Oscillator Strength Data Research Articles

Reliable isotropic and anisotropic dipolar dispersion energies, evaluated using constrained dipole oscillator strength techniques, with application to interactions involving H2, N2, and the rare gases

Molecular dipole oscillator strength distributions (DOSDS), which are reliable in the sense of yielding accurate results for the various dipole properties of molecules, can be constructed if sufficient input information is available. The DOSDS are constructed from extensive experimental and theoretical information, including oscillator strength and photoabsorption cross section data, and are constrained to reproduce accurate refractivity measurements of the relevant dilute gases and to satisfy oscillator strength sum rules. The techniques for obtaining the DOSDS, and related properties, are well established for the evaluation of reliable isotropic dipolar dispersion energies. In this paper they are extended to the evaluation of anisotropic dipole properties, with particular emphasis on anisotropic dispersion energies. The approach used will be illustrated with applications involving H2, N2, and the rare gases. Also included will be brief discussions on (i) the use of reliable results for the dipole–dipole and triple–dipole dispersion energies in constructing complete two- and many-body potential energies and (ii) the advantages of constrained DOSD methods, relative to other approaches, for determining all the dipole properties of molecules.

The refractivity of helium and its measurement by laser interferometry

This article covers the historical background to the study of the helium atom by optical methods, and some essential results from the classical and quantum mechanical theory of optical dispersion. A simple undergraduate-level experiment, designed for refractivity measurements by cw laser interferometry, is described, and the ingredients of the theoretical calculation of the refractivity are discussed. It is shown that careful experimental work in this area can yield information that provides a valuable test of the accuracy and completeness of the available oscillator strength data.

Cross sections for the direct and dissociative ionisation of NH3, H2O and H2S by electron impact

The semi-empirical approach of Jain and Khare (1976-7) which uses oscillator strength data as input, has been utilised to obtain the first theoretical cross sections for the direct and dissociative ionisation of the NH3, H2O and H2S molecules by electron impact for energies varying from the ionisation threshold to 10 keV. The cross sections for the production of the major ions, namely NH3+, NH2+, H2O+, the minor ion OH+, and the total ionisation cross sections are in satisfactory agreement with a number of experimental values. For the minor ions NH+, O+ and H+, the theory underestimates the cross sections. For the ions produced by the ionisation of H2S no experimental results are available for comparison.

Reply to Comments of Bichsel et al. on "Mean excitation energy for the stopping power of metallic aluminum"

Replies are made to comments made by Bichsel et al. on the choice of inner-shell correction, experimental energy-loss-data set used, neglect of range data, and the relevance of current optical oscillator-strength data to the metallic Al I value.

Vacuum ultraviolet absorption spectrum of p-benzoquinone

The vacuum ultraviolet absorption spectrum of p-benzoquinone measured by photometric and photographic techniques is reported. The valence transitions are assigned and the Rydberg absorptions analysed showing that both p and d series are present. This observation is interpreted as showing that the highest occupied molecular orbital of the molecule is localised on the ketone groups and that molecular core structure has to be explicitly considered in accounting for the series. Oscillator strength data are reported and shown to support the ketonic character of the Rydberg series.

Integrated dipole oscillator strengths and dipole properties for Ne, Ar, Kr, Xe, HF, HCl, and HBr

Dipole oscillator strength distributions have been constructed, and used to evaluate integrated dipole oscillator strengths and a variety of dipole oscillator strength properties, for ground state Ne, Ar, Kr, Xe, HF, HCl, and HBr. 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 or related data for the relevant dilute gases. The resulting dipole properties are generally the most or only reliable values available for the hydrogen halides, for the rare gases they largely augment reliable results for most of the properties already available in the literature. The results for HCl are used to discuss an interesting molecular effect in the photoabsorption spectrum of this molecule betwen ~200 eV and ~205 eV.

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.

A search for interstellar H2O(+) in diffuse clouds

view Abstract Citations (11) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A search for interstellar H20+ in diffuse clouds. Smith, Wm. H. ; Schempp, W. V. ; Federman, S. R. Abstract Searches for H2O(+) toward HD 187982, Zeta Oph, O micron Per, and Zeta Per have yielded significant upper limits for H2O(+) when compared with existing models for similar lines of sight. Using available oscillator strength data, the column density for HD 187982, for example, cannot exceed 3 x 10 to the 12th per sq cm H2O(+) molecules. The most sensitive measurement for H2O(+) toward Zeta Oph is apparently limited by a blend with upper atmospheric H2O(+), which is also present in the HD 187982 spectrum. Publication: The Astrophysical Journal Pub Date: February 1984 DOI: 10.1086/161682 Bibcode: 1984ApJ...277..196S Keywords: Interstellar Matter; Molecular Clouds; Water; Absorption Spectra; Abundance; Atmospheric Moisture; Line Of Sight; Line Spectra; Oscillator Strengths; Astrophysics full text sources ADS | data products SIMBAD (5)

Dipole oscillator strength distributions and properties for methanol, ethanol, and n-propanol

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state methanol, ethanol, and n-propanol and used to evaluate integrated ("band") oscillator strengths and the dipole oscillator strength sums Sk and Lk (for a variety of k values) for these molecules. Each DOSD is constructed by using available experimental and theoretical photoabsorption cross sections and by constraining the resulting dipole oscillator strength data to satisfy the Thomas–Reiche–Kuhn sum rule and molar refractivity constraints. The discussion includes an analysis of the reliability of the results.

Dipole oscillator strength distributions and related properties for ethylene, propene and 1-butene

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state ethylene, propene, and 1-butene. Each DOSD is constructed by using available experimental and theoretical photoabsorption cross sections and by constraining the resulting dipole oscillator strength data to satisfy the Thomas – Reiche–Kuhn sum rule and molar refractivity constraints. The latter were obtained from experimental refractive index measurements of relevant dilute gases. The recommended DOSDs, and the values of integrated "band" oscillator strengths, and the dipole oscillator strength sums Sk and Lk (for a variety of k values) obtained from them, are reported. The discussion includes an analysis of the reliability of the results using 1-butene as a detailed model.

Molecular Rydberg transitions: Cyanogen chloride

The electronic absorption spectrum of cyanogen chloride has been investigated in the range 2200-1250 Å. The first s-Rydberg transitions, X ̃ 1 Σ + → 3 Π 1 and X ̃ 1 Σ + → 1 Π 1 have been assigned, and analyzed to yield exchange and spin-orbit coupling parameters. The relative intensities of these two transitions have been shown to accord with an intermediate coupling situation. The π → π ∗ intravalence excitations, leading to 1.3(Σ −, Δ and Σ +) states, have been discussed. It has been shown that one or both of the 1Σ − and 1Δ states have bent geometries and that the 1Σ + state is located (tentatively) at 79 755 cm −1. Two σ → π ∗ π → σ ∗ states have been assigned, one at 56 340 cm −1, the other at 74 450 cm −1. The latter assignment is tentative, being largely based on observed vibronic interferences between the X ̃ 1 Σ + → 1 Π 1 transition and the 74 450 cm −1 transition. A considerable amount of vibrational oscillator strength and quantum defect data is presented.

Dipole oscillator strength distributions and sums for C2H6, C3H8, n-C4H10, n-C5H12, n-C6H14, n-C7H16, and n-C8H18

Dipole oscillator strength distributions (DOSDs) have been constructed for ground state ethane, propane, n-butane, n-pentane, n-hexane, n-heptane, and n-octane. Each DOSD is constructed by using available experimental and theoretical photoabsorption cross sections and by constraining the resulting dipole oscillator strength data to satisfy the Thomas–Reiche–Kuhn sum rule and molar refractivity constraints. The latter were obtained using available experimental refractive index measurements of relevant dilute gases. The recommended DOSDs, and the values of integrated "band" oscillator strengths and the dipole oscillator strength sums Sk and Lk (for a variety of k values) obtained from them, are reported. The discussion includes an analysis of the accuracy of the results and a comparison with available literature values, which are scarce, for the dipole properties of the alkanes.

On the dissociation of nitrogen by electron impact and by E.U.V. photo-absorption

The dissociation of N 2 by electron impact and by e.u.v. photo-absorption is studied, and it is shown that the forbidden predissociation of the numerous 1Π u and 1Σ u + valence and Rydberg states of N 2 in the 11–24eV energy range is the dominant mechanism for N atom production. By measuring the absolute emission cross sections for the e.u.v. singlet bands of N 2 and by using the generalized oscillator strength data of Lassettre (1974), it has been possible to construct a detailed model of the total N 2 dissociation cross section which is in good agreement with the measurements of Winters (1966) and Niehaus (1967) and provides some insights into the maximum possible N( 2D) yield from dissociative excitation. The total cross section for exciting N 2 e.u.v. radiation in the 800Å–1100Å wavelength range has been measured and found to have a value of 3.4 ×10 −17 cm 2 at 100 eV under optically thin conditions. Although this result implies that large fluxes of e.u.v. photons should be excited in auroral substorms and in the airglow, they are not observed, and we show that this development is a consequence of radiation entrapment and predissociation. The total cross section for dissociating N 2 by electron impact is given for optically thin and thick media. And some questions concerning the energy budget of a magnetospheric storm which are raised by these results, are discussed.

Non-reversed source of Br atom resonance radiation and its application to the measurement of Br atom concentrations

Bromine atom resonance radiation, emitted following collisions of Br2 with Ar*3P2,0 metastable atoms, has been investigated. Depending on whether the excited Br atom emitters produced have been thermalised to room temperature, or are still translationally hot, Doppler and Biondi models for the Boltzmann or non-thermalised Br atom emitters can be used to interpret measurements of integrated absorption intensity as a function of Br 4p52P ground state atom concentration. Nuclear hyperfine splitting of the resonance transitions, which contributes to line broadening, was included in the models. The results show that, for the non-reversed Ar*+ Br2 resonance lamp, absorption intensity may be used to determine absolute Br atom concentrations with the use of the appropriate oscillator strength. Some new oscillator strength data for Br are reported. The measured Br atom resonance line oscillator strengths are shown to be insensitive to the translational kinetic energy of the Br emitter, because nuclear hyperfine splitting is the dominant line broadening mechanism at energies < 1 or 2 eV. The 157.7 and 131.7 nm resonance lines of Br are the most suitable for measurements of high (> 2 × 1013 cm–3) and low (< 3 × 1012 cm–3) concentrations of Br using the Ar*+ Br2 lamp.

A Model for Energy Deposition in Liquid Water

both a redistribution of oscillator strengths relative to the gas phase, and the possible existence of a collective oscillation (plasmon). We investigate the effects of such a plasmon on the partition of energy deposited by fast electrons. To accomplish this, we develop a heuristic model of the liquid based primarily upon the extensive body of gas phase generalized oscillator strength data. The model has one major free parameter, the strength of the 21.4 eV plasmon. Using standard resonance shapes to approximate the energy loss spectrum of the plasmon, we estimate that the water plasmon has an oscillator strength of 2 (+J about 0.6) and a half-width of about 3.5 eV. We then calculate the slowing down of an electron in liquid water according to continuous-slowing-down theory, and after allowing for plasmon decay, compare the yields for the liquid and gas phases. Our results indicate that when the plasmon decays by ionization it produces a spectrum of only subexcitation electrons. We find a modest change in the yields with the eV per-ion-pair lowered from 30.7 in the gas to 28.5 in the liquid.

Superexcited states of NH 3, H 2O and HF

Extending the method which was employed for CH 4, the energy spectra for photoabsorption and photoionization and those for excitation (including superexcitation) are calculated using ultraviolet photoelectron spectroscopy data for the respective molecules, NH 3, H 2O and HF, and oscillator strength data for their isoelectronic atom, Ne. A discussion of the classification of superexcited states is given. There are three possibilities for superexcitation: (1) that attributed to high-Rydberg states converging to the first ionization potential followed by a Jahn-Teller molecular distortion, (2) that attributed to excitation from inner orbitals, including both those cases followed by and those not followed by molecular distortion, and (3) that attributed to double excitation. From a comparison between calculations of the ionization efficiency curves and the experimental results, the present treatment is found to give reliable results.

Superexcited states of CH 4

The energy spectrum of a superexcited state (the different between the total photoabsorption and photoionization cross section) is calculated using ultraviolet photoelectron data for CH 4 and oscillator strength data for the iso-electronic atom, Ne. From this estimate we have concluded that the superexcited state of CH 4 is interpreted in terms of Jahn-Teller distortion of high Rydberg states referring to the 2T 2 state of CH + 4. The inconsistency between the data of the UV optical spectrum and results of other measurements or analyses is pointed out and discussed.

Variational calculations of long-range forces

The coefficients of the R-4, R-6 and R-8 terms in the series representation of the long-range interaction between two atomic systems at separation R are evaluated by a two-centre variational procedure, using highly refined ground-state wave functions. Calculations are carried out for all atom-atom and atom-ion pairs drawn from the one- and two-electron systems H, He+, He, Li+ and H-. The values for the R-6 coefficient are in excellent agreement with the values previously derived from oscillator strength data.