Differential oscillator strengths and dipole polarizabilities for transitions of the helium sequence

Khan, F.; Khandelwal, G. S.; Wilson, J. Warren

doi:10.1103/physreva.38.6159

Cited by 5 publications

(3 citation statements)

References 30 publications

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“…In summary, the continuum moments S,(p) and L J p ) are determined in this paper using the Zf values chosen in order to satisfy the known sum rules for S(l) exactly and S(-2) approximately in the hope that both the high as well as low and intermediate excitation energy regions of dflde would essentially be reproduced. Previously, in Khan et al (1988b) only S ( -2 ) was fitted exactly with S(0) fitted approximately. The high excitation energy part of df / d e has thus improved significantly as is evident from the close agreement of S(2) with those determined from sum rule (Drake 1982(Drake , 1988 displayed in table 3.…”

Section: Results Of Calculationsmentioning

confidence: 99%

“…The moments S ( p ) and L ( p ) of equations ( 1) and ( 2) can thus be calculated by knowing the discrete and continuum oscillator strength values of the screened hydrogenic model. The method of determining the parameters 2, and 2, for knowing the discrete and the continuum oscillator strength values is already described (Khan et al 1988a, b, Khandelwal et a1 1989a. The evaluation of the moments S ( p ) for p = 1 and 2, however, deserves special attention.…”

Section: Introductionmentioning

confidence: 99%

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Moments of dipole oscillator-strength distribution for the helium sequence

Khan

Khandelwal

Wilson

1990

J. Phys. B: At. Mol. Opt. Phys.

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The moments S(mu) for -6 < or = mu < or = 2 and L(mu) for mu = 0, 1 and 2 are calculated for the helium sequence for atomic numbers Z up to 30 under a screened hydrogenic model. In this model, one describes the atom by single-particle hydrogenic wavefunctions and treats the initial and the final state as characterised by two different effective charge parameters Zi and Zf, respectively. An asymptotic expansion is made of the differential oscillator strength of the screened hydrogenic model. Assuming the value 287.6 for the coefficient of the term epsilon -7/2 for helium atom as given by Salpeter and Zaidi, the parameter Zf is determined for the helium sequence. This approach has resulted in values which are in reasonable agreement with the various moment values of other authors.

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Section: Results Of Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Moments of dipole oscillator-strength distribution for the helium sequence

Khan

Khandelwal

Wilson

1990

J. Phys. B: At. Mol. Opt. Phys.

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“…There is no essential reason for preferring this method to another except the desire to restrict the size of the pseudostate basis. Looking at the behaviour of the oscillator strength for transitions from the ground state to the 'P continuum (Khan et al 1988), it may be seen that three-point Gauss-Laguerre integration permits evaluation of the contributions to the polarizability and to the oscillator strength sum to accuracies of 4% and 6% respectively. ,…”

Section: Introductionmentioning

confidence: 99%

Pseudostate bases including an L²description of the continuum for use in e^--He collision calculations

Tweed¹,

Langlois²

1991

J. Phys. B: At. Mol. Opt. Phys.

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The possibility of constructing a distorted-wave second Born approximation model for electron-helium collisions at energies above 30 eV is examined. It is proposed to calculate the second Born term by analytic integration over the intermediate momentum of the colliding electron and by replacing the infinite sum over intermediate target states by a finite sum over a pseudostate expansion. A method is proposed for obtaining pseudostate bases which approximately reproduce known bound-state contributions to the oscillator strength sum rules for n3,1 S to n3,1 P transitions and polarizabilities of the 11 S, 21 S and 23 S states. These bases are composed of 'exact' n3,1 S, n3,1 P and n3,1 D states up to n=3 and of a restricted number of 3,1 S, 3,1 P and 3,1 D L2 -type pseudostates. Certain of the latter lie in the continuum and their energies are adjusted to correspond to quadrature points for Gauss-Laguerre integration, this in order to easily evaluate the continuum contributions to oscillator strength sums, polarizabilities and second Born terms.

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