H O Di Rocco

Spectrum of doubly ionized xenon (Xe III)

The spectrum of doubly ionized xenon has been investigated. The study is based on photographic recordings of xenon spectra in the 490-8900 A range. The number of classified lines has been increased from about 300 to about 1400. The lines have been classified as transitions between 73 even levels belonging to the 5s25p4, 5s25p36p, 4f, 5f and 5s05p6 configurations, and 83 odd levels belonging to the 5s5p5, 5s25p36s, 7s, 5d and 6d configurations. In particular, the classifications include most of the Xe III laser lines. The experimentally observed level structures are compared with the results of Hartree-Fock calculations and least-squares fits. A comparison is also made between the results of the present analysis and the published data on the Xe N4,5 OO Auger spectrum.

Stark Widths and Oscillator Strengths of Xe III Lines (Part II)

Stark widths and relative oscillator strengths were measured for more than 130 Xe III spectral lines emitted in a pulsed capillary discharge. As usual, these parameters become attainable once the deconvolution of line profiles is performed. In particular, 4f?6d, 5d?4f, 5d?6p, 6p?6d, 6p?7s and 6s?4f Xe III transitions have been considered. Extensive configuration interaction (CI) along with least-squares fitted atomic parameters were combined in Cowan code calculations, in order to check the quality of agreement with experimental f-values. Comparisons alike, drawn between experimental Stark widths and Griems semiempirical approach, guarantee an agreement within a factor of two for the whole of the lines, given a proper choice of the Gaunt factor for each single transition.

Stark widths and oscillator strengths of Xe III lines

In order to test the reliability of the Configuration Interaction (CI) method to predict the atomic parameters viz oscillator strengths of complex ions, we measured the profiles of forth (40) strong 6s-6p transitions of Xe III emitted by a pulsed capillary discharge. After deconvoluting the experimental shapes, Stark widths and relative oscillator strengths were obtained. When Least Square Fitted parameters were used in addition to extensive CI (CI + LSF), the agreement between theory and experiment for the gfs is within a factor two for the whole of the lines. Concerning the widths, the semiempirical approach provides values also within a factor two when the Gaunt factor is taken to be g(x) ~ 0.30.

Linewidths of singly charged, noble gas ions from Born and Born-Robb approximations: dependence with atomic parameters and electron density

The linewidths of the ns-np transitions (n = n0 + 1, n0 being the principal quantum number of the ground level) for the homologous sequence Ne II, Ar II, Kr II and Xe II, were calculated using analytical expressions for the cross-sections and rate coefficients. The data are in fair agreement with the experimental results, and a least squares fit to all theoretical values obtained, gives a relation betwen widths and atomic parameters Z and I −1 (where Z is the atomic number and I the ionization energy for the upper level) similar to the empirical dependence. On the other hand, analyzing the experimental results for the electron density N > 1017 cm−3, we show that there exists an empirical dependence between the width (w) and N given by w ∝ N 4/5. In both cases (theoretical and empirical), the atomic number and the inverse of the ionization potential, are relevant atomic parameters to describe linewidths. These can be represented by the empirical expression Z1/2w = AI −(3.0±0.1).

Experimental stark widths of xenon II spectral lines

Stark widths of many prominent 6s-6p and 5d-6p transitions have been measured and compared with theoretical results. A high current pinched discharge was used as a spectroscopic source. Electron density and temperature were estimated in 2.65 × 1022m−3 and 1.45 × 104 K respectively. Experimental Stark widths agree well with previous theoretical results. Our data are compared with those of other authors concerning to the homologous ions Ne II, Ar II, Kr II and Xe II.

RADIATIVE MECHANISMS IN LASER-PRODUCED PLASMAS IN Xe

Abstract In the present paper the LPP in Xenon at nearly atmospheric pressure is studied by frequency as well as temporal resolved spectroscopy. Experimental evidence confirms that the radiative recombination in the aftermath of the laser pulse, is the main mechanism by which the plasma dissipates its energy. It is also evident that the plasma observed is heated after the laser pulse ends, by a radiative wave evolving from the laser spot which also provides electrons. The evidence is supported by a careful analysis of the temporal evolution of ionized species, by the temporal evolution of the spectral shifts of the line spectrum and its spectral width, and by a careful analysis of the continuum emitted after the line spectrum in the plasma during the initial time-stage.

Diffuse reflectance optical topography: location of inclusions in 3D and detectability limits.

In the present contribution we investigate the images of CW diffusely reflected light for a point-like source, registered by a CCD camera imaging a turbid medium containing an absorbing lesion. We show that detection of μa variations (absorption anomalies) is achieved if images are normalized to background intensity. A theoretical analysis based on the diffusion approximation is presented to investigate the sensitivity and the limitations of our proposal and a novel procedure to find the location of the inclusions in 3D is given and tested. An analysis of the noise and its influence on the detection capabilities of our proposal is provided. Experimental results on phantoms are also given, supporting the proposed approach.

Non-LTE and optical depth effects to be considered in quantitative spectroscopy of cold and dense plasmas

Abstract This paper describes a collisional radiative steady state model for spatially homogeneous plasmas including an arbitrary number of levels of the ion to be considered. Non-equilibrium situations are taken into account as well as optical depth effects. Total particle density and temperature are used as independent parameters while the optical source thickness is obtained from the corresponding absorption coefficients. No particular case is assumed for the transitions considered and line intensities ratios can be obtained for any pair of allowed dipolar transitions. Temperature, particle and the derived electron densities ranges are considered which are of fundamental interest in quantitative spectroscopy (e.g. laser induced breakdown spectroscopy). Some well established results for simple cases are reproduced by the model and other results are presented for complex ions.

5s25p2(6p + 4f) configurations in triply ionized xenon (Xe IV)

The atomic-emission spectrum of triply ionized xenon (Xe IV) has been observed from 570 to 6900 A. The configurations 5s25p26p and 5s25p24f have been studied and we report 45 new energy level values for these configurations. As a consequence of this study one level 5s25p2(1D)5d 2G9/2 was also established. Six hundred and thirteen new lines have been classified as combinations between levels of the 5s5p4, 5s25p25d, 5s25p26s, 5s25p26p and 5s25p24f configurations. Least squares fitted parametric calculations involving configuration interactions have been carried out to interpret the observed spectrum.

Experimental and numerical study of a pulsed cold discharge

Pulsed-cold capillary discharges dominated by electron collisions are very useful for obtaining basic atomic data; furthermore laser action from several times ionized noble gases have been found using this type of discharge. In this work an experimental and numerical study is made such that the temporal behavior of the different ions and the electron density and temperature are in accordance with the experiments within 10-20%.