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Jos A.C. Broekaert. Analytic Atomic Spectroscopy with Flames and Plasmas (Wiley-VCH,2001)(ISBN 3527301461)(375s)_Ch_.pdf |
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Size 2.2Mb Date Dec 22, 2004 |
Index counter electrode 124, 127 coupling 7 crater diameter 251 crater pro®le 145 rf discharge 146 crater 133, 246 depth 134 diameter 133 critical concentration ratio 224 cross-contamination 130 cross-¯ow nebulizer 227 cross section 8, 297 crossed polarizers 183 crossed-dispersion 206 crossed-dispersion mode 59 cryocooling 285 cryopump 84 CsCl 213 Cu a Zn alloy 268 current-carrying plasma 235 current modulated 156 current ± voltage characteristic 137, 141, 142 cuvette 165, 173 Czerny ± Turner monochromator 199 D2 -lamp technique 178 Daly ± Multiplier 277 dark current 45, 65 data acquisition and treatment 84 dc arc 10 stabilized 212 dc arc spectrography 213 dc discharge 124 dc glow discharge with a ¯at cathode 244 dead time 81 Debye length 83 decay function 109 degassing 285 degeneracy 196 degree of dissociation 160 degree of ionization 20, 257 densitometer 62, 63, 254 departure from LTE 226 depression 164 depth-pro®le 248, 287 depth-pro®le analysis 246 depth-pro®ling analysis of steel 287 depth resolution 287 desolvate 104 desolvation 267 membrane 103 detecter noise 148 detection phase-sensitive 294 detection limit 182, 184, 201, 218, 223, 235, 237, 238, 243, 263, 277, 295, 296 ¯ame AAS 163, 169 furnace AAS 169 detection of the halogen 243 detector spectral response 13 determination sequential 202 simultaneous 202 deuterium lamp technique 177 diatomic molecule 26 diraction angle 207 diraction order 209 diusion 167, 242 diusion coecient 167 digestion under resistance heating 186 diode 66 diode AAS 149 diode array 70 diode-array 66 diode laser 154 diode laser atomic absorption spectrometry 176, see also diode laser AAS dipole 186 direct compact sample analysis 302 direct insertion probe 279 direct sample insertion 89, 228, 229 direct solids nebulizer 126 direct solids sampling 114, 117, 170, 174, 230, 268 discharge 2, 141 dielectric barrier (db) 281 electrodeless 235 hollow cathode 279, 295 restricted 136 dc 135 rf 135 single-electrode 235 spark 127 diuse spark 127 discharge gap 213 discharge lamp a ¯oating anode tube 141 ¯at cathode 141 discharge parameter 141 discharge under reduced pressure 11, 31, 135, 152, 297 discharges under reduced pressure 177, 294 discrete sampling 99, 161, 222 dispenser 165 dispersive element 52...
Index Rydberg constant 4 Rydberg state 298, 301 semi-quantitative analysis 254 semi-transparent mirror 151 sensitivity 85, 86, 184, 300 sequential 222 serum 187 Seya ± Namioka mounting 61 sheathing gas 218 shock wave 83 SiC 123, 285, 303, see silicon carbide side-on 221 side-on observation 29 sieve 303 sieving 302 sifter 125 s-component 179, 180 signal depression 84, 261 signal enhancement 84, 261 signal generation 88 signal-to-background 116 signal-to-background ratio 112 signal-to-noise 66 signal-to-noise ratio 44, 47, 59, 69, 293 silicon ± boron ± carbo ± nitride 225 Silsbee focussing 140 Simplex optimization 223 simultaneous 222 simultaneous detection 75 simultaneous emission spectrometer 194 single beam 150 single-channel instrument 151 SIT vidicon 204 Skewedness and excess test 48 skimmer 83, 255 cone 279 potential 279 slag 189 slit entrance 196 exit 196 slope 37 slurry 95, 114, 120 slurry atomization 120, 174 slurry nebulization 95, 268 slurry sampling 188 small sample 99 Smith ± Hieftje technique 182 SNR value 101, see signal-to-noise ratio soft plasma 272 soil 285, 286 solid sample 211 solid state detector photodiode array 67 SIT vidicon system 67...
The basic processes in optical atomic spectrometry involve the outer electrons of the atomic species and therefore its possibilities and limitations can be well understood from the theory of atomic structure itself. On the other hand, the availability of optical spectra was decisive in the development of the theory of atomic structure and even for the discovery of a series of elements. With the study of the relationship between the wavelengths of the chemical elements in the mid-19th century a fundament was obtained for the relationship between the atomic structure and the optical line emission spectra of the elements. In 1885 Balmer published that for a series of atomic lines of hydrogen a relationship between the wavelengths could be found and described as: l k Á n 2 a n 2 À 4 where n 2Y 3Y 4Y F F F for the lines Ha Y Hb Y Hg etc. Eq. (1) can also be written in wavenumbers as: n H 1al R 1a2 2 À 1an 2 2 1...
l is the orbital quantum number and has values of: 0Y 1Y F F F Y n À 1. The elliptical orbits can take on dierent orientations with respect to an external electric or magnetic ®eld and the projections on the direction of the ®eld also are quantitized and given by : L z ha 2pm l 9...
1.1 Atomic structure
Fig. 1. Atomic energy level diagram for the sodium atom. (Reprinted with permission from Ref. [3].)...
ne is the electron number density, A, B and B H are the Einstein transition probabilities for spontaneous emission, stimulated emission and absorption and ae Y aY b e and b are functions of the cross sections for the respective processes as well as of the velocity distribution of the particles involved. rn is the radiation density ( frequency n). When the system is in so-called thermodynamic equilibrium, the neutrals and the electrons have the same Maxwell velocity distribution and at a temperature T we have: nq an0 aab ae ab e B H a Aarn B gq ag0 Á exp ÀEq akT 25...
Here nq is the inverse value of the mean lifetime of the excited state q. For levels in which a decay by an allowed radiative transition can take place the lifetime is of the order of 10À8 s. When no radiative transitions are allowed we have metastable levels (e.g. Ar 11.5 and 11.7 eV), which only can decay by collisions. Therefore, such levels in the case of low pressure discharges may have very long lifetimes (up to 10À1 s). In the case of the absorption of electromagnetic radiation with a frequency nqp and a radiation density rn, the number density of Nq increases as: dNq adt Bqp Á Nq Á nr 31...
where c is the velocity of light, n0 is the frequency of the line maximum, R is the gas constant and M the atomic mass. The Doppler broadening thus strongly depends on the temperature. Accordingly, it is also often denoted as temperature broadening and re¯ects the kinetic energy of the radiating species (atoms, ions or molecules). The relevant temperature is denoted as the gas temperature or Doppler temperature. The measurement of the Doppler broadening thus allows the determination of the gas temperatures in spectroscopic sources (see line pro®les). For the light elements, the Doppler broadening is larger than it is for analytical lines with shorter wavelengths. For the Ca 422.6 nm line in the case of a hollow cathode discharge at a few mbar pressure, the Doppler broadening at 300 K for instance is 0.8 pm whereas at 2000 K it is 2 pm [13]. The Lorentzian broadening or pressure broadening results from the interaction between the emitting atoms of the element considered and atoms of other elements. The halfwidth is given by :
2 DnL 2ap Á sL Á N...
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