Sodium atoms, fluorescence

Figure 9.42 Intensity of sodium atom fluorescence as a function of time following excitation of Nal to the V potential with a pump wavelength of 307 nm (pulse duration ca 50 fs) and a probe wavelength of (a) 575 nm, (b) 580 nm, (c) 589 nm, and (d) 615 nm. (Reproduced, with permission, from Rose, T. S., Rosker, M. J. and Zewail, A. H., J. Chem. Phys., 91, 7415, 1989)...

The laser atomic fluorescence excitation and emission spectra of sodium in an air-acetylene flame are shown below. In the excitation spectrum, the laser (bandwidth = 0.03 nm) was scanned through various wavelengths while the detector monochromator (bandwidth = 1.6 nm) was held fixed near 589 nm. In the emission spectrum, the laser was fixed at 589.0 nm, and the detector monochromator wavelength was varied. Explain why the emission spectrum gives one broad band, whereas the excitation spectrum gives two sharp lines. How can the excitation linewidths be much narrower than the detector monochromator bandwidth ... 

Fluorescence excitation and emission spectra of the two sodium D lines in an air-acetylene flame, (a) In the excitation spectrum, the laser was scanned, (to) In the emission spectrum, the monochromator was scanned. The monochromator slit width was the same for both spectra. [From s. J. Weeks, H. Haraguchl, and J. D. Wlnefordner, Improvement of Detection Limits in Laser-Excited Atomic Fluorescence Flame Spectrometry," Anal. Chem. 1976t 50,360.]... 

A technique for the determination of methylmercury in aqueous samples (natural and seawater) involved the conversion of methylmercury to gaseous methyl-ethylmercury by reaction with sodium tetraethylborate (Bloom, 1989 Bloom and Watras, 1989). The volatile derivative was purged from the solution and concentrated on a graphitic column at room temperature. The derivative was thermally desorbed from the column, and then analysed by cryogenic gas chromatography with cold vapour atomic fluorescence detection. In addition to methylmercury, labile Hg11 species could be determined (as diethylmercury) as well as dimethylmercury (which is not ethylated). The detection limit for... 

C. Chen, J. Zhao, P. Zhang, Z. Chai, Speciation and subcellular location of Se-containing proteins in human liver studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and hydride generation-atomic fluorescence spectrometric detection, Anal. Bioanal. Chem., 372 (2002), 426-430. 

Supersonic expansions have been used to form small metal aggregates, (2 < n < 4). Emphasis is placed on the analysis of bound-free transitions in these small metal clusters. Discussion focuses on the characterization of variously produced sodium supersonic expansions and the analysis of laser Induced atomic fluorescence resulting from the photodissociation of triatomic sodium clusters. We will consider (1) the nature of observed "fluctuation" bands corresponding to bound-free transitions involving a repulsive excited state which dissociates to yield (Na-D line) sodium atoms and ground state,, ... 

In the course of similar experiments in which the liquid nitrogen baffle above is removed, an intriguing phenomena has been observed. We have been able to induce sodium D-line fluorescence upon single photon pumping at energies far lower than that required to simultaneously dissociate dimeric sodium and produce emission from excited atoms. The atomic fluorescence and its characterization will be the subject of our following discussion. Briefly, we have observed and characterized laser induced atomic fluorescence upon photodissocia-tlon of sodium trimers formed under a variety of conditions. 

Laser Induced Atomic Fluorescence and Sodium Trimer Fluctuation Bands... 

The dissociation energy of Na2 to two S sodium atoms is 6022 cm (AA). Therefore the photodissociation of dimeric sodium to produce the onset of D-llne fluorescence would require that Na2 possess 5500 cm of internal excitation (X Zg", v" A5). 

Technique HG = hydride generation AAS = atomic absorption spectrometry GF = graphite furnace AES = atomic emission spectrometry MS = mass spectrometry AFS = atomic fluorescence spectrometry ASV = anodic stripping voltammetry SDDC = sodium diethyl dithiocarbamate. Procedures ISO = Memational Standards Organization ISO/CD = ISO Committee Draft SM = Standard Methods ... 

When the extracted analytes provide no response on passing through a flow-cell located in a detector connected on-line to the continuous extractor via a dynamic manifold, the extractor outlet can also be connected to a manifold where the extract is merged with a stream of an appropriate reagent to derivatize the analytes as they are extracted, thereby enabling their subsequent on-line determination. This approach has been used to extract selenium from sand and sludge [57], and selenium, arsenic and mercury from coal. In the latter application, on-line derivatization with sodium tetrahydroborate (for selenium and arsenic) and tin chloride (for mercury) allowed the analytes to be determined in a direct manner using the atomic fluorescence technique [46]. 

Fig. 2 Chromatogram of a standard mixture after complexa-tion with sodium diethyldithiocarbamate. Composition of the standard mercury dichloride, methylmercury chloride, ethyl-mercury chloride, methoxyethylmercury chloride, ethoxyethyl-mercury chloride, phenylmercury chloride, and tolymercury chloride. [Reprinted from A. Knochel and H. Potgeter, Interfacing supercritical fluid chromatography with atomic fluorescence spectrometry for the determination of organomercury compounds,/. Chromatogr. A 786 192 (1997). Copyright 1997, with permission from Elsevier Science.]...

V.K.Bykhovski and E.E.Nikitin, Nonadiabatic transitions in atomic collisions. Quenching of sodium resonance fluorescence by aigon, Optika i Spektr. 17, 815 (1964)... 

The powerful technique of two-photon absorption, which permits limitations of Doppler broadening to be overcome (see Chapter 1), has been used in a study on sodium atoms in which the Stark effect in the 5s 2Si and 4d D and D levels was observed.188 The radiative lifetimes of the S and D Rydberg levels of Na,189 the use of laser-induced resonance fluorescence for the measurement of small concentrations of Na vapour,170 the quenching of Na(32P) and K(42P) by N2, 02, H2, and HaO,171 the chemi-ionization reactions of photoexcited atoms,172 and excitation of the K(42P ) level in collisions with rare-gas atoms173 have been the subjects of recent reports. 

Absorption and fluorescence methods arc theoretically less dependent on temperature because both measurements are made i>n initially unexdied atoms rather than thermally excited ones. In the example just considered, only about 0.0 7% of the sodium atoms were thermally e.xciied at 25(Xl K. Emission measurements are made on this tiny fraction of the analyte. On the other hand, ab.sorption and fluorescence measurements use Ihe 99.98% of the analyte present as unexcited sodium atoms to produce the analytical. signals. Note also that although a lO-K temperature change causes a 4% increase in excited atoms, the corresponding relative change in fraction of unexcited atoms is negligible. 

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