Oxygen excited atoms, characteristics, 72

The plasma-generated gaseous species are typically in electronically excited states. Figme 2a shows a typical optical emission spectrum of the Ar plasma produced in air (10). The characteristic emission peaks from the excited Ar molecules are clearly seen in the region from 696 nm to 812 tun. The peaks at 337 nm and 674 nm originate from the excited N2 molecule (11). The peak at 309 nm is due to the OH radical produced by dissociation of water vapor in the plasma (11). The peaks at 111 nm and 845 nm are due to the excited atomic oxygen. 

Production of ozone by irradiation or electric discharge in oxygen is readily revealed by the characteristic odor. The yield, though, is not easy to establish. In a closed system, it is very small in a flow system, it increases with the flow rate and decreases with the dose rate. These have been explained by taking the formation reaction as a three-body combination with O atom, O + 202— 03 + 02 (no chain), where the back reaction is indeed a chain process (Magee and Burton, 1951). In the mass spectrometer, 02+ is the main ion but the total yield of excited states is about the same as that of ionization (about 3.1), giving the following initial species ... 

The chromophores of vision are a unique set of polymethines, the Rhodonines, employing two atoms of Oxygen per molecule that are separated by a conjugated caibon chain. The resonance between these two molecules accounts for the specific absorption characteristics of the material. This absorption characteristic is not apparent until the absorption cross-section of the material is raised. This is accomplished by forming the material into the liquid crystalline state. In this state, the molecules are able to share their susceptibility to excitation. When excited, the... 

A study of the analogous reaction of O ( D ) with alcohols (Goldstein and Wiesenfeld, 1983), while of no direct atmospheric importance, reveals interesting details concerning the reactive characteristics of electronically excited oxygen atoms and provides information about the unimolecular dissociation dynamics of chemically activated molecules. In the generic case of O ( D2) reaction with methanol, a variety of reactive pathways are available ... 

On the other hand, the photoisomerization of oxazoles to isoxazoles involves not only the interchange of the 2 and 3 positions, but that of the 2 and 4 positions. To explain the latter reaction, the intervention of a Dewar compound was proposed (Scheme 13).41 The walk of the oxygen atom is characteristic of this mechanism. A quantum mechanical calculation suggested that the O—C-2 bond was weak (for the azirin) and the bond order between C-2 and C-5 was high (for the Dewar intermediate) in the excited state. 

The use of electron beam transparent samples facilitates the interpretation of the EDX result. In such thin foils, the self-absorption of the outgoing X-ray and secondary fluorescence can be ignored except for the very soft X-rays such as those produced by excited oxygen atoms. Hence the intensity of characteristic X-rays produced per incident electron is directly given by the formula... 

X-ray Fluorescence and Energy-Dispersive X-ray Analyses In x-ray fluorescence methods the elements in the samples are excited by absorption of the primary beam, and they emit their own characteristic fluorescence x-rays. These methods are widely used for the qualitative and quantitative determination of elements with atomic numbers greater than that of oxygen. In carbon surface science, XRF and EDX are used mainly to determine the inorganic constituents of carbons which either exist there as a result of activation method (e.g., phosphorus in phosphoric acid activated carbon), are present in the precursor [268] (Figure 2.13), or are deposited on the surface as a product of surface reactions [99], Quantitative determination of the content of elements in carbon using XRF is a difficult task, and a solid matrix requires special calibration procedure and special filters [269]. 

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