Absolute Oscillator Strengths Research Articles

Infrared Mn i laboratory oscillator strengths for the study of late type stars and ultracool dwarfs

Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 angstrom, 15 of which are in the infrared. The transitions at 12 899 angstrom and 12 975 angstrom are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 +/- 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 +/- 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 +/- 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150. (Less)

Lifetime measurements and transition probabilities in Mo II

Lifetimes have been measured using time-resolved laser-induced fluorescence for 16 odd levels in the doublet, quartet and sextet systems of Mo II, with energies in the range 48 000–61 000 cm−1. Absolute transition probabilities and oscillator strengths are determined for 110 UV and visible transitions (208 < λ < 485 nm) from a combination of experimental lifetimes and theoretical branching fractions. The theoretical results are obtained using the HFR method including core polarization effects.

Radiative lifetimes of NO A Σ2+(v′=,1,2) and the electronic transition moment of the A Σ2+−X Π2 system

Improved measurements of the radiative lifetimes of NO A Σ2+(v′=0,1,2) are presented and used to update the absolute electronic transition moment for the NO γ bands. The pressure-dependent fluorescence decay rate was measured in a low-pressure, room-temperature, flow cell containing dilute mixtures of NO in N2 using time-resolved laser-induced fluorescence excited with a picosecond laser and detected with a microchannel-plate photomultiplier tube. Fluorescence decay rates were determined using an analysis procedure that accounted for the electronic response of the detection system and measurement noise. Radiative lifetimes were determined from an extrapolation of the measured decay rates to zero pressure. In comparison with prior measurements of these radiative lifetimes, the improved experimental approach and analysis procedure result in a significant improvement in the measurement precision. The accuracy of the fluorescence decay-rate measurements was confirmed by independent measurements using time-correlated single-photon counting and time-resolved probing of laser-excited population in A Σ2+ using 266 nm photoionization and charge detection. The measured radiative lifetimes are 192.6±0.2 ns for v′=0, 186.2±0.4 ns for v′=1, and 179.4±0.7 ns for v′=2. The measured lifetimes are shown to be in outstanding agreement with those predicted by an electronic transition moment that is identical in form to the function recommended by Luque and Crosley [J. Chem. Phys. 111, 7405 (1999)] after appropriate rescaling. This rescaling does not affect the agreement of the transition moment function with the previously reported vibrational branching ratios and improves agreement with previously reported absolute oscillator strength measurements. Based on the rescaled transition moment, updated values of absolute transition probabilities in the NO A Σ2+−X Π2 system are presented.

Experimental oscillator strengths and hyperfine constants in Nb ii

We used high-resolution Fourier transform spectroscopy to measure new and improved transition probabilities and hyperfine data for singly ionized niobium. Intensity calibrated spectra were used to measure branching fractions of 145 Nb ii lines in the wavelength interval 2600–4600 A. Combining the branching fractions with previously reported lifetimes, absolute oscillator strengths for these 145 transitions were derived. In addition, line structures due to magnetic hyperfine interaction were studied resulting in new hyperfine splitting constants for 28 even and 24 odd energy levels.

Experimental oscillator strengths and hyperfine constants in Nb ii

We used high-resolution Fourier transform spectroscopy to measure new and improved transition probabilities and hyperfine data for singly ionized niobium. Intensity calibrated spectra were used to measure branching fractions of 145 Nb ii lines in the wavelength interval 2600–4600 A. Combining the branching fractions with previously reported lifetimes, absolute oscillator strengths for these 145 transitions were derived. In addition, line structures due to magnetic hyperfine interaction were studied resulting in new hyperfine splitting constants for 28 even and 24 odd energy levels.

Infrared atomic oscillator strengths for the study of brown dwarfs and extra solar planets

The spectral opacity of cool dwarf stars, brown dwarfs and extra solar planets peaks at infrared (IR) wavelengths and is dominated by neutral atoms and molecules. However, the laboratory database for atomic oscillator strengths is not complete and lacks experimental data, which is a source of uncertainty for atmospheric models of sub-solar objects. The aim of our new laboratory studies is to determine accurate absolute oscillator strengths and apply them to the study of sub-solar mass objects. Our technique uses high-resolution Fourier transform spectroscopy to measure accurate branching fractions for atomic transitions, which are combined with measured radiative level lifetimes to yield oscillator strengths. We discuss the status of the IR laboratory atomic database and our measurements for neutral species in the visible and IR.

Excitation Energies and Photoabsorption Oscillator Strengths of the Rydberg Series in CF3Cl. A Linear Response and Quantum Defect Study

Vertical excitation energies of the CF(3)Cl molecule have been obtained from a response function approach with a CC reference function to determine absolute photoabsorption oscillator strengths in the molecular-adapted quantum defect orbital formalism (MQDO). The present work covers more highly excited Rydberg states than have been experimentally reported. Assessing of the reliability of the present calculations is provided through a comparative analysis between the results of the molecule and the Cl atom. This can be used to allow for predictions of the same type of properties in other analogous systems.

Experimental Ti i oscillator strengths and their application to cool star analysis

We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465 to 3892 nm, 67 of which had no previous experimental values. Radiative lifetimes for thirteen energy levels, including the low energy levels 3d2 (3F) 4s4p (3P) z5Dj, have been measured using time resolved laser induced fluorescence. Intensity calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region lambda > 1000 nm, a region of particular interest to the analysis of cool stars and brown dwarfs.

Inner-shell excitation of gas phase carbonates and α,γ-dicarbonyl compounds

The inner-shell (C 1s, N 1s, O 1s) excitation spectra of dimethoxymethanone, diphenoxymethanone, and a series of α,γ-dicarbonyl compounds – 2,4-pentanedione, N-acetylacetamide, malonamide, acetyl anhydride, dimethyl malonate, diethyl malonate, 2-imidodicarbonic diamide, di- t-butyl iminodicarboxylate and dimethyldicarbonate – have been recorded in the gas phase with inner shell electron energy loss spectroscopy in the scattering regime dominated by electric dipole transitions. All spectra are presented on absolute oscillator strength intensity scales. They are interpreted with the aid of chemical series systematics and with the help of ab initio calculations. As found in a recent study of the X-ray absorption spectra of condensed carbonyl compounds [S.G. Urquhart, H. Ade, J. Phys. Chem. B 106 (2002) 8531], there is a very systematic correlation of the C 1 s → π C O ∗ transition energy and the relative oxidation at the carbonyl carbon, as expressed by a suitable oxidation index such as the sum of the atomic numbers or Pauling electronegativities of the elements bonded to the carbonyl carbon. Although the calculations clearly show there is delocalization between the two carbonyl groups, this had no detectible influence on the inner shell spectra. The absence of signals associated with π ∗ delocalization is explained in terms of core hole localization and symmetry effects.

Optical oscillator strengths for valence-shell and Br-3d inner-shell excitations of HCl and HBr

Absolute optical oscillator strength density spectra for valence-shell excitations of HCl and HBr, as well as for Br-3d inner-shell excitations of HBr, have been determined by high-resolution electron-energy-loss-spectroscopy method in the dipole limit. Absolute optical oscillator strengths for the discrete transitions of HCl and HBr are reported and compared with the previous results determined by the photoabsorption method.

Analysis of electron impact ionization properties of methane

Published experimental photon and electron impact ionization cross sections of CH4 have been reviewed and analyzed. Absolute partial ionization oscillator strengths (fij) for CH4+, CH3+, CH2+, CH+, H+, and H2+ have been obtained. Electron impact ionization cross sections are recommended based on agreement between the oscillator strength values derived from photoionization and electron impact measurements. Analytic functions for cross sections of CH4+, CH3+, CH2+, CH+, C+, H2+, and H+ produced by electron impact ionization of CH4 are established. The derived excitation cross‐section functions are accurate from threshold to impact energies limited by relativistic effects (i.e., E &lt; 0.2 MeV). The cross sections examined here are important for modeling Titan ionospheric chemistry.

Lower Rydberg series of methane: A combined coupled cluster linear response and molecular quantum defect orbital calculation

Vertical excitation energies as well as related absolute photoabsorption oscillator strength data are very scarce in the literature for methane. In this study, we have characterized the three existing series of low-lying Rydberg states of CH4 by computing coupled cluster linear response (CCLR) vertical excitation energies together with oscillator strengths in the molecular-adapted quantum defect orbital formalism from a distorted Cs geometry selected on the basis of outer valence green function calculations. The present work provides a wide range of data of excitation energies and absolute oscillator strengths which correspond to the Rydberg series converging to the three lower ionization potential values of the distorted methane molecule, in energy regions for which experimentally measured data appear to be unavailable.

The FERRUM project: improved experimental oscillator strengths in Cr II

We report absolute oscillator strengths for 119 Cr II transitions in the wavelength region 2050-4850 angstrom. The transition probabilities have been derived by combining radiative lifetimes, measured with time- resolved laser induced fluorescence, and branching fractions from intensity calibrated Fouirer transform spectrometer data. New radiative lifetimes for the 3d(4)(D-5)4p F-4, D-4 and P-6 terms are reported, adding up to a total of 25 energy levels with measured lifetimes used to derive this improved set of atomic data.

Superexcited states of carbon monoxide studied by fast-electron impact

Absolute optical oscillator strength density and double differential cross section spectra of CO below 120 eV are determined by fast electron impact. Some peaks above the first ionization threshold stand out as the momentum transfer square K2 increases. The doubly excited Rydberg states converging to C 2Σ+, D 2Π and F 2Π states of CO+, respectively, are confirmed in our spectra. Another peak at around 32 eV is assigned to the transition of (3σ)−1(2π)1 1Π← X1Σ+.

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.

Absolute oscillator strength densities below 100eV of N 2

The absolute optical oscillator strength density (OOSD) and generalized oscillator strength densities (GOSDs) below 100eV of N2 are determined with an incident electron energy of 2500eV and an energy resolution of 100 meV. The absolute generalized oscillator strengths (GOSs) for two transitions to the superexcited states at 23 and 31.4eV are determined and their momentum transfer dependence behaviours are discussed.

Inner-Shell Excitation Spectroscopy and X-ray Photoemission Electron Microscopy of Adhesion Promoters

The C 1s, Si 2p, Si 2s, and O 1s inner-shell excitation spectra of vinyltriethoxysilane, trimethylethoxysilane, and vinyltriacetoxysilane have been recorded by electron energy loss spectroscopy under scattering conditions dominated by electric dipole transitions. The spectra are converted to absolute optical oscillator strength scales and interpreted with the aid of ab initio calculations of the inner-shell excitation spectra of model compounds. Electron energy loss spectra recorded in a transmission electron microscope on partly cured adhesion promoter, atomic force micrographs, and images and X-ray absorption spectra from X-ray photoemission electron microscopy of as-spun and cured vinyltriacetoxysilane-based adhesion promoter films on silicon are presented. The use of these measurements in assisting chemistry studies of adhesion promoters for electronics applications is discussed.

Optical Oscillator Strengths of Hydrogen Bromide inthe 4.5–20 eV Excitation Energy Region

The absolute optical oscillator strength density spectrum of HBr in thevalence shell energy region of 4.5–20 eV has been determined by ahigh-resolution fast electron energy loss spectrometer. The opticaloscillator strengths for the broad a3Π+A1Π dissociation peak andthe discrete transitions of b 3Π1(ν′ = 0) and C1Π(ν′ = 0,1,2)are reported. It has been manifested clearly that the optical oscillatorstrengths of some transitions for the previous photoabsorption methodare subject to severe line-saturation effects.

Absolute differential cross sections for elastic and inelastic electron scattering from benzene with 1 kev impact energy

The absolute generalized oscillator strength and absolute inelastic differential cross section have been determined, as a function of the momentum transfer, for the 1E1u + 1B1u ← 1Ag transition in the benzene molecule. A previously described electron energy-loss spectrometer, featuring a Wien-filter velocity analyser, has been used. Employing 1000 eV incident electron energy and 1.0 eV energy resolution, absolute oscillator strength distribution as a function of electron energy loss was obtained in the 2–8° scattering angle range. The absolute elastic differential cross section was also determined spanning an angular range of 2°–14°. The photoabsorption spectrum converted from the electron energy-loss spectrum was compared with the interstellar extinction curve where we confirm the proportionality between the cross section and extinction.

Optical Oscillator Strengths of Hydrogen Chloride in theEnergy Region of 5.5–20 eV

Absolute optical oscillator strength density (OOSD) spectrum of HCl inthe valence shell energy region of 5.5–20 eV has been determined bythe high resolution fast electron energy loss spectrometer (EELS). Theoptical oscillator strengths for the broad A1Π+13Σ+dissociation peak and the discrete transitions of b3Π(ν′ = 0),C1Π(ν′ = 0,1,2) and M1Π(ν′ = 0) are reported.