Cleanthis A. Nicolaides

Oscillator strengths in first row neutral, singly and doubly ionized atoms: Comparison of recent theoretical and experimental values

Abstract Using correlated wave functions, oscillator strengths for transitions of the type 1s 2 2s 2 2p n → 1s 2 2s2p n +1 in neutral, singly and doubly ionized B, C, N, O and F atoms are calculated. Such oscillator strengths are extremely sensitive to the details of electronelectron interactions. Comparison with results for other many-body calculations and beam-foil, phase-shift, emission and Hanle spectroscopies shows an overall agreement in the case of ionized atoms but an occasional discrepancy in the case of the neutrals. It appears that, assuming experiment is correct, in these cases one still needs a better understanding of electron correlation and its effect on oscillator strengths.

Chemisorption and 1s binding energies in oxygen atom and negative ion

Abstract The use of accurate experimental 1s binding energies (B.E.) of an atom in its “free” and “adatom” states is proposed as a means of studying chemisorption forces. In the case of the oxygen atom, which is important for adsorption studies, there are no experimental results on the 1s binding energy of the free atom or negative ion. In this paper we report accurate, theoretical 1s B.E.s for O 3P and O−2P0 obtained using Sinanoglus non-closed shell many-electron theory (NCMET). We find: B.E. (O 3P) = 544.5 eV and B.E. (O−2P) = 528.6 eV. Hopefully these values will be useful for adsorption studies in the context of the approach outlined below.

Theory of non-stationary states in many-electron atoms

Abstract In this paper, a useful classification of atomic states into “stationary” and “non-stationary” states with further subdivisions with respect to the rate of de-excitation is provided. The stationary states are defined to be the well-known states observed by photon emission which have formed the basis for the conceptual development of Quantum Mechanics. The non-stationary states are defined to be those observed via electron emission and here I outline their proporties. I present a general approach which allows one to deal with them both conceptually and computationally. Certain similarities and differences from stationary states are pointed out. Inner-hole or doubly excited states, observed in various types experiments, are treated from a conceptually single point of view, as decaying states. The relevant important quantities are derived and interpreted in a mathematically and physically meaningful way. Accurate total energies are calculated by employing a variational minimum principlee which permits one to incorporate systematically the important correlation effects without the danger of a “variational collapse”. This method requires projection onto known, zeroth order functions and it thus overcomes the difficulties of the well-known P, Q methods which require projection onto exact wave functions. N-body calculations on three-electron atoms yield the He− 2s22p2p0 and 2s2p22D resonances, previously observed experimentally, at about 57.3 eV and 58.4 eV, as well as new resonances in Li I at about 141.7 eV (2s22p 2P0), 144.9 eV (2s2p22D) and 62.0 eV (1s2p22D), in B III at about 204.7 eV (1s2p22D) and in C IV at 306.7 eV (1s2p22D). These states, which are just samples of states treatable by this approach, may in principle cause observable structures, e.g., in photon-absorption, in particle-atom scattering or in beam-foil experiments.

Variational calculations of correlated wavefunctions and energies for ground, low-lying as well as highly excited discrete states in many-electron atoms using a new atomic structure theory including electron correlation

The authors have calculated to a high degree of accuracy correlated wavefunctions and their corresponding energies containing all the non-dynamical correlations of the non-closed shell many-electron theory by Sinanoglu and co-workers (1970). Ground as well as highly excited states of atoms and ions with three to nine electrons from beryllium to silicon are considered. Special care is applied to obtain wavefunctions of highly excited hole-states having lower states of the same symmetry, like Be I 1s2 2p2 1S, B I 1s2 2s 2p2 2S, O I 1s2 2s 2p5 3P0, F II 1s2 2s 2p5 1P0 and others. The methods, presented in reasonable detail, yield correlated wavefunctions accurate to approximately 0.001 au readily applicable to transition probabilities, hyperfine structure, spin-orbit coupling and other properties. Accurate wavelengths, term-splitting ratios and multiplet oscillator strengths for lines in highly ionized silicon, are given as an example of the applicability of the wavefunctions and energies obtained.

Theoretical lifetimes of the metastable 5S02 states in atomic carbon and oxygen

Abstract “We have performed many-electron calculation of the lifetimes (τ) of the metastable CI 1s 2 2s2p 3 5 S 0 2 “ and OI 1s 2 2s 2 2p 3 3s “ 5 S 0 2 ” states allowing for electron correlation and the full spin-orbit interaction. These calculations, the first of their kind, yield τ oxygen = 192 × 10 −6 sec and τ carbon = 176 × 10 −3 sec. The oxygen result is in excellent agreement with the very recent and only experimental value by Johnson of τ oxygen = (185 + − 10) × 10 −6 sec.

A proposed correction to the solar abundances of carbon and oxygen utilizing new and accurate theoretical forbidden transition probabilities

Previously published solar abundances of oxygen and carbon can be corrected to be logN(O) = 8.93 and logN(C) = 8.60 on the hydrogen log-scale when new accurate forbidden electric quadrupole transition probabilities AQ(s−1) are used. Such AQs, based on the new atomic structure and electron correlation theory, developed recently by Sinanoğlu and coworkers, are reported for the (1S0-1D2) lines of [C i], [N ii, [O i] and [O iii] and the (2P-2D) lines of [N i] and [O ii]. The available experimental values are also given for comparison.

Transition probabilities: New theory vs recent experimental results

Abstract Transition probabilities are calculated for various 1s22s22pn−1s22s2pn+1 electric dipole transitions in the first row ions C II, N I, N II, N III, O II, O III, O IV, F II, Ne II. A Non-Closed Shell Many Electron Theory (N.C.M.E.T.) of atomic structure developed by Sinanoǧlu and co-workers, which treats electron correlation accurately in both ground and excited states, predicts novel correlation effects which are included in the wave functions used to calculate the multiplet oscillator strengths. The calculated values are in agreement with recent experimental results within 10%. It is found that the usual improvement of the Hartree-Fock wave-function by the inclusion of a few configurations traditionally thought to be important, is not sufficient to obtain agreement with experiment. It is concluded therefore that all novel correlation effects as analyzed within the framework of N.C.M.E.T. should be included in the wave function to obtain accurate oscillator strengths.