Oscillator Strengths and Lifetimes for the P XIII Spectrum

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Received 3 May 2016; accepted 17 July 2016; published 20 July 2016

1. Introduction

2. Methodology

Computations of wavelengths made with the aid of a Hartree-Fock Relativistic (HFR) computer program package and a program of least-square procedure as given by Cowan [23] to adjust the values of the energetic parameters, comparing the data and calculating its consistency with the identification of known energy levels. The adjustable parameters are to be determined empirically to give the best possible fitting between the calculated eigenvalues and the observed energy levels. The fitting process is carried out by a self-consistent procedure until the parameter values no longer change from one iteration cycle to the next. The main purpose is to reach a fitting to the experimental energy levels, which minimizes the uncertainties as much as possible, using the least-squares method for each parity in which the standard deviation is less than one percent of the energy range covered by the energy levels. The optimized electrostatic parameters substitute their corresponding theoretical values and they are used again to calculate energy matrices, the determination of the oscillator strengths and lifetimes values. All strong configuration interactions are to be included and HFR method is used to given a better accuracy [24] . It should also be noticed, that at higher levels, the j-j notation is better and it should be used to estimate the percentages of compositions.

The oscillator strengths is a physical quantity related to line intensity I and transition probability, by:

, (1)

With, being m the electron mass, e their charge, γ the initial quantum state, , E(γ) the initial state energy and g = (2J + 1) is the number of degenerate quantum states with angular momentum J. Quantities with primes refer to the final state. In the equation above, the weighted oscillator strength, gf, is

, (2)

where, h is Planck’s constant; c is the light velocity; and a_{0} is the Bohr radius. The electric dipole line strength is defined by:

(3)

This quantity is a measure of the total strength of the spectral line, including all possible transitions between and J_{z} eigenstates. The tensor operator P^{1} (first order) in the reduced matrix element is the classical dipole moment for the atom in units of −ea_{0}. To obtain gf, we need to calculate S first, or its square root

. (4)

In a multiconfiguration calculation we have to expand the wavefunction in terms of single configuration wavefunction, , for both upper and lower levels:

(5)

Therefore, we can have the multiconfigurational expression for

(6)

The probability per unit time of an atom in a specific state γJ to make a spontaneous transition to any state with lower energy is

(7)

where is the Einstein spontaneous emission transition probability rate for a transition from the to the state. The sum is over all states with. The Einstein probability rate is related to gf through the following relation by:

(8)

Since the natural lifetime. The natural lifetime is applicable to an isolated atom.

The interaction with matter or radiation will reduce the lifetime of a state. The values for gf and lifetime given in Table 1 and Table 2, respectively, were calculated according to these equations. In order to obtain better values for oscillator strengths, we calculated the reduced matrix elements P^{1} by using optimized values of energy parameters which were adjusted from a least-squares calculation. In this adjustment, the code tries to fit experimental energy values by varying the electrostatic parameters. This procedure improves σ values used in Equation (2) and and values used in Equation (6).

Wavelength values in vacuum were converted to air by the relation [25] , , where the index of refraction of standard air (dry air containing 0.03CO_{2} by volume at normal pressure and) is

.

3. Results and Discussion

In our fitting process, the standard deviation reached for each parity as 12 cm^{−1} and 5 cm^{−1}, for even and odd configurations, respectively, is satisfactory for the aims of this work. Values for gf and lifetime given in Table 1 and Table 2, respectively, were calculated by the previously described method. Table 1 shows the results of the comparison between wavelength values as calculated by the method and the observed. In Table 2, we present lifetimes, energy levels and an estimation of their percentage composition. For the even-parity configurations we have the following picture: 1s^{2}5g, 1s^{2}6g, 1s^{2}6s, 1s^{2}7s, 1s^{2}8s, 1s^{2}7d, 1s^{2}8d, 1s2s^{2}, and the series 1s2pnp (3 ≤ n ≤ 4). For the odd-parity case we study the configuration 1s^{2}6h, and the series 1s^{2}nf (4 ≤ n ≤ 6), 1s^{2}np (5 ≤ n ≤ 8), 1s2snp (2 ≤ n ≤ 4). The interpretation of the configuration levels structure was made by least-squares fit of the observed levels and we propose the new values possible of the energy levels marked with asterisk (*) in the table. The oscillator strengths and lifetimes for the lithium-like ions are of astrophysical interest for photo-ionization modelling of elemental abundances in cosmic objects since an extensive data source is not currently available. Transitions in this ion have been of particular importance in extrapolation analysis especially for the dense spectra from N-like sequence in which the phosphorus is one element in isoelectronic sequence linking lighter elements where the analysis is more extensive. Is also an important testing ground for the development of theoretical methods which attempt to calculate atomic structure of many-electron systems.

4. Conclusion

We have presented oscillator strengths and lifetimes for all known transitions in P XIII. The gf-values are better agreement with line intensity observations and lifetime values that are closer to the experimental ones. We have been stimulated by the need to determine both important parameters in the study of plasma laboratory and solar

Table 1. Oscillator strengths and spectral lines for P XIII in the vacuum.

Table 2. (a) Even configurations. (b) Odd configurations.

(^{*}) Indicates an attempt to identify.

(^{*}) Indicates an attempt to identify.

spectra, as also phosphorus is an astrophysically important element. The present work is part of an ongoing program, whose goal is to obtain weighted oscillator strength, gf, and lifetimes for elements of astrophysical importance. Phosphorus occupies the fifteenth place with respect to cosmic distribution [26] .

References

[1] Moore, C.E. (1949) Atomic Energy Levels. Vol. 1, Circular of the National Bureau of Standards, Washington DC.

[2] Kelly, R.L. and Palumbo, L.J. (1973) Atomic and Ionic Emission Lines below 2000 Angstroms: Hydrogen through Krypton. NRL Report 7599, Tune.

[3] Fawcett, B.C. (1970) Classification of Highly Ionized Emission Lines due to Transitions from Singly and Doubly Excited Levels in Sodium, Magnesium, Alumninum, Silicon, Phosphorus, Sulphur, and Chlorine. Journal of Physics B, 3, 1152-1163. http://dx.doi.org/10.1088/0022-3700/3/8/017

[4] Fawcett, B.C., Hardcastle, R.A. and Tondello, G. (1970) New Classifications of Emission Lines of Highly Ionized Phosphorus and Sulphur. Journal of Physics B, 3, 564-571.

http://dx.doi.org/10.1088/0022-3700/3/4/011

[5] Goldsmith, S., Oren, L. and Cohen, L. (1973) Spectra of P XII and P XIII in the Extreme Vacuum Ultraviolet. Journal of the Optical Society of America, 63, 352-358.

http://dx.doi.org/10.1364/JOSA.63.000352

[6] Kasyanov, Y.S., Konomov, E.Y.A., Korobkin, V.V., Koshelev, K.N. and Serov, R.V. (1973) Intrashell Transitions in the Spectra Multicharged Phosphorus Ions. Optics and Spectroscopy (URSS), 35, 586-589.

[7] Dere, K.P. (1978) Spectral Lines Observed in Solar Flares between 171 and 630 Angstroms. Astrophysics, 221, 1062- 1067.

[8] Deschepper, P., Lebrunm, P., Palffy, L. and Pellegrin, P. (1982) Energy and Lifetime Measurements in Heliumlike and Lithiumlike Phosphorus. Physical Review A, 26, 1271-1277.

http://dx.doi.org/10.1103/PhysRevA.26.1271

[9] Edlen, B. (1983) Comparison of Theoretical and Experimental Level Values if the n = 2 Complex in Ions Isoelectronic with Li, Be, O and F. Physica Scripta, 28, 51-67.

http://dx.doi.org/10.1088/0031-8949/28/1/007

[10] Fawcett, B.C. and Ridgeley, A. (1981) Analysis of n = 3 to n = 4 Spectra for Ions from Mg X to Fe XXIV and P XI, XII. Journal of Physics B: Atomic and Molecular Physics, 14, 203-208.

http://dx.doi.org/10.1088/0022-3700/14/2/005

[11] Aglitskii, E.V., Boiko, V.A., Zakharov, S.M., Pikuz, S.A. and Faenov, A.Y.A. (1974) Observation in Laser Plasmas and Identification of Dielectron Satellites of Spectral Lines of Hydrogen- and Helium-Like Ions of Elements in the Na- V Range. Soviet Journal of Quantum Electronics, 4, 500-513.

http://dx.doi.org/10.1070/qe1974v004n04abeh006795

[12] Boiko, V.A., Faenov, A.Y. and Pikuz, S.A. (1978) X-Ray Spectroscopy of Multiply-Charged Ions from Laser Plasmas. Journal of Quantitative Spectroscopy & Radiative Transfer, 19, 11-50.

http://dx.doi.org/10.1016/0022-4073(78)90038-9

[13] Vainshtein, L.A. and Safronova, U. (1975) Wavelengths and Transition Probabilities for Ions. I ISAN Report, Troitsk, Russia, N6, 1-68.

[14] Vainshtein, L.A. and Safronova, U. (1978) Wavelengths and Transition Probabilities of Satellites to Resonance Lines of H- and He-Like Ions. Atomic Data and Nuclear Data Tables, 21, 49-68.

http://dx.doi.org/10.1016/0092-640X(78)90003-7

[15] (1980) Wavelengths and Transition Probabilities for Atoms and Atomic Ions—Part 1: Wavelengths; Part 2: Transition Probabilities. NSRDS-NBS, Washington DC, 68.

[16] Reader, J. and Corlis, C.H. (1982) Line Spectra of the Elements. In: Weast, R.C., Ed., CRC Handbook of Chemistry and Physics, 63rd Edition, CRC Press, Boca Raton.

[17] Martin, W.C., Zalubas, R. and Musgrove, A. (1985) Energy Levels of Phosphorus, P I through P XV. Journal of Physical and Chemical Reference Data, 14, 796-797. http://dx.doi.org/10.1063/1.555736

[18] Hayes, R.W. and Fawcett, B.C. (1986) The Spectrum of Phosphorus VI to XIII Between 22 and 92 Å. Physica Scripta, 34, 337-341. http://dx.doi.org/10.1088/0031-8949/34/4/009

[19] Kelly, R.L. (1987) Atomic and Ionic Spectrum Lines below 2000 Angstroms: Hydrogen through Krypton. Journal of Physical and Chemical Reference Data, 16, 1-1698.

[20] Hu, M.-H. and Wang, Z.-W. (2004) Oscillator Strengths for 22P - n2D Transitions of Lithium-Like Systems with Z = 11 to 20. Chinese Physics, 13, 1246-1250. http://dx.doi.org/10.1088/1009-1963/13/8/011

[21] Chen, C. and Wang, Z.-W. (2005) Oscillator Strengths for 2s2 - 2p2P Transitions of the Lithium Isoelectronic Sequence from NaIX to CaXVIII. Communications in Theoretical Physics, 43, 305-308.

http://dx.doi.org/10.1088/0253-6102/43/2/021

[22] Hu, M.-H. and Wang, Z.-W. (2009) Oscillator Strengths for 22S - n2P Transitions of the Lithium Isoelectronic Sequence from Z = 11 to 20. Chinese Physics B, 18, 2244-2249.

http://dx.doi.org/10.1088/1674-1056/18/6/023

[23] Cowan, R.D. (1981) The Theory of Atomic Structure and Spectra. University of California Press, Berkeley.

[24] Owens, J.C. (1967) Optical Refractive Index of Air: Dependence on Pressure, Temperature and Composition. Applied Optics, 6, 51-59. http://dx.doi.org/10.1364/AO.6.000051

[25] Fawcett, B.C. (1991) On the Accuracy of Oscillator Strengths. In: Wilson, S., Grant, I.P. and Gyorffy, B.L., Eds., The Effects of Relativity in Atoms, Molecules, and the Solid State, Springer, New York, 45-54.

[26] Aller, L.H. (1963) Distribution of the Chemical Elements. Foreign Literature Press, Moscow.