Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO

Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.     

Calculation of doubly excited even strontium states

The perturbation theory with zero order model potential has been successfully used for calculating the spectral characteristics (energies, radiative lifetimes, autoionization widths) of highly excited Rydberg and autoionization states of rare earths. Here, the same method is applied for investigating the 4dns, 4dnd and 4dng doubly excited Rydberg states of Sr. The obtained energies of the states are in good agreement with the experimental data of other authors. The calculation aims to give a more complete and reliable information about the experimentally observed spectra, as well as to predict the location of more highly excited states.     

Role of doubly excited states in calculations of optical activity

It is shown that doubly excited states play an important role in calculations of the optical activity of molecules with well-conjugated electron systems, such as the DNA bases. In some significant cases it is necessary to include a large number of excited states in the configuration interaction (CI ) to obtain a reliable, converging result. A new version of the CNDO/OPTIC method, which includes doubly excited states in the CI , is proposed. As an application, the electric transition moments in different pyrimidines are considered. The calculated results agree with experimental data and results obtained from ab initio calculations and INDO calculations using doubly excited states in the CI .     

Beam-foil study of doubly and singly excited states in BIII

Doubly excited⁴ L and² L systems of BIII have been studied by beam-foil spectroscopy. Spectra of boron (λ: 28.7–50.1 nm) have been recorded at Bochum with a resolution superior to that obtained previously. Eight new lines are classified in the⁴ L system and one in the² L system. The wavelength accuracy of most of the transitions already reported in the core-excited systems of BIII is greatly improved. On the basis of these results, six and two unidentified lines appearing in spectra recorded at Liège (λ: 50–200 nm) are classified in the⁴ L and² L core-excited systems, respectively. Where comparison with theoretical predictions by Chung et al. [1] is possible, excellent agreement is found for all the assigned lines. The first energy values are reported for seven terms in the doubly excited quartet system. Moreover, seven new lines are identified in the singly excited system of BIII.     

Metastable states in NO2+ probed with Auger spectroscopy

High-resolution N 1s and O 1s photoelectron spectra (PES) of NO are presented together with spectra of the subsequent Auger decay. The PES are analyzed by taking spin-orbit splitting of the (2)Π ground state into account providing detailed information on equilibrium distances, vibrational energies, and lifetime widths of the core-ionized states. In the Auger electron spectra (AES) transitions to five metastable dicationic final states are observed, with two of them previously unobserved. A Franck-Condon analysis of the vibrational progressions belonging to these transitions provides detailed information on the potential-energy curves of the dicationic final states as well as on the relative Auger rates. The present calculations of the potential-energy curves of NO(2+) agree well with the experimental results and allow an assignment of the two hitherto unresolved Auger transitions to excited states of NO(2+), C(2)Σ(+)and c(4)Π.     

One photon two electron excitations between doubly excited states of helium

Variational calculations using Hylleraas coordinates have been performed for the first time for estimating the energies of 3dnf((1,3)D(o)) state of helium for n=4,5,6. We predict absorption peaks at 12.219, 12.647, and 12.857 eV for the (3)D(o) series converging to N=3 ionization threshold of He(+) which can be expected to be observed in the experiment of single photon double excitation of lowest (3)P(e) state of helium placed in synchrotron radiation.     

Multiphonon decay of excited states of rare earth ions in crystals

Although the relaxation of excited electronic states through radiationless multiphonon processes has been well established by experiment, there are several serious problems concerning the current theoretical model in which the electron-phonon interaction is treated as a small perturbation, and the multiphonon transitions are attributed to high order expansion terms of perturbation theory. Here, we approach the problem in the framework of the adiabatic approximation. The rate of the multiphonon process is expressed in the form of the linear response time correlation function which is then evaluated by means of the saddle point approximation. The resulting expression predicts an approximately exponential dependence of the rate on the transition gap and a temperature dependence that agrees quantitatively with experiment.     

Calculation of highly excited autoionizing energy states of atomic sodium

Highly excited autoionizing levels of atomic sodium are calculated via an effective two electron-model. The results obtained are in good agreement with experimental data, proving the model to be valid.     

Effect of Debye plasma on the doubly excited states of highly stripped ions

Pilot calculations have been performed to study the effect of surrounding plasma on several doubly excited states for a few astrophysically important, highly stripped ions of helium isoelectronic sequence Al¹¹⁺, Si¹²⁺, P¹³⁺, S¹⁴⁺, and Cl¹⁵⁺. The transitions from 1s²:¹S^e → 2s²:¹S^e, 2p²:¹D^e, 2s2p:¹P^o, 2s3d:¹D^e and 2p3d:¹F^o are studied. The effect of the plasma background is taken care of using the Debye screening model which admits of a wide variety of plasma conditions. Transition energies as well as the analytical wave functions of the doubly excited states have been obtained from a study of the pole positions of the collective oscillation modes in the two‐electron charge cloud under a time‐dependent harmonic perturbation. The response properties of the system are analyzed from the linearized version of a suitably constructed variational functional. Most of the calculated data are new. Our results agree well with the relatively few existing experimental and theoretical data for the free ions. The general trend of the results show systematic behavior with respect to increased plasma strength, and the data may be useful from the astrophysical viewpoint. The doubly excited state wave functions have been used to calculate the Coulomb repulsion integrals to check their consistency and may be useful for evaluating other physical properties connected with transitions and also estimating the rate coefficients for dielectronic recombination processes, which play a major role in the diagnostic determination of high‐temperature plasmas. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Ab initio interatomic decay widths of excited states by applying Stieltjes imaging to Lanczos pseudospectra

Electronically excited states of atoms and molecules in an environment may decay in interatomic processes by transferring excess energy to neighboring species and ionizing them. The corresponding interatomic decay width is the most important characteristic of the decay allowing to calculate its efficiency and the final states' distribution. In this paper we present calculations of interatomic widths by the Fano-Stieltjes method applied to Lanczos pseudospectra, which has been previously shown to provide accurate autoionization widths in atoms and molecules. The use of Lanczos pseudospectra allows one to avoid the full diagonalization bottleneck and makes the method applicable to larger systems. We apply the present method to the calculation of interatomic decay widths in NeMg, NeAr and HCN[middle dot]Mg(n), n = 1, 2 clusters. The results are compared with widths obtained analytically and by other ab initio methods where available.     

Lyman-α excitation spectra in the photodissociation of the doubly excited states of H2

A Lyman-α excitation spectrum has been observed using synchrotron radiation in the energy region corresponding to the double electron excitation of H₂. There exist in the spectrum three thresholds at 26.6±0.5 eV, 29.2±0.7 eV and 30.9±0.6 eV, and a dip at 34.1±0.5 eV. A Lyman-α excitation spectrum in the energy region corresponding to the single electron excitation has been also observed using a detection system which works as a band pass filter for detecting of Lyman-α fluorescence. The cross section of Lyman-α fluorescence in the photodissociation of the doubly excited states is very small, e.g., in the order of 10^?20 cm² at 30 eV, in comparison with that from the single electron excitation.     

Photo-acoustic detection on electronic quenching rate constants of NO excited states

The electronic quenching rate constants of NO A(2)Σ (υ'=0, 1), E(2)Σ (υ'=2, 3, 4) and F(2)Δ (υ'=1, 2, 3) states by gas air are reported. The experiments were carried out by measuring the total fluorescence intensity of A(2)Σ (υ'=0, 1)→X(2)Π (υ″) transition at various air pressures. It gives the Stern-Volmer plots. The quenching rate constants of A(2)Σ (υ'=0, 1) states are obtained from the slope of Stern-Volmer plots and the known radiative lifetime. Based on the primary results of the work, we have measured the quenching rate constants of high excited E(2)Σ (υ'=2, 3, 4), F(2)Δ (υ'=1, 2, 3) states for the first time with the technique of photo-acoustic (PA) spectroscopy. It is shown that the electronic quenching rate constants of NO E (υ') and F (υ') states are in the order of 10(-10)cm(3)/molecules. They are much larger than those of A(2)Σ (υ') state, whose rate constants are in the order of 10(-13)cm(3)/molecules. For E (υ') and F (υ') states, it is also found that the quenching rate constants increase with the vibrational energy levels. Similar result has been reported also for A(2)Σ (υ'≥2) states in existing literatures. The agreement indicates the potential use of PA spectroscopy for measuring the electronic quenching rate.     

Unexpected properties of non‐autoionizing doubly excited states of the H2 molecule

We present accurate calculations of the non‐autoionizing and doubly excited states of the H₂ molecule using full configuration interaction with Hartree–Fock molecular orbitals and Heitler–London atomic orbitals. We consider the united atom configurations from He(2p2p) up to He(2p8g) and dissociation products from H₂(2p + 2p) up to H₂(2p + 6?). Born–Oppenheimer calculations are carried out with extended and optimized Slater‐type orbitals for a total of 40 states, 10 for each symmetry, covering the internuclear distances from the united atom to dissociation, which, for some states, is reached beyond 100 a₀. Occurrences of repulsive states cleanly interlaced between bound states with many vibrational levels are reported. Some of the potential minima are deep enough to accommodate many vibrational levels (up to 50). Noteworthy large equilibrium minima, like R_eq = 46.0 a₀ in the state dissociating as (2p + 6h) and with 18 vibrational levels. The occurrence of vertical excitations from the singly excited manifolds is analyzed. Several states present double minima generated by avoided crossings, some with a strong ionic character. © 2016 Wiley Periodicals, Inc.     

Highly excited states decay in p-terphenyl crystals. Magnetic field effect investigation

The magnetic field effect on the fluorescence of p-terphenyl crystals was investigated. It is shown that in aromatic crystals an important decay channel of highly excited states is autoionization followed by a triplet exciton creation by collision of the emitted electron.     

Very long-lived doubly vibrationally excited states above dissociation threshold: non-RRKM behavior in model triatomic systems

For couplings and mass ratios appropriate to molecules such as H₂O, D₂O, and CH₂ large volumes of the classical vibrational phase space are found to be non-dissociating even well above threshold. Fully quantum calculations yield families of exceptionally long-lived quantum states corresponding to these trapped volumes.     

Theoretical description of pressure shifts and quenching of excited atomic states in liquid helium

The pressure dependence of the linewidth and shift for the 2 ³S→2 ³P and 3 ³S→2 ³P transitions observed in electron-bombarded liquid helium is calculated by applying static line-broadening theory within the framework of a theoretical model. The calculated pressure shift, width and asymmetry are in good agreement with recent measurements over the pressure range of 1 to 25 atm. A new mechanism is proposed for the strong pressure quenching observed for several atomic and molecular emission lines.