Doppler broadening

About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.

Analysis of positron beam data by the combined use of the shape- and wing-parameters

Abstract: An improved approach is presented for the analysis of positron beam Doppler broadening data. Instead of analyzing the energy‐dependent shape parameter, the so‐called S(E) data, we combined the shape S(E) and wing W(E) data by plotting them as a trajectory in the S–W plane, using the implantation energy as a running parameter. It is shown that this plot is of particular interest for the qualitative interpretation of the data. Furthermore, it allows the independent determination of the characteristic shape and wing parameters of the different positron trapping layers without the use of a numerical simulation and fitting program. The method and its advantages and limitations are illustrated for three cases: a silicon sample implanted with helium, a metal–oxide–silicon system subjected to a bias voltage and a bare oxide layer on silicon.

Infrared Emissivity of Carbon Dioxide (4.3-μ Band)*

Abstract: Simplified equations are developed for computing the emissivity of the carbon dioxide 4.3-μ band. The harmonic oscillator model is assumed in computing band intensities, but anharmonicity is considered in computing the spectral distribution of emitted radiation. Calculated values of S¯/d and 2α012S¯12/d are presented for temperatures ranging from 300° to 3000°K, from which emissivities may be readily computed for a given pressure and optical path in both the weak-line and strong-line approximations. In the absence of significant Doppler broadening, both approximations provide upper limits to the emissivity. Emissivities are also computed for the case of a pure Doppler line shape for temperatures ranging from 300° to 1500°K. Doppler broadening is shown to be an important factor in setting a lower limit to the possible values of emissivity obtained at low pressures and long path lengths. Comparisons are made with published experimental data using the weak-line approximation; in several cases, the strong-line approximation as well as a mixed strong-line–weak-line approximation is also shown. The results of the present work are shown to be in good agreement with published experimental data and in definite disagreement with other theoretical calculations.

The XMM-Newton view of Mrk 3 and IXO 30

Abstract: We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2 galaxy, Mrk 3. We confirm that the source is dominated by a pure Compton reflection component and an iron Kα line, both produced as reflection from a Compton-thick torus, likely responsible also for the large column density (1.36 +0.03 0.04 × 10 24 cm 2 ) which is pierced by the primary powerlaw only at high energies. A low inclination angle and an iron underabundance of a factor ≃ 0.82, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron Kα line EW with respect to the Compton reflection component, being 610 +30 50 eV. Moreover, the iron line width, σ = 32 +13 14 eV, if interpreted in terms of Doppler broadening due to the Keplerian rotation of the torus, puts an estimate to the inner radius of the latter, r = 0.6 +1.3 0.3 sin 2 i pc. Finally, two different photoionised reflectors are needed to take into account a large number of soft X-ray emission lines from N, O, Ne, Mg, Si, Fe L and the Fe xxv emission line at 6.71 +0.03

High Resolution Measurements of Atomic and Molecular Lifetimes Using the High Frequency Deflection Technique

Abstract: The basic principles of the High Frequency Deflection (HFD) technique for the determination of atomic and molecular lifetimes as well as the first experimental tests were presented a couple of years ago In principle this technique is a further refinement of the conventional multichannel delayed coincidence technique with periodic electron excitation of free molecules The differences are mainly that the HFD technique utilizes a continuous electron beam from a high-power gun operating in the kilovolt range and that the periodic excitation is accomplished by sweeping the beam at an optimal rate, ie with a period equal to 3-10 times the lifetime to be studied With these two refinements the HFD technique enables lifetime measurements in all kinds of atoms, molecules, ions and ion-molecules with several orders of magnitude higher efficiency than other methods permit, thus opening possibilities for high resolution work in the absence of Doppler broadening Thus a number of lifetimes have been determined at a spectral resolution of 01 A FWHM or better, which is 20-50 times higher a resolution than what is normally achieved in lifetime measurements The variable sweep frequency and the multichannel registration make possible measurements over a large lifetime range (up to about 104 ns) which in turn offers unique possibilities for analysing multi-exponential decay curves With a time scale of arbitrary precision given by the sweep frequency, lifetime measurements have so far been performed with a total error down to 05% in favourable cases The HFD technique is now currently in use at this laboratory and several hundreds of lifetimes have been studied and reported in a number of publications In this paper we shall discuss more in detail the technique itself, its properties and possibilities compared to other methods for lifetime measurements A review of some of the experimental results obtained so far, with particular emphasis on abundance determinations of atoms and molecules of fundamental astrophysical interest, is also included as well as a critical discussion of given error limits in lifetime measurements in general