High-lying doubly excited states of He and H<Superscript>−</Superscript>: electron correlations and classification schemes

High-lying doubly excited states of He and H⁻ are studied and energies and intrinsic characteristics of their wave-functions are reported. Results for energies of ³P ^o and ¹D doubly excited states associated with the hydrogenic thresholds up to N = 20 are presented and compared to available data from the literature. The classification of these doubly excited states by approximate quantum numbers is reexamined.     

Energy Levels of Doubly Excited States in Argon

Term energies of doubly excited states in argon and argon ions have been determined using single-configuration Hartree-Fock calculation. The energies calculated for KL3s3p⁶nl and KL3s⁶3p⁴nln1 states of Ar show a fairly good agreement with the experimental results obtained by various techniques. However, for Ar+, Ar²+, Ar²+ and Ar³+ states there are no experimental data available in the literature for comparison.     

Doubly excited 2s2p 1,3P1 resonances in photoionization of helium

The multi-configuration Dirac-Fock（MCDF） method is implemented to study doubly excited 2s2p ^1,3P₁ resonances of the helium atom and the interference between photoionization and photoexcitation autoionization processes.In order to reproduce the total photoionization sprectra,the excited energies from the ground 1s^{2 1}S₀ state to the doubly excited 2s2p ^1,3P₁ states and the relevant Auger decay rates and widths are calculated in detail.Furthermore,the interference profile determined by the so-called Fano parameters q and ρ² is also reproduced.Good agreement is found between the present results and other available theoretical and experimental results.This indeed shows a promising way to investigate the Fano resonances in photoionization of atoms within the MCDF scheme,although there are some discrepancies in the present calculations of the 2s2p ³P₁ state.     

Two-phonon states in doubly even nuclei with 30 ≦ Z ≦ 52

Results of a survey of energies of two-phonon states are presented. Systematic trends are extracted and parametrized with the anharmonic vibrator model. The doubly even nuclei with anomalous 0⁺ first excited states are fitted into a general pattern indicating profound influence of both proton and neutron shell closure on the lowering of the 0^+' state energies. A sharp transition from anharmonic vibrational to almost pure rotational motion in this nuclear region is suggested for nuclei with first excited 2⁺ state energy ≈ 130 keV. Such a possible transition and similar ones already well known in the rare earth and heavy element regions are well described by the model.     

Doubly-Excited 1,3 P o States of H− Interacting with Screened Coulomb (Yukawa) Potentials

We have investigated the doubly excited 2s2p ³ P ^o and 2s3p ¹ P ^o resonance states of H⁻ embedded in a model plasma environment. Plasma effects are taken care of by using a screened Coulomb (Yukawa-type) potential. Correlated wave functions are used to represent the correlation effect between the charged particles. The density of resonance states has been calculated using the stabilization method. The calculated resonance energies and widths for various screening parameters are reported.     

<Emphasis Type="Italic">D</Emphasis>-Wave Resonances in Three-Body System Ps<Superscript>−</Superscript> with Pure Coulomb and Screened Coulomb (Yukawa) Potentials

We have investigated the doubly excited ¹ D ^e resonance states of Ps⁻ interacting with pure Coulomb and screened Coulomb (Yukawa) potentials employing highly correlated wavefunctions. For pure Coulomb interaction, in the framework of stabilization method and complex coordinate rotation method we have obtained two resonances below the n = 2 threshold of the Ps atom. For screened Coulomb interaction, we employ the stabilization method to extract resonance parameters. Resonance energies and widths for the ¹ D ^e resonance states of Ps⁻ for different screening parameter ranging from infinity (pure Coulomb case) to a small value are also reported.     

类钠Ni~(17+)离子双电子复合过程理论研究

使用基于相对论多组态方法的FAC程序,研究了类钠Ni17+(3s)离子通过双激发态Ni16+(3pnl,3dnl)(Δn=0激发)的双电子复合过程,得到了态选择的双电子复合截面和速率系数,并与文献中的实验和理论数据进行了对比.结果发现,计算通过3p3/210l和3p1/211l共振态的双电子复合积分截面在实验误差范围内与实验测量很好地符合,并好于全相对论的多体微扰理论计算结果.结合量子亏损理论,发现包含高里德伯态的共振双激发态的辐射跃迁和自电离速率具有较好的标度关系,利用该关系给出了近激发阈值的所有共振态的双电子复合积分截面和速率系数.比较3pnl和3dnl两个系列,发现在低温(大约小于100eV)等离子体情况下前者速率系数比后者大,更高的温度后者大.     

Observation of intense low energy autoionization lines in the wings of the forward peak from fast ion-atom collisions

In the ejected electron spectra from collisions of C²⁺, O⁴⁺ and Si^10,11,12+ with argon toms at energies of 2–4 MeV/amu, a series of intense lines has been observed, which originates from doubly excited autoionizing states of Belike projectiles. These lines correspond to electron energies between 2 and 20 eV in the projectile frame. For kinematic reasons these lines can only be detected near the forward direction.     

Screening constant by unit nuclear charge calculations for (n s2)1Se, (np2)1De and (N s n p)1P○ excited states of He-like systems

Screening Constant by Unit Nuclear Charge (SCUNC) is a new analytical method suitable for the treatment of the properties of He-like systems. In this paper, the possibilities of the method are demonstrated for calculating in the framework of semi-empirical procedure, total energies, total electron-electron interaction energies and excitation energies for (ns²)¹S^e, (np²)¹D^e and (Nsnp)¹P° doubly excited states of He-like ions. The proposed semi-empirical scheme, leads to accurate results in good agreement as well as with available other theoretical results than experimental data.     

CASPT2 and CCSD(T) calculations of dipole moments and polarizabilities of acetone in excited states

The acetone molecule is investigated in its ground state and valence ^1,3n-π*, ^1,3π-π*, and ^1,3σ-π* excited states and Rydberg ^1,3n-3s, ^1,3π-3?, ^1,3n-3p_y and ^1,3π-3p_y states using the CASSCF, CASPT2, and CCSD(T) methods. Equilibrium geometries of excited states are obtained and their changes with respect to the ground state are discussed. For most excited states the C_2v symmetry of the ground state is lowered to the C_s symmetry. A series of valence vertical and adiabatic excitation energies is presented along with excitation energies for Rydberg states. The main body of the paper contains Finite-Field Perturbation Theory (FFPT) calculations of electric properties of the vertically as well as geometry relaxed excited states. Dipole moments of valence excited states decrease significantly upon excitation, being about one half of the ground state dipole moment. Polarizabilities usually change upon excitation much less (increase by about 30%) but hyperpolarizabilities are enhanced up to one or two orders of magnitude. The orientation of the dipole moment is reversed in some vertically excited Rydberg states. Properties of the ground and excited states are discussed considering alterations of the electronic structure and shifts in the geometry.     

Doubly Excited <Superscript>1,3</Superscript><Emphasis Type="Italic">P</Emphasis><Superscript>e</Superscript> Resonance States of the Positronium Negative Ion with Coulomb and Screened Coulomb Potentials

We have investigated the doubly excited ^1,3 P ^e resonance states of positronium negative ion with Coulomb and screened Coulomb potentials using highly accurate correlated exponential wavefunctions. For Coulomb interaction, the stabilization and the complex-rotation methods are employed to extract resonance parameters (resonance positions and widths). We have obtained two ¹ P ^e resonances and three ³ P ^e resonances below the n = 3 Ps threshold. In addition to Feshbach resonances lying below n = 3 Ps threshold, we have calculated one ³ P ^e shape resonances lying above the Ps (n = 2) threshold. For screened Coulomb (Yukawa) interaction, we employ the stabilization method to extract resonance parameters as functions screening parameter. The resonance energies and widths for ^1,3 P ^e resonance states of Ps⁻ below the n = 3 Ps threshold for different screening parameters ranging from infinity (Coulomb case) to small values are reported, along with the Ps(3S) and Ps(3P) threshold energies. The screened Coulomb results for the ^1,3 P ^e resonance states are reported for the first time in the literature.     

Energies and electron correlation effects in two-electron doubly excited (nl)2 states

Energies of singlet doubly excited states 2p^{2 1}D, 3d^{2 1}G, 4f^{2 1}I of He isoelectronic series are calculated in the framework of the variational method by using Hylleraas-type wave functions and a real Hamiltonian. The results obtained show quantitatively the importance of electron correlation effects in the doubly excited states and they are in good agreement with some experimental data and other theoretical results. Received 30 March 2000 and Received in final form 4 July 2000     

Theoretical study of molecular properties of low-lying electronic excited states of H2O and H2S

Geometries, excitation energies, dipole moments and dipole polarisability tensor components of the ground and four lowest excited states ³ B ₁, ¹ B ₁, ³ A ₂, ¹ A ₂ of the H₂O and H₂S molecules were calculated at the CASSCF, CASPT2, CCSD and CCSD(T) level of approximation. Vertical excitation and equilibrium transition energies of these states, having the Rydberg character, are reported too. Properties of both molecules in the ground and in low lying excited states are compared and discussed from the point of view of their molecular electronic structure. Upon excitation we observe dramatic changes of dipole moments and polarisabilities with respect to the ground state. We stress the change of the polarity of H₂O in all excited states accompanied by the enhancement of the dipole polarisability by an order of magnitude. Large, even if less pronounced, are changes of electric properties of H₂S in its excited states. Dipole moments and dipole polarisabilities of ³ B ₁, ¹ B ₁ states of H₂S and H₂O behave quite analogously in comparison to their respective ground state. The general pattern of properties for both molecules in their ³ A ₂ and ¹ A ₂ excited states is more different due to a pronounced participation of the sulphur d-orbitals in these states of the H₂S molecule.     

Doubly excited triplet states of highly stripped ions

Transition energies, Coulomb repulsions and effective quantum numbers have been calculated for the doubly excited Nsnp: ³P⁰ (for N = 2, n = N,?, 5n = N,\ldots, 5); Nsnd: ³D^e (for N = 2, n=N+1, ?, 5n=N+1, \ldots, 5) and Npnd: ³F⁰ (for N = 2, n=N+1, ?, 5n=N+1, \ldots, 5) states for the highly stripped ions Na⁹⁺{\rm Na^{9+}}, Mg¹⁰⁺\rm Mg^{10+}, Al¹¹⁺\rm Al^{11+}, Si¹²⁺\rm Si^{12+}, P¹³⁺\rm P^{13+} and S¹⁴⁺\rm S^{14+}. Time-dependent perturbation theory has been applied to calculate such transitions properties. A time-dependent harmonic perturbation causes simultaneous excitation of both the electrons with a change of spin state. The doubly excited energy levels and the analytic representation of their wave functions are obtained by identifying the poles of an appropriately constructed linearized variational functional with respect to driving frequency. Most of the results are new. The transition energies and effective quantum numbers of 2s2p: ³P⁰ states of all the ions agree well with the only available experimental data.     

甲基乙烯基硅酮在外场作用下的光激发特性研究

采用密度泛函B3P86和组态相互作用方法在6-311++G^**基组水平上计算了甲基乙烯基硅酮分子从基态到前10个激发态的跃迁波长，振子强度，自发辐射系数A_n0和吸收系数B_0n(n＝1—10).同时研究了外电场对甲基乙烯基硅酮分子激发态的影响规律.结果表明，随外电场强度增大，最高占据轨道与最低空轨道能隙变小，激发能随电场增加而急剧减小.因而表明在外电场作用下，分子易于激发和 关键词： 甲基乙烯基硅酮 激发态 外电场     

Anomalies in Elastic Scattering at Isobaric Analogue States

Excitation functions for proton elastic scattering on Mn⁵⁵ at proton energies from 1320 KeV to 1480 KeV have been measured at the angles 135° and 150°. Anomalies in the differential elastic scattering were observed at E_p = 1350 ± 4 KeV, 1385 ± 4 KeV and 1445 ± 4 KeV respectively. These resonance states are the isobaric analogues of the ground, first excited and second excited states in Mn⁵⁶ respectively. Analysis of the results showed that these resonance states are best fitted to a J^π = 3⁺, 2⁺ and 1⁺ which is in excellent agreement with the J^π values of the corresponding states in Mn⁵⁶. The total widths and proton widths of these states were determined.     

Alpha-induced fragmentation of 28Si in a statistical model

Within the context of a statistical model, that incorporates final-state interaction between a pair of fragments, we have calculated the energy spectra associated with the production of different isobaric pairs as a function of their lab kinetic energy and isobaric and elemental distributions of nuclei produced in the ⁴He$ + $²⁸Si reaction at cm incident energies of 102.7, 173.7, 300, 500, and 1000MeV. Double differential cross-section of isobars 16, 20, and 24 as a function of their lab kinetic energies at 30^° and the same for isobar 24 at 10^°, 30^°, 60^°, and 90^° have been calculated at cm incident energies of 102.7 and 173.7MeV and compared with the data of Woo et al. Calculated yields follow the trend of the data at each angle, and calculated angular distributions also reproduce the general trend of the observed ones. A key feature of the model is that it allows for fragments to be emitted in ground states as well as in excited states that are allowed by the conservation of energy. The analysis establishes that the fragments are emitted in excited state. The excitation energies for A = 24 and 16 are deduced from the data. The observed angular distributions for A = 7, 12, 16, 20, 24, and 28 are well accounted for assuming them to be emitted in excited states. The relative production probabilities for different elements and isobars are energy dependent. The yields for unstable elements, ⁵Li, ⁸Be, and ²⁶Al, are found to be significant. The relative fragmentation probabilities of all allowed isotopic pairs have been presented.     

Structure and bonding of the (C6H6)+ 2 radical

To elucidate the relative stability of various structures of the benzene dimer cation radical, (C₆H₆)⁺ ₂ in its ground and low-lying excited states, ab initio complete active space self-consistent field (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations were performed. Full optimization was performed at the CASSCF level for various structures of the dimer cation, followed by MRSDCI and MRCPA calculations. It was found that the global minimum of the cation is at a slipped C_2h sandwich structure but there are some other sandwich structures with almost the same stability, being within about kcal mol^?1. T-shape structures are less stable than the sandwich structures, by more than 5 kcal mol^?1 by MRCPA calculations. Low lying electronic excited states in various structures are also discussed.     

Doubly excited states of positronium negative ions

A physical interpretation of the recently calculated doubly excited states of Ps^– is given. The available resonance parameters obtained by using the method of complex-coordinate rotation indicate that the doubly excited (e^–e⁺e^–) system would behave very much like an XYX triatomic molecule.     

Evidence for quartet structures in the nickel region

It has been found that, in several nickel and zinc doubly even isotopes, a small number of levels are strongly and selectively excited at low energies by the (¹⁶O, ¹²C) α-transfer direct reaction, performed on iron and nickel targets near the Coulomb barrier. The behaviour of these states, together with calculations performed in the stretch scheme, strongly suggest that they involve a quartet structure, namely two protons and two neutrons in a highly symmetric configuration. The α-cluster model, which was successful in light nuclei, has now found a general and natural extension in medium-weight nuclei, in terms of quartet states which expresses the importance of four-nucleon correlations in nuclear structure.