental values.
The two-photon decay of heavy, helium-like ions is investigated based on second-order perturbation theory and Dirac’s relativistic equation. Special attention has been paid to the angular emission of the two photons (i.e., how the angular correlation function depends on the shell structure of the ions in their initial and final states). Moreover, the effects from the (electric and magnetic) nondipole terms in the expansion of the electron-photon interaction are discussed. Detailed calculations have been carried out for the two-photon decay of the 1s2s1S0, 1s2s3S1, and 1s2p3P0 states of helium-like Xe52+, Au77+, and U90+ ions.
There is a need for reliable theoretical methods to calculate electron-impact total ionization cross sections for the large number of neutral atoms and ions with open shell structures. These cross sections are used in a wide range of scientific and industrial applications, such as astrophysical plasmas, atmospheric science, X-ray lasers, magnetic fusion, radiation physics, semiconductor fabrication, accelerator physics and tumor therapy physics. The binary-encounter-Bethe (BEB) model [1], using an analytic formula that requires only two atomic constants, the binding energy and kinetic energy of the electrons, generates direct ionization cross sections for any neutral atom (or molecule), which are reliable in intensity (15%) and shape from the ionization threshold to a few keV in the incident energy [3], or to thousands keV if we consider its relativistic version(RBEB) [2]. In this work we present K- and L-shell ionization cross sections calculations for heavy atoms.
Two-photon decay of hydrogenlike ions is studied within the framework of second-order perturbation theory, based on the relativistic Dirac's equation. Special attention is paid to the effects arising from the summation over the negative-energy (intermediate virtual) states that occur in such a framework. In order to investigate the role of these states, detailed calculations have been carried out for the 2s1/2–>1s1/2 and 2p1/2–>1s1/2 transitions in neutral hydrogen H as well as for hydrogenlike xenon Xe53+ and uranium U91+ ions. We found that for a correct evaluation of the total and energy-differential decay rates, summation over the negative-energy part of Dirac's spectrum should be properly taken into account both for high-Z and low-Z atomic systems.
The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K x-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double-KL and triple-KLL ionizations, transition probabilities and energies for the de-excitation processes, are calculated in the framework of the multiconfiguration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical Kalpha x-ray spectrum is obtained, which is compared to recent experimental data.
