Bound excited states of atomic negative ions

Nicolaides, Cleanthes A.; Aspromallis, G.; Beck, Donald R.

doi:10.1016/0166-1280(89)80060-0

Cited by 25 publications

(20 citation statements)

References 82 publications

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“…From the accumulated knowledge in the field of computation of wave functions and properties of polyelectronic atoms, it can be deduced that solving the system of equations (5) reliably is a very demanding problem, even if supercomputers are available. It turns out that the use of state-specific wave functions for the discrete or the continuous spectrum [17,18] allows the incorporation of the important information while keeping the overall calculation manageable.…”

Section: A Choice Of the Interaction Operatormentioning

confidence: 99%

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Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

et al. 1994

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The problem of integrating the time-dependent Schrodinger equation (TDSE) describing the interaction of a polyelectronic atom with a laser pulse is treated by expanding the time-dependent wave function %(r, t) in terms of wave functions 4"E computed for discrete, autoionizing, and scattering states separately. The TDSE is transformed into a system of coupled first-order differential equations with time-dependent coeScients, whose number (in the thousands), necessary for convergence to be reliable, depends mainly on the degree of the contribution of the continuous spectrum, as a function of the frequency and strength of the field. This approach allows the systematic incorporation of the significant electronic structure, electron correlation, and spectral characteristics of each N-electron system under investigation. Furthermore, since the free-electron function is computed numerically in the polarized core potential of the remaining (N -1)-electron atom, properties such as the angular distribution and partial above-threshold ionization (ATI) of the photoelectron are directly computable. We present results from the application of our methods to H and Li . For the applications to H, which served as testing grounds for the method, the state-specific wave functions for discrete and continuum states were obtained numerically, for n and I up to 12 and 5, respectively, and for positive energies up to a= 34 eV with I up to 6. When comparisons with other time-independent and time-dependent results are possible, very good agreement is observed. On the other hand, our calculations do not confirm recent experimental results on absolute ionization rates for laser pulses of 248 nm. For Li, our results on ATI for photon energy tie=1.36 eV demonstrate the effects of initial-state electron correlation and of final-state fieldinduced coupling of open channels (the Li 1s 2s Sand 1s 2p P'), as a function of field intensity.

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Section: A Choice Of the Interaction Operatormentioning

confidence: 99%

“…These must contain the important effects of the self-consistent field and of interelectronic interactions. In this work, this is achieved by employing the electronic structure methods of the state-specific theory [17,18]. In which is revealed as a function of the field intensity.…”

Section: Introductionmentioning

confidence: 99%

Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

et al. 1994

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“…1 (12) satisfying Let +0 be a square-integrable configurationinteraction-type wave function representing an Xelectron resonance, and assume that it excludes the OCL correlating configuration, which we call g", . Let (25) i.e. , (cos5, ) Vo, -…”

Section: Localization Interpretation Of the Mchf Solutions And mentioning

confidence: 99%

Theory and computation of triply excited resonances: Application to states ofHe−

1993

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Autoionizing multiply excited states offer unusual challenges to the theory of electronic structure and spectra because of the presence of strong electron correlations, of their occasional weak binding, of their proximity to more than one threshold, and of their degeneracy with many continua. Here we discuss a theory that addresses these difFiculties in conjunction with the computation of their wave functions and intrinsic properties. Emphasis is given on the justification of the possible presence of self-consistently obtained open-channel-like (OCL) correlating configurations in the square-integrable representation of such states and on their effect on the energy E and the width I . Application of the theory has allowed the prediction of two hitherto unknown He triply excited resonances, the 2s2p P (E=59.71 eV, above the He ground state, I =79 meV) and the 2p D' (E=59.46 eV, I =282 meV) (1 a.u. =27.2116 eV).These resonances are above the singly excited states of He and are embedded in its doubly excited spectrum. The relatively broad 2p D' state interacts strongly with the He 2s2p P' ed continuum. The effect of this interaction has been studied in terms of the coupling with fixed core scattering states as well as with a self-consistently computed OCL bound configuration. The position of the He 2p' D' resonance is below that of the He 2p 'D autoionizing state at 59.91 eV and of the He 2p P bound state at 59.68 eV. The partial decay widths to the three important open channels are y(2s2p P')=252 meV, y(1s2p 'P')=21 meV, y(1s2p 'P')=9 meV. The final core states are also represented by correlated (multiconfigurational Hartree-Fock) functions. The 2s2p P state couples to four neighboring He thresholds, the 2s2p P', 2p P, 'D, and 2s2p 'P'. It is above the He 2s2p P' threshold at 58.31 eV, with respect to which it is a valence shape resonance, and below the He 2p 'D and 2s2p 'P' autoionizing states. In the limit of an exact energy calculation, we suggest that its position would also come below that of the 2p P state, which it overlaps. Its partial widths are y(2s2p P') =60 meV, y(1s2p P') =9 meV, y(1s2p 'P') =10 meV. The present results, considered together with published ones on other n=2 intrashell states, show that the recently measured [R. N. Gosselin and P. Marmet, Phys. Rev. A 41, 1335] closely lying structures at 58.415 and 58.48 eV cannot correspond to the He 2p S' and D' states, as these authors proposed.PACS number(s): 31.50.+w, 31.20.Tz, 32.80.Dz, 34.80.Dp

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“…The observed discrepancy between the two measurements and the lack of any theoretical predictions on the cross section and angular distribution of process (1) [4]. ) As with many other such states, in the Hartree-Fock (HF) approximation this state is unbound.…”

mentioning

confidence: 99%

“…(1) I'+ Is. (1) I' (4) (1) =~( ls"(1) I'+ Is,(1)I'), (5) while for j, =2, the parity-unfavored case, P(2) = -1,…”

mentioning

confidence: 99%

Asymmetry parameter and total cross section for the photodetachment of the metastableBe−1s2
Sinanis
¹
,
Komninos
²
,
Nicolaides
³

1995
Phys. Rev. A
18
0
0
0
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We report the results of calculations of the asymmetry parameter and of the cross section for the photodetachment of the metastable state Be 1s 2s2p P, for photoelectron energies above the Be 1s 2s2p P' threshold of 0.74 -2.74 eV. The calculations were based on configuration-interaction-type wave functions, where the final scattering state is obtained via the solution to all orders of multichannel reaction (K) matrices. Very good agreement is observed with the recent measurement of Pegg et al. [Phys. Rev. A 50, 3861 (1994)]. PACS number(s): 32.80.Fb In a recent publication, Pegg et al. [1]reported the results of measurements of the single-photon detachment cross section o. and of the asymmetry parameter P at photon energy A, cu=2.076 eV for the process Be 1s 2s2p P+Acu+Be 1s 2s2p Po+ configuration-interaction (CI) methods with appropriate boundary conditions. The two quantities tr(s) and P(c) were computed from the definitions of Dill and Fano [10] (for reviews on the definition and calculation of photoionization observables see Refs. [11] -[13]): (ss and sd), (1)~( e) = 2~(it), (2) where a = 1.815 eV, according to the experimental value for the detachment threshold [2]. The o was measured to be 31 3 Mb, in serious disagreement with the only previously reported measurement, by Bae and Peterson [3], who found o.=9~5 Mb. The P was measured to be 0.49~0.02. No other measurements or theoretical results exist for these properties. The observed discrepancy between the two measurements and the lack of any theoretical predictions on the cross section and angular distribution of process (1) have led us to undertaking the calculation of o. (s) and P(s) in the photon energy range 1.0 -3.0 eV. This range includes the one previously examined [3] (1.65 -2.34), and corresponds to photoelectron energies above the Be 1s 2s2p P' threshold of 0.74 -2.74 eV. The Be ls 2s 2p P state belongs tp the class of excited states of atomic negative ions, which are bound. (For a recent review see Ref. [4]. ) As with many other such states,in the Hartree-Fock (HF) approximation this state is unbound. However, the fact that symmetry does not allow any hole-filling pair correlations (which would cause decay), and that the correlation energy of the three Be L-shell electrons (2s2p P) is larger than that of the Be (2s2p P') pair, turns the Be 1s 2s2p P state into a discrete one [5,6]. Its first observation and identification were reported in [3,7]. Its existence was also verified from the observation [8] of the Be 1s 2p 5 -1s 2s2p P transition, whpse, possibility, wavelength, and probability had been predicted theoreticallyThe present calculations were carried out in the framework of the state-specific theory of photoionization processes [9], which uses separately optimized wave functions that are expansions over symmetry-adapted bound and scattering configurations, whose coefficients are obtained by 1 P(s)=, 2~(it)P(i ),

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Bound excited states of atomic negative ions

Cited by 25 publications

References 82 publications

Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

Theory and computation of triply excited resonances: Application to states ofHe−

Asymmetry parameter and total cross section for the photodetachment of the metastableBe−1s2
Sinanis
¹
,
Komninos
²
,
Nicolaides
³

1995
Phys. Rev. A
18
0
0
0
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Bound excited states of atomic negative ions

Cited by 25 publications

References 82 publications

Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

Computation of strong-field multiphoton processes in polyelectronic atoms: State-specific method and applications to H andLi−

Theory and computation of triply excited resonances: Application to states ofHe−

Asymmetry parameter and total cross section for the photodetachment of the metastableBe−1s2Sinanis1, Komninos2, Nicolaides3 1995Phys. Rev. A18000View full textAdd to dashboardCite

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About

Asymmetry parameter and total cross section for the photodetachment of the metastableBe−1s2
Sinanis
¹
,
Komninos
²
,
Nicolaides
³

1995
Phys. Rev. A
18
0
0
0
View full text Add to dashboard Cite