Resonance structures in the multichannel quantum defect theory for the photofragmentation processes involving one closed and many open channels

The transformation introduced by Giusti-Suzor and Fano and extended by Lecomte and Ueda for the study of resonance structures in the multichannel quantum defect theory (MQDT) is used to reformulate MQDT into the forms having one-to-one correspondence with those in Fano's configuration mixing (CM) theory of resonance for the photofragmentation processes involving one closed and many open channels. The reformulation thus allows MQDT to have the full power of the CM theory, still keeping its own strengths such as the fundamental description of resonance phenomena without an assumption of the presence of a discrete state as in CM.Comment: 7 page

Stieltjes-moment-theory technique for calculating resonance width's

A recently developed method for calculating the widths of atomic and molecular resonances is reviewed. The method is based on the golden-rule definition of the resonance width, GAMMA(E). The method uses only square-integrable, L/sup 2/, basis functions to describe both the resonant and the non-resonant parts of the scattering wave function. It employs Stieltjes-moment-theory techniques to extract a continuous approximation for the width discrete representation of the background continuum. Its implementation requires only existing atomic and molecular structure codes. Many-electron effects, such as correlation and polarization, are easily incorporated into the calculation of the width via configuration interaction techniques. Once the width, GAMMA(E), has been determined, the energy shift can be computed by a straightforward evaluation of the required principal-value integral. The main disadvantage of the method is that it provides only the total width of a resonance which decays into more than one channel in a multichannel problem. A review of the various aspects of the theory is given first, and then representative results that have been obtained with this method for several atomic and molecular resonances are discussed. 28 references, 3 figures, 4 tables. (RWR

Even-parity quartet autodetaching states of He/sup -/

The total photodetachment cross section of the metastable, (1s2s2p) /sup 4/P/sup 0/ state of He/sup -/ has been recently measured at several wavelengths between 10 ..mu.. and 308 nm. As part of these calculations, the even parity, quartet, autodetaching states of He/sup -/ which are optically connected to the metastable /sup 4/P/sup 0/ state and which are associated with the n = 2 and n = 3 states of He were studied. In both the photodetachment and electron scattering calculations, extensive configuration interaction (CI) wavefunctions were used to describe the He target states, the He/sup -/ resonance states and the photodetachment continua. The Stieltjes moment-theory technique was used to extract the partial photodetachment cross sections from the discrete representations of the electron scattering continua. The use of the Stieltjes technique allowed the inclusion of both channel-channel coupling and fully correlated He /sup 3/S and /sup 3/P/sup 0/ wavefunctions in the calculations. Results are presented and discussed. (WHK

Theory and analysis of soft x-ray laser experiments

The atomic modeling of soft x-ray laser schemes presents a formidable challenge to the theorists - a challenge magnified by the recent successful experiments. A complex plasma environment with many ion species present must be simulated. Effects such as turbulence, time dependence, and radiation transport, which are very difficult to model accurately, may be important. We shall describe our efforts to model the recently demonstrated soft x-ray laser in collisionally pumped neon-like selenium, with emphasis on the ionization balance and excited state kinetics. The relative importance of various atomic processes, such as collisional excitation and dielectronic recombination, on the inversion kinetics will be demonstrated. We shall compare our models with experimental results and evaluate the success of this technique in predicting and analyzing the results of x-ray laser experiments. 22 refs., 5 figs., 3 tabs

Review of electron impact excitation cross sections for copper atom

Excitation of atomic copper by electron impact plays an important role in the copper vapor laser and accurate cross sections are needed for understanding and modeling laser performance. During the past seven years, there have been several attempts to normalize the relative elastic and inelastic cross sections measured by Trajmar and coworkers. However, each of these efforts have yielded different cross sections, and the uncertainty in the correct normalization of the data has been a source of confusion and concern for the kinetic modeling efforts. This difficulty has motivated us to review previous work on the electron impact excitation of copper atom and to perform new calculations of the inelastic cross sections using the impact parameter method. In this memorandum we review the previous attempts to normalize the experimental data and provide a critical assessment of the accuracy of the resulting cross sections. We also present new theoretical cross sections for the electron impact excitation of the /sup 2/S ..-->.. /sup 2/P/sup 0/ and /sup 2/S ..-->.. /sup 2/D transitions in copper. When the experimental cross sections are renormalized to the results of the impact parameter calculations, they are a factor of three smaller than those published in the latest paper of Trajmar et. al. At impact energies above 60 eV the excitation cross sections obtained with the impact parameter method agree well with the results of the very recent, unpublished, close-coupling calculations of Henry. This agreement suggests that the present normalization of the experimental cross sections is probably the most reliable one obtained to date

Pseudopotential theory of atomic and molecular rydberg states

In this paper we present a description of atomic and molecular Rydberg states using an effective Hamiltonian in the one-electron Hartree-Fock approximation. A pseudopotential is introduced to ensure the orthogonality of the Rydberg orbitals to the core. The core is represented by the ground-state wavefunction of the corresponding positive ion. In order to incorporate the pseudopotential formalism in a description of Rydberg states, the original pseudopotential theory is extended to the case where the core and valence orbitals are eigenfunctions of different one-electron operators. The formalism is applied to the triplet 5 states of helium and beryllium atoms and the results of numerical calculations are given. Good agreement with experiment is found. Possible extensions of the theory to more complex systems are discussed.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Dissociative recombination of interstellar ions: electronic structure calculations for HCO/sup +/

The present study of the interstellar formyl ion HCO/sup +/ is the first attempt to investigate dissociative recombination for a triatomic molecular ion using an entirely theoretical approach. We describe a number of fairly extensive electronic structure calculations that were performed to determine the reaction mechanism of the e-HCO/sup +/ process. Similar calculations for the isoelectronic ions HOC/sup +/ and HN/sub 2//sup +/ are in progress. 60 refs

XUV EMISSION FEATURES FROM THE LIVERMORE SOFT X-RAY LASER EXPERIMENTS

The measured wavelengths i n the soft x-ray region for 3p to 3s and 3d to 3p transitions in neon-, sodium-, and magnesium-like selenium are presented. The experimental results for the neon-like ions are compared to theoretical wavelength values and with values extrapolated along the isoelectronic sequence. The ions were contained in a plasma heated in a line-focus of a Nd-glass laser. The measurements were made with a time-gated microchannel-plate-intensified grazing incidence spectrograph