Measurement Of Oscillator Strengths Research Articles

Electron impact measurement of oscillator strengths for dipole‐allowed transitions of atomic oxygen

Optical oscillator strengths for the seven most intense dipole‐allowed transitions in the 100‐eV incident energy electron scattering spectrum of atomic oxygen have been measured from forward scattering spectra. An apparatus was used in which a microwave discharge source, producing atomic oxygen seeded in a helium beam, was coupled to an electron spectrometer. The O ¹D population in the target beam was less than 1.5% of O ³P, and transitions from the O ³P ground electronic state only were observed. The performance of the apparatus was checked by measurement of optical oscillator strengths for helium and atomic hydrogen. Agreement with the National Bureau of Standards (NBS) values for a single spectrum of better than 10% was obtained for three He transitions and 13% for the atomic hydrogen n = 3 transitions when the He 1¹S ‐ 2¹P and H n = 1 ‐ n = 2 Lyman series transitions were normalized to the NBS values. The atomic oxygen 2p4 ³P ‐ 2p³3s ³S° (1304 Å) transition was normalized to an average experimental value of f = 0.048. Optical oscillator strengths obtained for the other transitions were 2p4 ³P ‐ 2p³4s ³S° (1040 Å), 0.010±0.002; 2p4 ³P ‐ 2p³3d ³D° (1026 Å), 0.019±0.001; 2p4 ³P ‐ 2p³3s′ ³D° (989 Å), 0.061±0.006; 2p4 ³P ‐ 2p³4d ³D° (972 Å), 0.016±0.006; 2p4 ³P ‐ 2p³3s″ ³P° (878 Å), 0.086±0.006; 2p4 ³P ‐; 2s2p5 ³P° (792 Å), 0.070±0.004. (All values have ±5% uncertainty in addition to the experimental scatter as indicated.) The electric dipole‐forbidden transition 2p4 ³P ‐ 2p³3p ³P was also observed as a weak process.

Ba oscillator strengths from a laser-excited vapor.

We describe a method for evaluating the consistency of oscillator strengths in the neutral and ionized species of an atom. The method is based on the constant number density of a dense vapor. In our procedure the vapor is excited and then ionized within less than 1 \ensuremath{\mu}s by resonant laser irradiation. The column densities ${N}_{i}$${l}_{i}$ of the levels that are appreciably occupied during the excitation and ionization are sampled by absorption, emission, and/or anomalous-dispersion measurements in a set of suitable spectral lines. Given correct oscillator strengths ${f}_{i}$ for these lines, the column density ${\mathcal{J}}_{i}$ ${N}_{i}$${l}_{i}$ (which is actually determined from the measured quantities ${N}_{i}$${f}_{i}$${l}_{i}$) will remain constant while excitation and ionization take place. In barium---with diagnostics based on accepted f values in the literature---the column density appeared reduced by a factor of 2 during the initial portion of the excitation, i.e., while only the low-lying levels of neutral barium were predominantly excited. Upon complete ionization, the column density took again the value derived before the laser irradiation, when all atoms had been in the ground state. From this behavior we concluded that the literature oscillator strengths for absorption lines involving the neutral ground state and the ground state and low-lying levels of ${\mathrm{Ba}}^{+}$ were consistent on a relative scale, but that the f values for absorption transitions from the low-lying metastable levels and from the resonance level of neutral barium were too large by a factor of 2. We recommend a set of correction factors to be applied to the existing data in the literature. Our conclusions are supported by the results of a critical analysis of recent oscillator strength and lifetime measurements for neutral barium.

Comments on the Measurement of Transition Probabilities

Developments in the measurements of oscillator strengths, that are of current and future interest to astrophysics, have taken place in the past few years:– there is increased emphasis on methods which are independent of level populations (i.e., of number densities and thus equilibrium in the vapour or plasma under investigation),–clear progress has been made towards higher precision (and accuracy) and–the dynamic range of astrophysically relevant oscillator strengths was further extended towards weaker lines.

Geometry-independent, phase-matched measurement of a vacuum-ultraviolet oscillator strength in xenon

A new method for accurately measuring the oscillator strengths of gases is presented. The technique is based on determining the phase-matching conditions for four-wave mixing in a gas mixture. When high gas pressures are used, the measurement is independent of the detailed spatial-mode properties of the laser. By using the known refractive index of argon as a reference, the oscillator strength of the xenon ground-state-to-7s [3/2](1) transition at 117.04 nm was found to be 0.098 +/- 0.012.

Measurement of relative oscillator strengths for Mn I. Transitions from levels in the range 0 eV < < 3 eV

We present relative oscillator strengths for 58 lines of Mn I for a range of + 0.19 > log(gf) > −3.795 in the excitation interval 0eV < χ < ∼ 3 eV. The measurements have been made to a relative accuracy of better than 2 per cent using the Oxford furnace tehnique, with full allowance for hyperfine structure using the data of Booth et al. The relative values have been placed on an absolute scale using published lifetime data, to an accuracy of about 7 per cent for the ground state lines and 3 per cent for the excited state lines.

Measurement of relative oscillator strengths for Cr I lines – I. Measures for transitions from levels a7S3 (0.00 eV), a5S2 (0.94 eV) and a5D0−4 (0.96−1.03 eV)

Mesures des forces d'oscillateur relatives de 49 raies de Cr I avec des energies d'excitation jusqu'a 1,03 volts

Interstellar O2. II - VUV oscillator strengths of Schumann-Runge lines and prospects for Space Telescope observations

Interstellar molecular oxygen should be detectable in interstellar clouds through observation of its absorption lines in the spectra of background stars. This paper describes and presents the results of measurements of oscillator strengths for some lines in the vacuum ultraviolet (VUV) spectrum of O2. Lines of the (13, 0) through (16, 0) bands of the B 3Sigma(-)u - X 3Sigma(-)g, Schumann-Runge system between 1760 A and 1790 A will be the most suitable for searches for absorption by interstellar O2 with the High Resolution Spectrograph on Space Telescope. The strongest lines in these bands have oscillator strengths of about 3 x 10 to the -5th.

Measurements of Lifetimes and Oscillator Strengths of Neutral and Singly Ionized Atoms. Experimental Results of the Last Five Years

After a short description of the standard methods to determine f-values and atomic lifetimes, the most important development of the last years - the application of pulsed dye lasers - is discussed and some results are compared. The further development in the field of f-value measurement is described by some typical activities: emission and absorption measurements with thermal light sources and the application of emission and absorption branching ratio measurements. The general accuracy which can be obtained with the different measuring methods is discussed.The article does not comprehend the whole work which has been done in this field since 1977. There appeared a large number of articles which are not mentioned because of the necessarily limited volume of such a survey. Especially, the treatment of the beam foil technique which yields a lot of lifetimes for singly ionized atoms is omitted completely.

Calibration of oscillator-strength measurements for the principal-series transitions of potassium

Oscillator-strength measurements have been calibrated against the radiative lifetime for the 4s-4p transition of potassium. This yields a value of (8.1 + or - 0.5) times 10 to the -21 sq cm for the photoionization cross section at the series limit, and implies a value for the cross-section minimum in good quantitative agreement with that calculated by Seaton (1951).

Measurements of Oscillator Strengths for the Transitions from the Metastable 3P Levels of Alkaline-Earth Atoms. IV. Calcium–High-n Members

Oscillator strengths ( f values) for the transitions 4 s 4 p 3 P –4 s n d 3 D with n =6 to 12 and -3 d 5 s 3 D of Ca have been determined relative to those of the multiplet 4 s 4 p 3 P –4 p 2 3 P by means of the hook method. The resulting f values are 12–35% smaller for n =6, 7 and 8 than the data of NBS compilation by Wiese et al. Those for other members are first reported in this paper. The spectral density of the f values is found to have a minimum value around 3 d 5 s 3 D and 4 s 9 d 3 D . This behavior is quantitatively explained by means of a multichannel quantum defect theory.

Measurement of oscillator strengths in the ultraviolet by magneto-optical rotation

By combination of plane-polarised synchrotron light and a close-ruled holographic 3 m concave grating, of high resolution, the authors have observed-in addition to the first resolved Zeeman structures to be reported below 2000 AA-magnetic rotation patterns of lines of Rydberg series. They have used these patterns as a basis of a flexible and accurate method for measurement of relative f values, usable in the Schumann region. Some results, at somewhat longer wavelengths, for Sr I are compared with earlier results obtained by the 'Hook method'.

Precision measurement of relative oscillator strengths for Ti II - I. Transitions from levels Formula (0.12-0.15 eV)

Precision measurement of relative oscillator strengths for Ti II - I. Transitions from levels Formula (0.12-0.15 eV)

Measurement of relative oscillator strengths for Fe I: transitions from levels Formula (2.61 eV - 2.56 eV). Use of a multipass optical system

Measurement of relative oscillator strengths for Fe I: transitions from levels Formula (2.61 eV - 2.56 eV). Use of a multipass optical system

Precision measurement of relative oscillator strengths for Ti I - II. Transitions from levels Formula(1.5-1.07 eV)

Precision measurement of relative oscillator strengths for Ti I - II. Transitions from levels Formula(1.5-1.07 eV)

The solar abundance of tungsten

Recent measurements of Wi oscillator strengths (Obbarius and Kock, 1982) lead to a solar photospheric abundance of tungsten, log ɛW = 1.06 ± 0.15 on the scale log ɛH = 12. The solar W/Si abundance ratio, 0.32 W atoms/106 Si, coincides with that found in carbonaceous chrondrites. Implications for solar-system r-processes abundances are pointed out.

Solvent effect on intensities of hypersensitive bands of lanthanide perchlorates

The measurements of oscillator strengths of hypersensitive bands for Ln(ClO 4) 3 (Ln  Nd, Ho, Er) in different solvents are reported. The sesults are discussed within the framework of the polarizability mechanism.

Measurements of Oscillator Strengths for the Transitions from the Metastable 3P Levels of Alkaline-Earth Atoms. III. Calcium–Low-n Members

Oscillator strengths ( f values) for the transitions 4 s 4 p 3 P –4 s n d 3 D with n =6 to 12 and -3 d 5 s 3 D of Ca have been determined relative to those of the multiplet 4 s 4 p 3 P –4 p 2 3 P by means of the hook method. The resulting f values are 12–35% smaller for n =6, 7 and 8 than the data of NBS compilation by Wiese et al. Those for other members are first reported in this paper. The spectral density of the f values is found to have a minimum value around 3 d 5 s 3 D and 4 s 9 d 3 D . This behavior is quantitatively explained by means of a multichannel quantum defect theory.

Measurements of Oscillator Strengths for the Transitions from the Metastable 3P Levels of Alkaline-Earth Atoms. II. Magnesium

Oscillator strengths ( f values) for the transitions 3 s 3 p 3 P –3 s n s 3 S ( n =4 and 5), -3 s n d 3 D ( n =4 and 6 to 9) and -3 p 2 3 P in Mg I have been determined by using the hook method. The metastable 3 s 3 p 3 P levels have been populated by a DC discharge of the Mg–He mixture. The absolute scale is based on the absolute f values for 3 s 3 p 3 P –3 s 3 d 3 D (∼0.62). The determined f values are in good agreement with recent theoretical predictions. An estimate of the photoionization cross section from the 3 P levels by extrapolating the f values results in 20.2 Mb at the threshold.

Measurements of Oscillator Strengths for the Transitions from the Metastable 3P Levels of Alkaline-Earth Atoms. I. Strontium

Measurements of Oscillator Strengths for the Transitions from the Metastable ³<i>P</i> Levels of Alkaline-Earth Atoms. I. Strontium

Precision measurement of relative oscillator strengths - IX. Measures of Fe I transitions from levels Formula

Measurements are presented of the relative oscillator strengths of 52 lines of Fe I, with excitation energies of between 2.18 and 2.49 eV, and with |$\text{log}\,{gf}\,\gt\,-3.23$|⁠, made using the Oxford furnace technique. These measures have a relative accuracy of 0.004 dex (1 per cent). Absolute values are also given with an accuracy of 2.5 per cent, assuming |$\text{log}\,{gf}\,(371.99)\,=\,-0.43\,\pm \,0.01$| (2.3 per cent). Comparisons are made with other experimental data and with the results of theoretical calculations. An expression is proposed for correcting the measured oscillator strengths of Corliss & Warner to give data having an rms deviation from the Oxford values of 0.14 dex, compared with an rms deviation of 0.55 dex for uncorrected data. Measures previously published for six lines are regarded as unsafe, chiefly because of uncertain blending, and these are withdrawn. The previous measurement for λ 381.453 is corrected.