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Results for “transition probability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Relative transition probabilities of cobalt

Results of determinations of neutral-cobalt transition probabilities measured relative to Co I 4150.43 A and Co II 4145.15 A, using a gas-driven shock tube as the spectroscopic light source. Results are presented for 139 Co I lines in the range from 3940 to 6640 A and 11 Co II lines in the range from 3840 to 4730 A, which are estimated to have reliabilities ranging from 8 to 50%.

Roig, R. A.↗
NASA NTRS1984

Measurements of transition probabilities for spin-changing lines of atomic ions used in diagnostics of astrophysical plasmas

The intensities of ultraviolet, spin-changing, 'intersystem' lines of low-Z atomic ions are frequently used in determinations of electron densities and temperatures in astrophysical plasmas as well as in measurements of element abundances in the interstellar gas. The transition probabilities (A-values) of these lines, which are about five orders of magnitude weaker than allowed lines, have not been measured heretofore and various calculations produce A-values for these lines that differ by as much as 50 percent A radio-frequency ion trap has been used for the first measurements of transition probabilities for intersystem lines seen in astronomical spectra. The measurement procedure is discussed and results for Si III, O III, N II, and C III are reviewed and compared to calculated values. Discrepancies exist; these indicate that some of the calculated A-values may be less reliable than has been beleived and that revisions to the electron densities determined for some astrophysical plasmas may be required.

Smith, P. L.↗
DOE OSTI2020

Accurate CI-MBPT calculation of radiative lifetimes and transition probabilities of neutral lanthanum (La I) odd states with J = 3/2

In this work, an accurate calculation of radiative lifetimes and transition probabilities of the first 21 odd states with a total angular momentum J = 3/2 was performed for La I using configuration-interaction many-body perturbation theory (CI-MBPT). A technique to obtain correct transition amplitudes was devised for pairs of states with substantial mixing that improved the theoretical accuracy. The results were compared to known experimental and theoretical data for the considered transitions. It has been shown that the transition data calculated with CI-MBPT and with corrections for pairs of mixed states are in good agreement with the latest experimental data of Den Hartog et al, 2015 J. Phys. B: At. Mol. Phys. 48, 155 001, better than other theoretical results. The transition data can find many applications in astrophysics, and the CI-MBPT formalism with mixing correction is applicable to other atoms similar to or more complex than La I.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Theoretical electric quadrupole transition probabilities for Ca, Sr and Ba

The 1D-1S quadrupole transition probabilities for Ca, Sr and Ba have been computed using extended GTO and STO valence basis sets and configuration-interaction wavefunctions that include the important core-valence correlation effects. For Ba and Sr, the relativistic contraction of the core orbitals was accounted for in the GTO calculations by a relativistic effective-core potential. The computed Einstein coefficient for Ca of 39.6/s is in excellent agreement with the recent experimental value of 40 + or - 8/s. The best Einstein coefficients for Sr (44.7/s) and Ba (2.98/s) imply increasing quadrupole line strengths down the column. Relativistic effects substantially increase the quadrupole Einstein coefficient for Ba.

Bauschlicher, C. W., Jr.↗
NASA NTRS1990

Transition probabilities and Franck-Condon factors for the second negative band system of O2(+)

Transition probabilities for the second negative band system of O2(+) are computed using the dipole transition moment presented by Wetmore et al. (1984). Vibrational levels v double prime = 0 - 54 of the X2Pi(g) ground state and v prime = - 33 of the excited A2Pi(u) state are included. Franck-Condon factors for ionization-excitation of O2 to O2(+) are also presented.

Fox, J. L.↗
NASA NTRS1982

Calculation of radiative transition probabilities and lifetimes

Procedures for calculating bound-bound and bound-continuum (free) radiative transition probabilities and radiative lifetimes are summarized. Calculations include rotational dependence and R-dependent electronic transition moments (no Franck-Condon or R-centroid approximation). Detailed comparisons of theoretical results with experimental measurements are made for bound-bound transitions in the A-X systems of LiH and Na2. New bound-free results are presented for LiH. New bound-free results and comparisons with very recent fluorescence experiments are presented for Na2.

Zemke, W. T.↗
NASA NTRS1973

K-LL Auger transition probabilities for elements with low and intermediate atomic numbers

Radiationless K-LL transition probabilities have been calculated nonrelativistically in j-j coupling and in intermediate coupling, without and with configuration interaction, for elements with atomic numbers from 13 to 47. The system is treated as a coupled two-hole configuration. The single-particle radial wave functions required in the calculation of radial matrix elements, and in the calculation of mixing coefficients in the intermediate-coupling scheme, were obtained from Green's atomic independent-particle model. Comparison with previous theoretical work and with experimental data is made. The effects of intermediate coupling, configuration interaction, and relativity are noted.

Chen, M. H.↗
NASA NTRS1982

Laser-excitation technique for the measurement of absolute transition probabilities of weak atomic lines

A new technique is presented for the measurement of transition probabilities for weak allowed, intersystem, and forbidden lines. The method exploits the fact that oscillator strength is proportional to the number of stimulated absorptions and emissions produced by a narrow-band laser pulse of known energy which is in resonance with an atomic transition. The method is tested for a particular transition of Mg I with a known oscillator strength value and of appropriate magnitude. The number densities are measured using a Mach-Zehnder interferometer and the hook method for the lower level population and by measuring an absorption-equivalent width for the other. The apparatus consisted of a high-power tunable laser and a magnesium oven to produce excited Mg vapor, and a laser-plasma background continuum. The results are in good agreement with theoretical and other experimental data.

Kwong, H. S.↗
NASA NTRS1985

Theoretical transition probabilities between the lowest 2S, 2P and 2D states of Na, K, Rb and Cs

Theoretical transition probabilities between the lowest 2S, 2P and 2D states of the alkali atoms Na through Cs have been computed using near Hartree-Fock quality Slater basis sets. The important core-valence correlation effects are incorporated explicitly by a configuration-interaction procedure. For Cs, the calculations were repeated using a Gaussian basis set so that relativistic effects could be incorporated through an effective core potential procedure. The best calculated electric quadrupole Einstein coefficients are Na(196.3/s), K(103.6/s), Rb(72.4/s) and Cs(19.7/s). Core-valence effects become increasingly important down the column, and reduce the quadrupole transition strengths to about the same degree as for the 2P-2S and 2D-2P dipole-allowed transitions. Relativistic effects increase the quadrupole moment of Cs, but less so than in Ba, presumably because the alkali 2D states are more diffuse.

Langhoff, S. R.↗