Integrated Oscillator Strengths Research Articles

4d → 4f resonance in photoabsorption of cerium ion Ce3+ and endohedral cerium in fullerene complex

The theoretical investigation of the single-photoionization spectra in the 4d-resonance region (120–150 eV) for the ionic cerium Ce3+ and cerium in the endohedral complex (in practice, is presented. The fullerene cage is modeled by ab initio spherical jellium shell with an accurate account for the real distribution of carbon electron density. The oscillator strengths are calculated within the multiconfiguration Dirac–Fock (MCDF) approach for phototransitions from the outermost shells of the ion Ce3+ with and without the influence of the potential generated by a fullerene cage. It is shown that the integrated oscillator strengths have the main contribution from the Ce3+ 4d → 4f (ten possible from the phototransitions resonance photoexcitations. The corresponding precise MCDF values for the oscillator strengths and the transition energies are presented for the first time. It is demonstrated that the resonance oscillator strengths are slightly affected by the presence of the cage potential, despite the fact that the spectral levels structure is changed when the effect of this potential is included. The Auger 4d −1 decay from the cerium free ion Ce3+ and the encapsulated endohedral ion Ce3+@ are considered within the two-step model and the corresponding Lorentzian profiles are presented. This model clearly reveals the correspondence of the complex resonance profile in the Ce3+ photoabsorption to the fine structure of ion energy levels. The smoothing of the resonance profile in the photoabsorption of the endohedral system compared with the free ion Ce3+ is attributed to increasing the linewidths of the Auger transitions. This increase is estimated from the relevant experiment (Müller et al 2008 Phys. Rev. Lett. 101 133001) to be strong; as at least three times the value for an isolated ion. The presence of the confining fullerene cage decreases the autoionizing giant resonance lifetime for endohedral cerium in due to the opening of additional decay channels involving electrons of the fullerene shell, which cannot be accounted as a static potential. From consideration of the two-step model, it is clear that these processes are important. However, they lead only to broadening of the resonance. The dramatic reduction in the integrated oscillator strength in the cerium 4d resonance region can only occur when additional processes besides photoionization come into play.

New molecular descriptor of the “structure–property” model for the estimation of ionization potentials of naphtho- and anthraquinones

A two-parameter molecular descriptor is proposed in the QSPR model. It relates the ionization energies of molecules with topological indices and integrated oscillator strengths. Integrated oscillator strengths are obtained from electron spectroscopy data in the UV and visible spectral ranges. The regularities obtained are confirmed by the statistical processing of the data by multiple regression analysis methods in series of 1,4-naphthoquinone, 1-oxyanthraquinone, and 1-(4-tert-butylphenoxy)-9,10-anthraquinone derivatives.

Design of diethynyl porphyrin derivatives with high near infrared fluorescence quantum yields

A design strategy for (porphinato)zinc-based fluorophores that possess large near infrared fluorescence quantum yields is described. These fluorophores are based on a (5,15-diethynylporphinato)zinc(II) framework and feature symmetric donor or acceptor units appended at the meso-ethynyl positions via benzo[c][1,2,5]thiadiazole moieties. These (5,15-bis(benzo[c][1′,2′,5′]thiadiazol-4′-ylethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (4), (5,15-bis[4′-(N,N-dihexylamino) benzo[c][1′,2′,5′]thiadiazol-7′-ylethynyl]-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (5), (5,15-bis([7′-(4″-n-dodecyloxyphenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (6), (5,15-bis([7′-([7″-(4″ ′-n-dodecyloxyphenyl)benzo[c][1″,2″,5″]thiadiazol-4″-yl]ethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (7), 5,15-bis ([7′-(4″-N,N-dihexylaminophenylethynyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (8), and (5,15-bis([7′-(4″-N,N-dihexylaminophenylethenyl)benzo[c][1′,2′,5′]thiadiazol-4′-yl]ethynyl)-10,20-bis[2′,6′-bis(3″,3″-dimethyl-1″-butyloxy)phenyl]porphinato)zinc(II) (9) chromophores possess red-shifted absorption and emission bands that range between 650 and 750 nm that bear distinct similarities to those of the chlorophylls and structurally related molecules. Interestingly, the measured radiative decay rate constants for these emitters track with the integrated oscillator strengths of their respective x-polarized Q-band absorptions, and thus define an unusual family of high quantum yield near infrared fluorophores in which emission intensity is governed by a simple Strickler–Berg dependence.

Evaluation of electron impact excitation of N2 X 1Σg+(0) into the N2+ X 2Σg+(v), A 2Πu(v), and B 2Σu+(v) states

Published experimental integrated electric dipole photoionization oscillator strengths (fij) have been applied to the determination of absolute electron impact excitation cross sections of the N2 X 1Σg+(0) state into the N2+ X 2Σg+(v), A 2Πu(v), and B 2Σu+(v) states. The required relative electron impact cross section shape functions from threshold to energy values, limited by the imposition of relativistic effects at the high end, are established in this work by extracting accurate analytic functions from a critical review of extensive published experimental results. The cross sections examined here are important benchmarks used in establishing absolute values for critical rate processes in aeronomy. The determination of the absolute cross sections using the derived fij is accomplished through the physical relationship to a modified Born approximation analytic function that defines the electron impact shape functions. The zero order term of the analytic function is established in value relative to the remaining terms through shape analysis of the experimental electron impact results. The value of fij fixes the absolute value of the zero order term, determining the cross sections over the entire electron impact energy range. It is argued that this methodology is the most accurate approach at this time because of the existence of the intrinsically more accurate photometrically dermined fij. The critical quantities in atmospheric process applications are the branching ratios of excitation into the N2+ X 2Σg+, A 2Πu, and B 2Σu+ states. The N2+ (X 2Σg+, A 2Πu, B 2Σu+) partitioning within the total ionization cross section has been a source of disagreement in the literature, in spite of the fact that substantial effort has been expended in establishing acceptably accurate values. The present work establishes accurate cross sections for these states over the entire practical energy range required for research in atmospheric N2 physical chemistry. The accuracy of the results obtained here are verified by consistency with the most reliably established past experimental electron impact cross sections, in agreement with the independently established total N2+ cross section. We provide analytic collision strengths for the vibrational levels of the N2+ X 2Σg+, A 2Πu, and B 2Σu+ states, allowing establishment of rate coefficients for the system, at an estimated error ≤±8%.

Electron-impact multiple ionization of xenon ( σn+ , n=2–9)

Cross sections for production of multiple charged xenon ions (Xe n+ , n=2–9) by electron collision are presented in the 100–2500 eV impact energy range. We determinate the apparent ionization thresholds and the integrated oscillator strengths for the reactions. The present values are compared with available data from experimental groups using diverse techniques.

Electron impact ionisation cross section of krypton (σ n+ , n = 2–7)

Multiple ionisation cross section of krypton (Kr–Kr n+ , with n = 2,7) have been measured by time-of-flight spectrometry in the 100–3000 eV electron impact energy range. We determined the apparent ionisation thresholds and the integrated oscillator strengths for the reactions. The values are compared with data available in the literature.

Integrated oscillator strengths for multi-ionization processes under the Bethe-Born formulation

This work presents an empirical expression that allows one to estimate the integrated oscillator strength for multi-ionization of an atomic target reaction by electron impact as a function of the target final charge state. The individual ionization process is considered as a transition into the continuum and described through the Bethe formula. The results are compared with data for noble gases available in the literature.

Electron-impact ionization cross section of neon ( sigma n+, n=1-5)

Multiple ionization cross sections of neon (Ne-Nen+, with n=1-5) by electron impact have been measured with energies ranging from threshold up to 3000 eV, by a time-of-flight technique. A comparison with other experimental data is presented. The integrated oscillator strengths (Mn+2) for the processes have been determined showing a good agreement with previous reported data.

Soft X-ray photoabsorption of the NO dimer

X-ray absorption spectra are reported for the first time for the (NO)2 dimer at both the nitrogen and oxygen K edges, the data being obtained from (NO)2 multilayers formed on Ag{111}. The spectra display distinctive features which suggest an electronic structure for excited states of this species. Density functional theory studies of the core-hole excited states provide the basis for spectral assignments at the nitrogen K edge, allowing the identification of the N 1s electron promotion into the 2b1, 2a2, 7b2, 8a1 and 8b2 orbitals. Correlations are found between the experimental integrated oscillator strengths of the two π* states, at the nitrogen K edge, and the N-localized 2p coefficients of the unoccupied orbitals of the (1A1) state.

Electron impact multiple ionization cross section of argon (σ n+ , n = 3-6)

Multiple ionization cross sections of argon (ArAr n+ with n = 3-6) by electron impact have been measured with energies ranging from threshold up to 2000 eV, by a time-of-flight technique. A comparison with other experimental data is presented and discrepancies are discussed. The integrated oscillator strengths ( M n 2) for the processes have been determined showing good agreement with previously reported data.

The electronic absorption spectrum of NH 3 in the valence shell discrete and continuum regions. Absolute oscillator strengths for photoabsorption (5–200 eV)

The electronic spectrum and the absolute photoabsorption oscillator strengths (cross sections) for the valence shell of NH 3 have been measured using high- (0.048 eV fwhm) and low-resolution (≈ 1 eV fwhm) dipole (e, e) spectroscopy in the photon energy ranges 5.0–31 and 5.5–200 eV, respectively. The high-resolution data have been obtained at vibrational resolution and have been used to determine the integrated oscillator strengths of several vibronic transitions in the discrete absorption region below the first ionization potential. The oscillator strength data are compared with previously published absolute measurements obtained using direct optical techniques and electron impact spectroscopy. Criteria are discussed for estimating the corrections for Pauli-excluded transitions required for the normalization of relative photoabsorption spectra when using the partial Thomas-Reiche-Kuhn sum rule.

Charged-phonon absorption in doped C60.

We interpret the giant infrared resonances observed in ${\mathit{A}}_{6}$${\mathrm{C}}_{60}$ (A=K, Rb) by Fu et al. as being due to a classical charged-phonon effect in which the ${\mathit{T}}_{1\mathit{u}}$ molecular vibration modes of ${\mathrm{C}}_{60}$ acquire electronic oscilator strength via couplng to virtual ${\mathit{t}}_{1\mathit{u}}$\ensuremath{\rightarrow}${\mathit{t}}_{1\mathit{g}}$ electronic transitions. For the compounds ${\mathit{A}}_{\mathit{x}}$${\mathrm{C}}_{60}$ (x=3, 4, and 6), we predict, for weak electron--molecular-vibration coupling, that the softenings of the ${\mathit{T}}_{1\mathit{u}}$ modes are proportional to x, but that the integrated oscillator strengths of their absorption bands are proportional to the square of x.

Dipole properties, dispersion energy coefficients, and integrated oscillator strengths for SF6

Dipole oscillator strength distributions (DOSDs) have been constructed for ground SF6 including the IR, UV, and higher energy parts of the absorption spectrum. An adopted DOSD is used to evaluate the dipole oscillator strength sums Sk, k=2,1, 1/2 (− 1/2 )−3,−4,−6,..., mean excitation energies Ik, k=2(−1)−2, dipole–dipole dispersion energies for the interaction of SF6 with itself and with Li, N, O, H2, N2, O2, NO, H2O, NH3, CO2, CO, H, He, Ne Ar, Kr, and Xe, and the triple–dipole dispersion energy for (SF6)3. Pseudo-DOSDs have been constructed for SF6 which facilitate the evaluation of the dispersion energies involving SF6. In most cases uncertainties in our results for the dipole properties and dispersion energy coefficients are ≲1–3%.

Dipole oscillator strength distributions and properties for SO2, CS2, and OCS

Dipole oscillator strength distributions have been constructed and used to evaluate integrated oscillator strengths, and a variety of dipole oscillator strength properties, for ground state SO2, CS2, and OCS. Each distribution has been constructed by using experimental and theoretical photoabsorption cross sections and by subjecting the resulting dipole oscillator strength data to constraints provided by the Thomas–Reiche–Kuhn sum rule and molar refractivity data for the relevant dilute gases. The discussion includes graphical presentations of how various spectral regions of the dipole oscillator strength distributions contribute to the more important dipole properties.

Electron energy loss spectroscopy of acetone vapor

High resolution, inelastic electron scattering data can provide new spectroscopic information on the electronic structure of polyatomic molecules. Features in the acetone energy loss spectrum from 0 to 15 eV obtained for 100 eV incident electrons correspond to vibrational, electronic discrete, and electronic continuum excitations. These data are compared with optical measurements in a wide spectral region extending from the infrared to the vacuum ultraviolet. A comprehensive interpretation of the energy loss spectra is attempted with the use of photochemical and photoelectron data, as well as quantum-chemical calculations in the literature. Three Rydberg series with quantum defects of 1.03, 0.81, and 0.315 join onto bands previously discussed in terms of transitions to valence orbitals. These series converge to an ionization limit of 9.705 eV in good agreement with previous optical determinations. Dissociative continua underlie the Rydberg region and give rise to a variety of neutral products observed in recent photolysis work. Broad features in the ionization continuum appear to correlate generally with higher ionization potentials observed by photoelectron spectroscopy. Apparent oscillator strengths derived from the energy loss data for the bands at 4.4 and 6.35 eV and for a region (9.7–11.78 eV) of the ionization continuum agree very well with the photoabsorption measurements. Integrated oscillator strengths of 0.46 below 9.7 eV and 3.93 below 15 eV were derived from the electron impact data.

Photoionization and Absorption Spectrum of Formaldehyde in the Vacuum Ultraviolet

Absorption and photoionization coefficients have been measured for H2CO in the 600–2000-Å region. Integrated oscillator strengths were determined for a number of strong Rydberg transitions above 1200 Å. From the photoionization curve the first adiabatic ionization potential was found to be 10.87±0.01 eV. As an aid in interpreting the absorption spectrum, theoretical calculations were made using a single-configuration self-consistent field procedure for the Rydberg states and a model which included mixing between the Rydberg and valence states. On this basis, weak absorption features between 1340 and 1430 Å have been assigned to the B11(σ → π *) valence state. The 1A1(π → π *) valence state is deduced to be strongly autoionized just above the 2B2 ionization limit.