Excited atom

If we expand Eq. (10-7) and simplify aeeording to the symmetry of the problem, (Richards and Cooper, 1983) the integral breaks up in the way it did for the helium atom excited state... 

As described above, this light comes partly from the formation of excited atoms and ions in the gas (Figure 6.3) and partly from their recombination with electrons (Figure 6.5). Unlike atom excitation, which mostly gives rise to light being emitted at one or two fixed wavelengths, the recombi-... 

If the electrodes are moved closer together, the positive column begins to shorten as it moves through the Faraday dark space because the ions and electrons within it have a shorter distance through which to diffuse. Near the cathode, however, the electric-field gradient becomes steeper and electrons from the cathode are accelerated more quickly. Thus atom excitation through collision with electrons occurs nearer and nearer to the cathode, and the cathode glow moves down toward the electrode. 

Just as for atoms, excited configurations of molecules are likely to give rise to more than one state. For example the excited configuration... 

Multiple-Bubble Sonoluminescence. The sonoluminescence of aqueous solutions has been often examined over the past thirty years. The spectmm of MBSL in water consists of a peak at 310 nm and a broad continuum throughout the visible region. An intensive study of aqueous MBSL was conducted by VerraH and Sehgal (35). The emission at 310 nm is from excited-state OH, but the continuum is difficult to interpret. MBSL from aqueous and alcohol solutions of many metal salts have been reported and are characterized by emission from metal atom excited states (36). 

The sensitivity, accuracy, and precision of solid-sample analysis have been greatly improved by coupling LA with ICP-OES-MS. The ablated species are transported by means of a carrier gas (usually argon) into the plasma torch. Further atomization, excitation, and ionization of the ablated species in the stationary hot plasma result in a dramatic increase in the sensitivity of the detection of radiation (LA-ICP-OES) or of the detection of ions (LA-ICP-MS). 

Table 21.1 Variation of atomic excitation with wavelength and with temperatnre...

Shore B. W. The Theory of Coherent Atomic Excitation, Vol. 2 (John Wiley, New York) (1990). 

Evidence has been advanced8 that the neutral helium molecule which gives rise to the helium bands is formed from one normal and one excited helium atom. Excitation of one atom leaves an unpaired Is electron which can then interact with the pair of Is electrons of the other atom to form a three-electron bond. The outer electron will not contribute very much to the bond forces, and will occupy any one of a large number of approximately hydrogen-like states, giving rise to a roughly hydrogenlike spectrum. The small influence of the outer electron is shown by the variation of the equilibrium intemuclear distance within only the narrow limits 1.05-1.13 A. for all of the more than 25 known states of the helium molecule. 

Mesospheric sodium atoms excited at the 3Ps/2 level scatter light in every direction. The backscattered beam observed at an auxiliary telescope B meters away from the main one looks like a plume strip with an angular length (p B 8h / where 8h stands for the thickness of the sodium layer. The tilt of the wavefront at the auxiliary telescope and vibrations equally affects the plume and the NGS. Thus departures of the plume from the average NGS location is due to the only tilt on the upward laser beam. Therefore measuring this departure allows us to know the actual location of the LGS, and to derive the tdt. Because of Earth rotation and of perspective effects, the auxiliary telescope has to track the diurnal rotation, and simultaneously to move on the ground to keep aligned the NGS and the LGS plume. Two mobile auxiliary telescopes are necessary for the two components of the tilt. 

Theoretical level populations. Sinee there are population variations on time seale shorter than some level lifetimes, a complete description of the excitation has been modeled solving optical Bloch equations Beacon model, Bellenger, 2002) at CEA. The model has been compared with a laboratory experiment set up at CEA/Saclay (Eig. 21). The reasonable discrepancy when both beams at 589 and 569 nm are phase modulated is very likely to spectral jitter, which is not modeled velocity classes of Na atoms excited at the intermediate level cannot be excited to the uppermost level because the spectral profile of the 569 nm beam does not match the peaks of that of the 589 nm beam. 

Fig. 18. UV-visible spectra of Agi,j.s/Ar mixtures (Ag Ar = 1 1(F) at 10-12K. Note the growth of Agj and Ag, clusters and loss of Ag atoms as a result of 305 nm, Ag atom excitation. Spectra A, B, and C represent irradiation times of 0,1, and 4 min, respectively (149).

A number of hydrocarbon radicals having multiple bonds at the radical centre have also been trapped in inert matrices and studied by IR spectroscopy. Thus, ethynyl radical was obtained by vacuum UV photolysis (9) of matrix-isolated acetylene (Shepherd and Graham, 1987) as well as when acetylene and argon atoms excited in a microwave discharge were codeposited at 12 K (Jacox and Olson, 1987). An appearance of diacetylene bands was observed when the matrices were warmed up, while the absorptions of the radical C2H disappeared. Detailed isotopic studies of D-and C-labelled ethynyl radicals showed a surprisingly low frequency of the C=C bond stretching vibration at 1846 cm instead of c.2100cm for a true C=C triple bond (the band at 2104 cm was attributed to the... 

A technique that utilizes a solid sample for light emission is spark emission spectroscopy. In this technique, a high voltage is used to excite a solid sample held in an electrode cup in such a way that when a spark is created with a nearby electrode, atomization, excitation, and emission occur and the emitted light is measured. Detection of what lines are emitted allows for qualitative analysis of the solid material. Detection of the intensity of the lines allows for quantitative analysis. 

Atomic fluorescence Light emitted by atoms excited by the absorption of light in a flame is measured Not a popular technique, but can offer sensitivity advantages... 

Fraction of atoms excited (Nx) solely depends upon the temperature of the flame (T), and... 

Therefore, the fraction of atoms excited critically depends on the temperature of the flame thereby emphasizing the vital importance of controlling the temperature in Flame Emission Spectroscopy (FES). 

A flame photometer (Figure 2.31) is designed to cause atomic excitation of the analyte and subsequently to measure the intensity of the emitted radiation. A monochromating system is essential to distinguish between the emission of the test element and other radiation from the flame. 

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