Measurement Of Oscillator Strengths Research Articles

Oscillator strength measurements in Pr II with the fast-ion-beam laser-induced-fluorescence technique

The spontaneous-emission branching fractions of 32 levels of Pr II were measured by the fast-ion-beam laser-induced-fluorescence technique. The levels studied had energies from ∼21 500 to ∼29 000 cm−1, and the decay branches detected were in the range from 250 to 850 nm. The experimental uncertainties are within 10%. Using our previously measured radiative lifetimes, we determined the Einstein A coefficients and oscillator strengths for 260 transitions. The results are important for stellar elemental abundance determinations.

The need for branching fraction measurements in multiply-charged ions

Much progress has been made in the measurement of oscillator strengths in neutral and singly-ionized atoms, providing a database for use in important applications. However, for multiply-charged ions, measured data for oscillator strengths are almost exclusively limited to low-lying unbranched transitions. Although extensive measurements of ionic lifetimes exist, the lack of branching fraction measurements in multiply-charged ions prevents these data from being converted to oscillator strengths. A significant factor leading to this deficiency involves the lack of adequate line intensity calibration standards in the vacuum ultraviolet spectral region 2000–400 Å. Here we review the interrelationships connecting these rate parameters, indicate some of the important applications for which they are needed, describe the experimental limitations that currently exist, and suggest possible methods for extending these measurements below 1000 Å.

Oscillator strength measurements of the 3p ↦ nd Rydberg transitions of sodium

We report new measurements of the oscillator strengths of the 3p 2P3/2 ↦nd 2D5/2, 3/2 and 3p 2P1/2 ↦ nd 2D3/2 Rydberg transitions of sodium using a thermionic diode ion detector in conjunction with the Nd:YAG pumped dye lasers. The ns 2S1/2 and nd 2D5/2,3/2 Rydberg series have been recorded via two-step excitation, from the 3p 2P3/2 and 3p 2P1/2 intermediate states. Employing the saturation technique, the photoionization cross sections from the 3p 2P3/2 and 3p 2P1/2 intermediate states at the first ionization threshold are determined as 7.9(1.3) Mb and 6.7(1.1) Mb respectively. The f-values of the Rydberg transitions are calibrated with the photoionization cross section measured at the first ionization threshold and compared with the earlier data.

Atomic oscillator strengths in the spectral domain ofGaia

This paper presents the results of a detailed investigation of the validity of oscillator strengths in the spectral domain of the Gaia spectrometer 848-875 nm. This analysis is performed by fitting the most significant Fe I and Si I solar lines in this spectral range with synthetic profiles calculated by 3D radiative hydrodynamical (RHD) simulations. Our main conclusion is that the laboratory oscillator strengths agree well (< 0.1 dex) with values derived from 3D simulations, whereas the semi-empirical values found in data bases like the Vienna Atomic Line Database are imprecise, with a disagreement that can be as large as 1 dex. We address this conclusion to laboratories to encourage new oscillator strength measurements in the infrared, especially in the Gaia region.

Fast-ion-beam laser-induced-fluorescence measurements of spontaneous-emission branching ratios and oscillator strengths in Sm II

We measured the spontaneous-emission branching ratios of 69 levels in Sm II selectively populated via single-frequency laser excitation of a 10 keV ion beam. The levels studied had term energies up to 29 600 cm–1, and decay branches with spontaneous emission in the range 250–850 nm were detected. The experimental accuracy was in the range of 10%. We used these branching ratios along with our previously determined radiative lifetimes to infer transition probabilities and oscillator strengths for 608 transitions in the wavelength range 363–771 nm, which are useful for stellar abundance determinations.PACS Nos.: 32.70.Cs, 95.30.Ky

Measurements of rovibronic line oscillator strengths of N2 in the 83.4 nm region: A high‐resolution high‐temperature study

We report the rovibronic line oscillator strengths of N2 in the 83.4 nm region at high temperatures measured by using ultrahigh‐resolution photoabsorption spectroscopy. The measurements have been carried out using a resolution of 6.5 × 10−4 nm and at temperatures of 600, 535, and 295 K. The N2 absorption features in the 83.4 nm region mainly involve the (0,0) band of the c′6‐X transition and the weaker (2,0) band of the c4‐X and the (25,0) band of the b′–X transitions. Spectral perturbation effects in the c′6‐X transition have been observed at J (rotational quantum number) &gt;14. The presence of weak transitions and hot band transitions further contribute to the spectral complexity, especially in the long wavelength side. By integrating over each individual absorption profile for each rotational line up to J = 16, the rovibronic line oscillator strengths of the (0,0) c′6‐X transition of N2 are measured. For the spectral regions with strong perturbations and overlapping by the weak (2,0) c4‐X and the (25,0) b′–X transitions, we have measured the effective oscillator strength values with a roughly equal spectral step covering the perturbed features in the 83.422–83.477 nm region. The present results will contribute to a correct interpretation of the OII 83.4 nm EUV airglow emission of the Earth by elucidating the effect of temperature on the atmospheric extinction due to absorption by N2 and O2.

Measurements of oscillator strengths of the 2p5(2P1/2)nd J = 2, 3 autoionizing resonances in neon

Oscillator strengths of the 2p5(2P1/2)nd J = 2, 3 autoionizing resonances in neon have been determined using a dc discharge plasma in conjunction with an Nd:YAG pumped dye laser system. The excited states are approached using two-step laser excitation via 2p53p′[1/2]1, 2p53p′[3/2]1 and 2p53p′[3/2]2 intermediate states which are accessed from the 2p53s [1/2]2 metastable state, populated by the discharge in the hollow cathode lamp. The f-values have been determined for the nd′[3/2]2, nd′[5/2]2 and nd′[5/2]3 series following the ΔK = ΔJ = +Δℓ selection rule. Employing the saturation technique the photoionization cross section at the 2p5 2P1/2 ionization threshold is determined as 5.5(6) Mb and consequently the f-values of the nd′ J = 2, 3 autoionizing resonances have been extracted.

Oscillator strength and linewidth measurements of dipole-allowed transitions in N214 between 93.5 and 99.5nm

Line oscillator strengths in 16 electric dipole-allowed bands of 14N2 in the 93.5-99.5 nm (106,950-100,500 cm(-1)) region have been measured at an instrumental resolution of 6.5 x 10(-4) nm (0.7 cm(-1)). The transitions terminate on vibrational levels of the 3psigma 1Sigma u (+), 3ppi 1Pi u, and 3ssigma 1Pi u Rydberg states and of the b' 1Sigma u (+) and b 1Pi u valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J'(J'+1) and are extrapolated to J'=0 in order to facilitate comparisons with results of coupled-Schrodinger-equation calculations that do not take into account rotational interactions. Most bands in this study reveal a marked J dependence of the f values and/or display anomalous P-, Q- and R-branch intensity patterns. These patterns should help inform future spectroscopic models that incorporate rotational effects, and these are critical for the construction of realistic atmospheric radiative transfer models. Linewidth measurements are reported for four bands. Information provided by the J dependences of the experimental linewidths should be of use in the development of a more complete understanding of the predissociation mechanisms in N2.

Experimental oscillator strengths for the spectrum of neutral manganese

We report laboratory measurements of oscillator strengths for 44 transitions in the Mn T spectrum covering the wavelength range 209-2780 nm. Nine energy level lifetimes have been measured using time resolved laser-induced fluorescence (LIF). The lifetimes have been combined with branching fractions measured by Fourier transform spectroscopy to obtain absolute oscillator strengths. In total, 24 of these oscillator strengths are measured for the first time, including transitions in the previously unobserved infrared region above 2.0 mu m.

The influence of hyperfine structure on some manganese line profiles in the solar spectrum

Taking into account effects of hyperfine structure, we calculated the synthetic solar spectrum for wavelength intervals around nine neutral manganese lines. To estimate values of hyperfine components we used the Oxford total absorption oscillator strength measurements (Booth et al. 1983). We compared observed profiles (Photometric Atlas of the Solar Spectrum from 3000 to 10000 ?(Delbouille et al. 1973)) of selected manganese lines with synthesized profiles in two cases: when hyperfine structure is not and when it is taken into account. By comparing the calculated with observed spectrum, we corrected the total oscillator strengths of all nine selected manganese lines.

CF A 2Σ+–X 2Π and B 2Δ–X 2Π study by broadband absorption spectroscopy in a plasma etch reactor: Determination of transition probabilities, CF X 2Π concentrations, and gas temperatures

Broadband absorption spectroscopy was applied to study the CF A 2Σ+–X 2Π and B 2Δ–X 2Π transitions in a plasma etch reactor. We report a previously unobserved band, which is assigned as CF A 2Σ+–X 2Π (3,0). This band is significantly broadened by predissociation, and we estimate the average collision-free lifetime of the CF A 2Σ+ v′=3 level to be 0.30±0.08 ps. Experimental relative oscillator strength measurements, together with ab initio calculations, Rydberg–Klein–Rees-based wave functions and experimental lifetimes were used to calculate a full set of transition probabilities for the CF A 2Σ+–X 2Π and B 2Δ–X 2Π bands. The maximum observed number densities of CF X 2Π were ∼2×1013 cm−3 with sensitivity to measure to 1010 cm−3. The excited state and ground state temperatures were determined by comparing the spectra to simulations. The ground state rotational temperature was 450±30 K and the vibrational temperature was 850±80 K near the substrate surface. The CF B 2Δ excited state rotational temperatures are higher than those of the ground state. We show that this absorption technique is practical for determining gas temperatures and absolute concentrations in plasma etch reactors.

ZnO as a Material Mostly Adapted for Realisation of Room-Temperature Polariton Lasers

Wannier-Mott excitons in the wurzite-type semiconductor material ZnO are stable at room temperature, have an extremely large oscillator strength and emit purple light. This makes ZnO an excellent potential candidate for the fabrication of room-temperature lasers where the coherent light amplification is ruled by the fascinating mechanism of the Bose-condensation of the exciton-polaritons. We first report on the direct optical measurement of the exciton oscillator strength f in ZnO. The longitudinal transverse splitting of the exciton resonances Γ 5 (B) and Γ 1 (C) are found to achieve record values of 5 and 7 meV, respectively, that is two orders of magnitude larger than that in GaAs. Secondly, we propose a model ZnO-based microcavity structure that is found to be the most adapted structure for the observation of the polariton laser effect. We thus can compute the phase diagram of the lasing regimes. A record value of the threshold power of 2 mW per device (at power density of 3000 W/cm 2 ) at room temperature is found for the model laser structure.

ZnO as a material mostly adapted for the realization of room-temperature polariton lasers

Wannier-Mott excitons in the wurzite-type semiconductor material ZnO are stable at room temperature, have an extremely large oscillator strength, and emit blue light. This makes ZnO an excellent potential candidate for the fabrication of room-temperature lasers where the coherent light amplification is ruled by the fascinating mechanism of the Bose condensation of the exciton polaritons. We report the direct optical measurement of the exciton oscillator strength f in ZnO. The longitudinal transverse splitting of the exciton resonances Γ 5 (B) and Γ 1 (C) are found to achieve record values of 5 and 7 meV, respectively, that, is two orders of magnitude larger than in GaAs. Second, we propose a model ZnO-based microcavity structure that is found to be the most adapted structure for the observation of the polariton laser effect. We thus can compute the phase diagram of the lasing regimes. A record value of the threshold power of 2 mW per device (at power density of 3000 W/cm 2 ) at room temperature is found for the model laser structure.

Measurement of absolute dipole oscillator strengths for pyridine: photoabsorption and the molecular and dissociative photoionization in the valence shell (4–200 eV)

Absolute photoabsorption oscillator strengths for the valence shell of pyridine have been measured using dipole (e,e) spectroscopy at high resolution (∼0.05 eV FWHM) and low resolution (∼1 eV FWHM) from 4 to 30 eV and from 5 to 200 eV, respectively. The absolute photoabsorption oscillator strength scale (±5%) has been determined using valence shell TRK (i.e. S(0)) sum-rule normalization. The accuracy of the absolute scale has been verified using the S(−2) sum rule and literature values of the dipole polarizability. The low resolution photoabsorption results have been combined with time of flight mass spectral data measured using dipole (e,e+ion) coincidence spectroscopy (∼1 eV FWHM), to determine the absolute oscillator strengths for the molecular and dissociative photoionization of pyridine at equivalent photon energies from the first ionization threshold up to 60 eV.

Precision measurements of the total photoionization cross-sections of He, Ne, Ar, Kr, and Xe

Absolute photoionization cross-sections for the rare gases have been measured from threshold to 125 eV with an accuracy of ±1 to 3% and are presented in both tabular and graphical form. These data are compared with the optical oscillator strength measurements of Brion and co-workers, who used the Dipole (e, e) collision technique.

Line Oscillator Strength Measurements in the d (7)– X (0) and e (4)– X (0) bands of CO

Laboratory measurements of line oscillator strengths in the bands of carbon monoxide currently provide an incomplete data set for the interpretation of astronomical observations in the vacuum ultraviolet region. We report line f-values in two intersystem bands, d3Δ(v = 7)-X 1Σ+(v = 0) at 146.4 nm and e3Σ-(4)-X(0) at 147.1 nm, from photoabsorption spectra recorded with an instrumental resolution of 7.6 × 10-4 nm (resolving power ~190,000). The high-resolution measurements (1) minimize line saturation effects in the determination of f-values and (2) allow for the direct experimental determination of the f-values of low-J lines that contribute to interstellar absorption features. We compare our measured line f-values with those generated from the intersystem band model of Rostas and coworkers. We find the predictions of relative line f-values within each band to be in agreement with the measurements, but there are discrepancies in the absolute scale. Based on this comparison, we present recommended f-values for low-J rotational lines within each band.

Measurement of Oscillator Strengths in Uranium Using Laser Techniques

Laser Isotope Separation of Uranium (Atomic Vapor Laser Isotope Separation, «AVLIS») has stimulated, these last 20 past years, a number of studies on oscillator strength measurements. This interest for oscillator strength measurements is related to the importance of this parameter for scaling a future plant, since this parameter determines the laser fluences needed for effective atomic photoionization. This presentation will review several techniques (saturation, branching ratio + lifetime, Rabi oscillations, Autler-Townes) which have been used by CEA at Saclay. Examples of results for atomic uranium are given, advantages and disadvantages, accuracy and limitations of each method are discussed.

A Search for Interstellar CH2toward HD 154368 and ζ Ophiuchi

We have searched for molecular CH2 in the interstellar gas in the line of sight to HD 154368 and ζ Oph to constrain further the gas-phase chemistry of carbon-bearing molecules in the cool, translucent clouds toward these stars. We report tentative detection of CH2 in the interstellar spectra of both stars. In ζ Oph, slight depressions in the stellar continuum are seen near 1410.1 and 1415.8 A corresponding to band structure in CH2, while in HD 154368 a single, narrow feature is found at 1410 A that may be due to CH2. Assuming that these features are produced by CH2, the column densities of CH2 toward HD 154368 and ζ Oph are (5.9 ± 3.1) × 1013 cm-2 (Wλ1410.1 = 5.2 mA) and (3.3 ± 1.9) × 1013 cm-2 (Wλ1415.8 = 29 mA), respectively. Although the oscillator strengths for the relevant electronic transitions are somewhat problematic, our deduced column densities are within a factor of 2-5 of those predicted by the model chemistry. These observations may represent the first detection of CH2 interstellar absorption in any astronomical object. Additional theoretical estimates and laboratory measurements of relevant oscillator strengths are needed to provide more accurate estimates of CH2 column densities and stronger constraints on the carbon chemistry in these interstellar molecular clouds.

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Large discrepancies in the published photoabsorption oscillator strengths of the vacuum-ultraviolet (VUV) bands of CO hamper the interpretation of VUV astronomical observations. We report new oscillator strength measurements of the (0, 0) and (1, 0) bands of the CO B1Σ+-X1Σ+ electronic system determined from high-resolution (resolving power ≈ 750,000) absorption spectra recorded with a tunable VUV laser system. The instrumental bandwidth (~ 0.14 cm-1 FWHM) was significantly less than the widths of the Doppler-broadened CO lines (~ 0.20 cm-1 FWHM). The B(0)-X(0) and B(1)-X(0) band oscillator strengths, derived from measurements of the photoabsorption cross sections of 36 individual rotational lines, are (6.5 ± 0.6) × 10-3 and (1.1 ± 0.1) × 10-3, respectively. Our results are compared with other recent laboratory measurements and with ab initio calculations.

Selected Lifetime and Oscillator Strength Measurements in Siii

We have remeasured the lifetimes of the 3s24s and 3s25s2S1/2 levels in Si II using beam foil spectroscopic techniques. Measured values for the lifetimes and oscillator strengths derived from them are presented and compared with previous measurements and theoretical calculations. Agreement with recent theoretical calculations is now quite good: for 3s24s it is excellent and for 3s25s it is satisfactory, although the theoretical uncertainties in that calculation are still somewhat larger than desired.