High-lying Resonance States Research Articles

Singlet fission in tetracene: an excited state analysis

Singlet fission is a potential mechanism to enhance the performance of current solar cells. However, the actual mechanism is still a matter of debate, with charge transfer states believed to play an essential role. The probability of the overall process can be related to the electronic coupling between the electronic states. Here, we explore the excited states of three pairs of tetracene with different relative orientation in the crystal structure showing different electronic couplings and identify the role of charge transfer states. First, a suitable theoretical method for the study of the tetracene pairs is determined by comparing time-dependent density functional theory with wave function-based methods in terms of excitation energies, so-called exciton descriptors, and graphical tools such as electron-hole correlation plots and natural transition orbitals. The results show the presence of low-lying charge transfer states in those tetracene pairs with non-zero electronic coupling, suggesting a superexchange-mediated mechanism, and high-lying charge resonance states for the pair with zero electronic coupling. Finally, the lower electron-hole correlation coefficients for pairs with non-zero coupling speak in favour of the superexchange-mediated mechanism, as a weaker Coulombic attraction due to the mixing with charge transfer states further facilitates the formation of the state from the photoexcited molecule.

High-lying doubly excited resonances in Ps− interacting with screened Coulomb potentials

The effect of screened Coulomb potentials on the high-lying doubly-excited resonance states of the positronium negative ion has been investigated using the method of complex-scaling together with employing highly correlated Hylleraas-type wave functions. Resonance parameters (resonance energy positions and widths) below the N = 4, 5, and 6 Ps thresholds for various screening parameters are determined.

Complex-rotation treatment on high-lying doubly-excited resonances in H − interacting with screened Coulomb potentials

In this work we present, for the first time, calculations of resonance energies and widths for some high-lying doubly-excited resonance states of H − embedded in plasmas using the complex-coordinate rotation method. Screened Coulomb potentials of Debye-type are used to simulate the plasma effects. Correlation effects between all the charged particles are taken into consideration by using Hylleraas-type wave functions. Our predicted results are converged with the basis lengths up to N = 715. For the lowest lying 2s 2 1S e state, good agreement has been found with an earlier calculation using the stabilization method. Results for the higher-lying 3s 2 1S e and 4s 2 1S e autoionization states of the plasma-embedded H − ion are the first calculations reported in the literature.

Contributions of high-n dielectronic satellites to krypton K-shell emission spectra

We report here on the calculation of dielectronic recombination resonance strengths for high-lying K-shell resonance states of He-, Li-, and Be-like krypton ions. For proper analysis of spectral data explicit calculations of satellite intensity factors are carried out for all possible intermediate resonance states with n = 2–10. Our calculations successfully predict the details of X-ray emission spectra of highly charged krypton ions interacting with electron beams.PACS Nos.: 32.30.Rj, 32.70.Cs, 32.80.Rm, 34.79.+e

High-lying resonance states of He and H

The diagonalization approximation is used to investigate the resonance states of He and H- respectively near the n = 4 and n = 5 hydrogen thresholds. Computations are carried out for states of 1,3 P0 symmetries; energies, total and partial widths of autoionization states of helium and autodetaching states of the negative hydrogen ion are calculated. Comparison is made with experiment and theory.

Dielectronic satellite spectra for high-lying resonance states of hydrogen-like iron and nickel

The wavelengths and satellite intensity factors of hydrogen-like iron and nickel are presented. The intermediate resonance states considered are |2lnl`LSJ> with n=5-8 and all possible values of l and l`. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock atomic model.

Dielectronic recombination from high-lying resonance states in H-like silicon, calcium, and iron.

We have calculated dielectronic recombination (DR) rate coefficients for H-like silicon, calcium, and iron at plasma temperatures 0.1--10 keV. The calculation involves all DR processes 1s+\ensuremath{\epsilon}${\mathit{l}}_{\mathit{c}}$\ensuremath{\rightarrow}(2lnl'${)}^{\mathrm{*}}$\ensuremath{\rightarrow}1sml''+\ensuremath{\gamma} with n=2-\ensuremath{\infty}. The effects of configuration interaction and spin-orbit coupling have been included for all states with n\ensuremath{\le}8; for higher-lying resonance states, the 1/${\mathit{n}}^{3}$ scaling was employed.

Laser-induced molecular stabilization and trapping and chemical bond hardening in intense laser fields

We study the intensity-dependent behavior of laser-induced vibrational quasi-energy (VQE) resonance structure and photodissociation rates of H 2 + molecular ions in intense laser fields at 775 nm and report a novel new high-intensity phenomenon. At strong fields, the vibrational levels are shifted and broadened substantially and break into several separate VQE resonance groups. distortion of the internuclear potential by the fields leads to the formation of various (field-dressed) adiabatic potential wells near multiphoton resonances which can support long-lived resonance states. The most striking finding is that high-lying VQE resonance states can in fact become more stabilized and longer lived at higher laser intensities, a phenomenon which may be termed as “bond hardening”. Time-dependent calculations confirm the laser-induced stabilization phenomenon and reveals that molecular population may be trapped simultaneously in different potential wells, at different internuclear separations (multiple well trapping).

Satellite spectra from high-lying resonance states for heliumlike Si, Ca, and Ti.

We report on the wavelengths and satellite intensity factors for selected heliumlike ions undergoing dielectronic recombination via several higher-lying resonance states, viz., the 1${\mathit{s}}^{2}$\ensuremath{\epsilon}${\mathit{l}}_{\mathit{c}}$\ensuremath{\rightarrow}1s2lnl'\ensuremath{\rightarrow}1${\mathit{s}}^{2}$ml'' with n=5, 6, 7, and 8. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock atomic model.

Satellite spectra for high-lying resonance states of heliumlike chromium and nickel.

We report on the wavelengths and satellite intensity factors of heliumlike nickel and chromium ions undergoing dielectronic recombinations via several high-lying resonance states. We have considered the process 1${\mathit{s}}^{2}$+\ensuremath{\epsilon}l\ensuremath{\rightarrow}(1s2lnl'${)}^{\mathrm{*}}$\ensuremath{\rightarrow}1${\mathit{s}}^{2}$ml''+\ensuremath{\gamma} for n=5, 6, 7, and 8 with all possible values of l and l', where n is the principal quantum number of the outermost electron of the doubly excited intermediate resonance state. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock model.

Resonance effects in elastic and first excited level inelastic neutron scattering on 12C from 15.0 to 18.25 MeV

In order to investigate the reaction mechanisms for elastic and first excited level ( I π = 2 +, E x = 4.44 MeV) inelastic n- 12C scattering, angular distributions of several observables have been measured: differential elastic cross sections at E n = 15.0, 15.85 and 18.25 MeV, elastic polarizations at E n = 15.85 MeV, differential inelastic cross sections and spin-flip probabilities at E n = 15.0, 15.85, 16.9 and 18.25 MeV, and inelastic analyzing powers and spin-flip analyzing powers at E n = 15.85 MeV. Neutron time-of-flight techniques with a scintillating scatterer have been used. Spin-flip data have been determined by means of the (n, n′ γ ⊥) correlation. Detailed comparisons of the experimental results were made with the predictions of collective-model CC calculations using the full Thomas form for the deformed spin-orbit potential. Large and energy-dependent spin-orbit deformations ( β 2 s. o. ≳ 3 β 2 c ) were needed indicating nuclear structure effects. The fit to the 15.85 MeV polarization data was considerably improved by adding d 3 2 and f 5 2 Breit-Wigner resonance amplitudes to the optical-model amplitudes. Inelastic scattering data were analyzed in terms of a microscopic antisymmetrized DWA in which high-lying resonance states are incorporated explicitly as doorway states. Higher-order processes are described by the addition of a phenomenological imaginary part to the transition potential. These analyses reveal the presence of a quadrupole resonance at about 21 MeV excitation in 12C. The results are also influenced to a lesser extent by the El giant dipole resonance and a dipole resonance at E x ≈ 19.5 MeV.