Chemi-emission

Highly reactive species/defects which upon reaction, recombination, or annihilation give off localized energy to produce ejected electrons. In polymers, for example, bond breaking is known to produce free radicals which frequently must diffuse and react via second-order reactions. Chemical reactions at surfaces are known to be accompanied by electron emission (called chemi-emission)(23,24) via nonradiative electronic transitions. 

The chemi-emission mechanism for EE is accompanied by the release of an ion e.g., chemi-ionization. 

Production of the large quantihes of inorganic chemicals necessary for modern industrial processes can result in air pollutant emissions as undesirable by-products. Table 6-2 lists some of the more common inorganic chemi-... 

Fluorescent chemical sensors occupy nowadays a prominent place among the optical devices due to its superb sensitivity (just a single photon sometimes suffices for quantifying luminescence compared to detecting the intensity difference between two beams of light in absorption techniques), combined with the required selectivity that photo- or chemi-luminescence impart to the electronic excitation. This is due to the fact that the excitation and emission wavelengths can be selected from those of the absorption and luminescence bands of the luminophore molecule in addition, the emission kinetics and anisotropy features of the latter add specificity to luminescent measurements8 10. 

In order to show how the properties of the cavity can be used to develop a chemi-cal/biological sensor, the nature of sensor needs to be outlined. What is a sensor In simplistic terms, it is a device that is equipped with proper electronics to quantify changes in a given state of a system. It may be an accelerometer of an automobile, emission gas temperature of a jetliner, environment, bio-metabolism of living bodies, space storms, etc. What is required is a way to detect subtle changes. ... 

Figure 2.32 Principles of electron ionization source. Cathode (W, Re) e - emission e - energy is a function of accelerating voltage pressure (p) of gaseous sample <10 Pa. (H. Kienitz (ed.), Massenspek-trometrie (1968), Verlag Chemie, Weinheim. Reproduced by permisssion of Wiley-VCH.)...

The principal reaction discussed above forms oxygen molecules in high vibrational levels of the ground state. This is chemi-excitation but is not chemiluminescence vibration-rotation transitions of homonuclear molecules are forbidden. For such cases electronic absorption spectroscopy is the required technique. For reactions in which a heteronuclear diatomic (or a polyatomic) molecule is excited these transitions are allowed. They are overtones of the molecular transitions that occur in the near infrared. These excited products emit spontaneously. The reactions are chemiluminescent, their emission spectra may be obtained and analyzed in order to deduce the detailed course of the reaction. 

The mechanism of chemi-ionization and of CH( 4 2A) emission has been studied in considerable detail269,331 but it was not possible to decide on a unique mechanism for the emission process. Observed rotational distributions in the CH (A 2 A) state have been interpreted in terms of rotational relaxation270 but the uncertainty in the excitation mechanism renders such an enterprise somewhat ambiguous. 

Emission of the hydrocarbon flame bands, due to HCO, has recently been studied, along with chemi-ionization271. Again the mechanism is uncertain. 

Several other chromophores have been used in the development of sensors based upon ECL. For example, the luminol reaction is a conventional chemi-luminence reaction that has been studied in detail and it is believed that the mechanism of the ECL reaction is similar, if not identical, to that of the chemiluminescence. As shown in Fig. 2, the luminol ion undergoes a one-electron oxidation to yield a diazaquinone, which then reacts with peroxide or superoxide ( OOH) to give the excited 3-aminophthalate which has an emission maximum of 425 nm. This reaction is particularly versatile and has been utilized in a variety of ECL assays, many of which have been previously summarized by Knight [1], The luminol ECL reaction can be used for the determination of any species labeled with luminol derivatives, hydrogen peroxide, and other peroxides or enzymatic reactions that produce peroxides. A couple of examples are described later. 

Ministry of the Environment, Japan, 2004. Dioxin emission inventory English version http //www.env.go.jp/en/press/2005/1125a.html (inventory in 2004), Japanese version http //www.env.go.jp/chemi/dioxin/report.html... 

Furthermore, in the time interval surrounding the rather complex nucleation from the gas-phase products to solid matter, processes such as thermionic emission contribute to the ion concentration in such a way that the recombination of chemi-ions is not noticeable in the gross positive charge structure. The mechanism discussed above is, of course, only speculative, and it is based on ion-molecule reactions suggested by others (1,12). A more detailed picture of the particular ions involved must await mass spectrometric analysis. 

Brennan, M.C. and Svehla, G. (1989) Flow injection determination of boron, copper, molybdenum, tungsten and zinc in organic matrices with direct current plasma optical emission spectrometry, Fresenius Zeitschrift fur Analytische Chemie, 335, pp893-899. 

Laqua K. Optische Emissions-spektrometrie (1980) in Ullmann s Encyklopadie der technischen Chemie, Vol. 5. Verlag Chemie, Weinheim, 441-500. 

Analytical Method for the Determination of the Formaldehyde Emission from Chipboard related to the Concentration in Living Environments Methanol Chemie Nederland vof, Delfzijl (1982) Myers, G.E. Nagaoka, M. Forest Prod.J. 1981, 31(7), 39-44. Hoetjer, J.J. Holz als Roh- und Werkstoff 1981, 39(9), 391-393. 

Hoetjer, J.J. Experiences with measurements and analytic method for the determination of the formaldehyde emission from chipboard related to the concentration in living environments . Methanol Chemie Nederland vof Delfzijl 1982... 

Table IV. French Particleboard Production as a Function of Formaldehyde Emission (% of total Sales by CDF-Chemie).

Radio, chemi and thermoluminescence studies on polymers continues to attract much interest as an analytical probe. The t-irradiation of pyrene and naphthalene doped polyethylene gives excimer emission in the range of the high temperature radiothermoluminescence peak whereas other workers have used the technique to establish changes in the glass transition of the polymer 40 particular feature of radiothermoluminescence is... 

Variation of the light intensity at the emission maximum (507 nm) of lb with time recorded on the spectrofluorometer is shown in Fig. 2. The curve is a typical one for the chemi-1umi nescence of la-lc adsorbed on alumina. In a definite concentration of each sample, both the initial rate to attain the maximum of light intensity and the rate of disappearance from the maximum to become nearly zero decrease with the decrease in the activity of alumina by addition of a trace of... 

Terrestrial recovery is even more difficult to project than aquatic recovery. Given the life span of trees and the delay in the response of soil to decreases in acidic deposition, it is reasonable to suggest that decades will be required for affected trees on sensitive sites to recover once chemical conditions in the soil are restored. Overall, the timing and extent of chemi cal and biological recovery depend on how soon and how significantly emissions that cause acidic deposition are reduced. Moreover, human influences (e.g., land disturbance, introduction of exotic or invasive species), in addition to acidic deposition, can delay biological recovery after chemical recovery has occurred. 

The washed membrane is placed protein side up in the detection reagent and incubated for 5 min at room temperature, rotating by hand. The chemi-fluorescence signal is detected and quantified using the Typhoon 9400 variable mode imager (excitation 457 nm, emission filter 520BP40) and ImageQuant analysis software (Amersham Biosciences). 

BYK-P 4200 Stripping Agent to Reduce Odor and VOC Emissions in Polyolefin Compounds, supplier data sheet (09/2007). BYK-Chemie GmbH. 

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