Absolute Optical Oscillator Strengths Research Articles

Erratum: Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution. III. The photoabsorption of argon, krypton, and xenon

Erratum: Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution. III. The photoabsorption of argon, krypton, and xenon

Absolute optical oscillator strengths for discrete and continuum photoabsorption of molecular nitrogen (11–200 eV)

Absolute optical oscillator strengths for the photoabsorption of molecular nitrogen in the energy region 11–200 eV have been determined using low resolution (1 eV fwhm) dipole (e, e) spectroscopy. The absolute scale was obtained by TRK sum-rule normalization. High resolution (0.048 eV fwhm) dipole (e, e) spectroscopy has been used to measure the absolute optical oscillator strengths for the excitation of molecular nitrogen in the valence shell discrete region. The measurements are free of the “line saturation” (bandwidth) effects which complicate direct photoabsorption studies using the Beer-Lambert law. Absolute optical oscillator strengths for excitation to individual vibronic bands of the b 1Π u and b′ 1Σ + u valence excited states, the c 1Π u, c′ 1Σ + u and o 1Π u Rydberg states and also the e 1Π u and e′ 1Σ + u states have been obtained. The present results are compared with previously published experimental data and theoretical calculations.

Absolute optical oscillator strengths for discrete and continuum photoabsorption of carbon monoxide (7–200 eV) and transition moments for the X 1Σ + → A 1Π system

Absolute optical oscillator strengths for the photoabsorption of carbon monoxide have been determined in the energy region 7–200 eV using low resolution dipole (e, e) spectroscopy and TRK sum-rule normalization. High resolution dipole (e, e) spectroscopy has been used to measure the absolute optical oscillator strengths for the photoabsorption of carbon monoxide in the valence shell discrete region from the first excitation threshold to 21 eV. Values of the absolute optical oscillator strengths for excitation of the vibrational levels of the A 1Π, C 1Σ +, B 1Σ + and E 1Π excited electronic states are reported. The variation of transition moment with internuclear distance is investigated for the vibronic bands of the X 1Σ + → A 1Π transition.

Absolute optical oscillator strengths for the photoabsorption of nitric oxide (5–30 eV) at high resolution

High resolution dipole (e, e) spectroscopy has been used to measure absolute optical oscillator strengths for the photoabsorption of nitric oxide in the valence shell region over the equivalent photon energy range 5–30 eV. Absolute optical oscillator strengths for the vibronic transitions of the γ(A 2Σ +-X 2Π), β(B 2Π-X 2Π), δ(C 2Π-X 2Π) and ϵ (D 2Σ +-X 2Π) systems have been obtained. The present results are compared with previously published experimental data and theoretical calculations.

Absolute optical oscillator strengths for the photoabsorption of molecular oxygen (5–30 eV) at high resolution

Absolute optical oscillator strengths for the photoabsorption of molecular oxygen in the valence shell discrete electronic excitation region have been measured in the energy range 5–30 eV using high resolution dipole (e, e) spectroscopy. Absolute intensities for the Schumann-Runge continuum region and for the discrete bands below the first ionization potential are reported and compared with available experimental and theoretical data.

Absolute optical oscillator strengths (11–20 eV) and transition moments for the photoabsorption of molecular hydrogen in the Lyman and Werner bands

The recently developed high resolution dipole (e, e) method has been used to measure the absolute optical oscillator strengths for discrete and continuum transitions for the photoabsorption of molecular hydrogen throughout the valence shell region, in the energy range 11–20 eV. Absolute optical oscillator strengths for the vibrational transitions of the Lyman and Werner bands are determined and compared with available experimental and theoretical data. The variation of the electronic transition moment with internuclear distance is studied for the Lyman and Werner bands. The present oscillator strengths and transition moments are in excellent agreement with the highest levels of theory. Finally the dipole strengths of both bands at the equilibrium internuclear distance (0.741 Å) are also reported.

Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution. III. The photoabsorption of argon, krypton, and xenon.

Absolute oscillator strengths for the photoabsorption of argon, krypton, and xenon in both the discrete and continuum regions have been measured. The results are compared where possible with previously published experimental and theoretical data. The present work is a continuation of recently reported measurements for helium [Chan et al., Phys. Rev. A 44, 186 (1991)] and neon [Chan et al., Phys. Rev. A 45, 1420 (1992)] obtained using the dipole (e,e) method at both low and high resolution. Using the low-resolution dipole (e,e) spectrometer [with a full width at half maximum (FWHM) of about 1 eV], absolute photoabsorption oscillator strength spectra for the valence and inner shells of argon, krypton, and xenon were obtained up to equivalent photon energies of 500, 380, and 398 eV, respectively. The high-resolution dipole (e,e) spectrometer (FWHM of 0.048 eV) was employed to obtain absolute photoabsorption oscillator strengths for the discrete electronic transitions from the ground states to the ${\mathit{ms}}^{2}$${\mathit{mp}}^{5}$ns and ${\mathit{ms}}^{2}$${\mathit{mp}}^{5}$nd ${(}^{2}$${\mathit{P}}_{3/2,1/2}$) manifolds where m=3, 4, and 5 for argon, krypton, and xenon, respectively. The absolute optical oscillator strength scales were obtained by single-point continuum normalization of the Bethe-Born converted electron-energy-loss spectra using the recently reported absolute optical data of Samson and Yin [J. Opt. Soc. Am. B 6, 2326 (1989)] for argon, krypton, and xenon atoms. High-resolution absolute photoabsorption oscillator strengths were also obtained in the energy regions of the autoionizing resonances corresponding to excitation of the inner-valence s electrons of argon, krypton, and xenon.

Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution. II. The photoabsorption of neon.

A recently developed high-resolution dipole (e,e) method [W. F. Chan, G. Cooper, and C. E. Brion, Phys. Rev. A 44, 186 (1991)] for the measurement of absolute optical oscillator strengths (cross sections) for electronic excitation of free atoms and molecules has now been applied to photoabsorption and photoionization processes for neon in the energy range 16--250 eV. The absolute scale is obtained by Thomas-Reiche-Kuhn (TRK) sum-rule normalization of the Bethe-Born converted electron-energy-loss spectrum. The measured absolute photoabsorption oscillator strengths for discrete electronic transitions of neon from the ground state to the 2${\mathit{s}}^{2}$2${\mathit{p}}^{5}$ns and 2${\mathit{s}}^{2}$2${\mathit{p}}^{5}$nd${(}^{2}$${\mathit{P}}_{3/2,1/2}$) manifolds are compared where previously reported experimental data are available. Measurements of the absolute optical strength in the photoionization continuum up to 250 eV are compared with other experimental and theoretical data. Absolute optical oscillator strengths in the 40--55-eV region of the 2s2${\mathit{p}}^{6}$np and 2${\mathit{s}}^{2}$2${\mathit{p}}^{4}$3lnl' autoionizing resonances are also reported.

Absolute optical oscillator strengths for the electronic excitation of atoms at high resolution: Experimental methods and measurements for helium.

An alternative method is described for the measurement of absolute optical oscillator strengths (cross sections) for electronic excitation of free atoms and molecules throughout the discrete region of the valence-shell spectrum at high energy resolution (full width at half maximum of 0.048 eV). The technique, utilizing the virtual-photon field of a fast electron inelastically scattered at negligible momentum transfer, avoids many of the difficulties associated with the various direct optical techniques that have traditionally been used for absolute optical oscillator strength measurements. The method is also free of the bandwidth (line saturation) effects that can seriously limit the accuracy of photoabsorption cross-section measurements for discrete transitions of narrow linewidth obtained using the Beer-Lambert law [${\mathit{I}}_{0}$/I=exp(nl${\mathrm{\ensuremath{\sigma}}}_{\mathit{p}}$)]. Since the line-saturation effects are not widely appreciated and are only usually considered in the context of peak heights, a detailed analysis of this problem is presented, with consideration of the integrated cross section (oscillator strength) over the profile of each discrete peak.The suitability of the high-resolution dipole (e,e) method for general application to atomic and molecular electronic spectra is evaluated by test measurements of the absolute dipole (optical) oscillator strengths for the photoexcitation and photoionization of helium, since for this atom detailed quantum-mechanical calculations using highly correlated wave functions have been reported. The absolute scale is obtained from the Thomas-Reiche-Kuhn sum-rule normalization of the Bethe-Born transformed electron-energy-loss spectrum and does not involve the difficult determinations of photon flux or target density. The measured dipole oscillator strengths for helium excitation (1 $^{1}$S\ensuremath{\rightarrow}n $^{1}$P, n=2--7) are in excellent quantitative agreement with the calculations reported by Schiff and Pekeris [Phys. Rev. 134, A368 (1964)] and by Fernley, Taylor, and Seaton [J. Phys. B 20, 6457 (1987)]. The absolute measurements are also compared with other experimental and theoretical oscillator strength determinations for photoexcitation and photoionization processes in helium up to 180 eV, including the 2snp and 3snp autoionizing resonances in the 59--72-eV energy region.