Emission spectroscopy oxygen reactions

The participation in reaction of electronically excited oxygen molecules (in the X and A, states) has of late drawn much interest, and emission spectroscopy has played an important part in the identification and estimation of the singlet molecules. Hombeck and Herman observed the emission from the 02( X/- X )... 

Figure 3.1. Electrochemical behaviors of various noble metal electrodes in sulfuric acid [23-26]. (Graphs (a) (c) reprinted from Journal of Electroanatytical Chemistry, 35, Rand DAJ, Woods R, A study of the dissolution of platinum, palladium, rhodium and gold electrodes in 1 M sulphuric acid by cyclic voltammetry, 209-18, 1972 (b) reprinted from J Electroanal Chem, 55(3), Rand DAJ, Woods R, Cyclic voltammetric studies on iridium electrodes in sulphuric acid solutions nature of oxygen layer and metal dissolution, 375-81, 1974 (d) reprinted from J Electroanal Chem, 89(1), Michell D, Rand DAJ, Woods R, A study of ruthenium electrodes by cyclic voltammetry and X-ray emission spectroscopy, 11-27, 1978 (e) reprinted from J Electroanal Chem, 39(2), Capon A, Parsons R, The effect of strong acid on the reactions of hydrogen and oxygen on the noble metals. A study using cyclic voltammetry and a new teflon electrode holder, 275-86, 1972, all with permission from Elsevier.)...

Michell D, Rand DAJ, Woods R. A study of ruthenium electrodes by cyclic voltammetry and X-ray emission spectroscopy. J Electroanal Chem 1978 89(1) 11-27. Capon A, Parsons R. The effect of strong acid on the reactions of hydrogen and oxygen on the noble metals. A study using cyclic voltammetry and a new teflon electrode holder. J Electroanal Chem 1972 39(2) 275-86. 

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. 

In their work on the explosive oxidation of ammonia, which has already been discussed earlier, Husain and Norrish also examined the hydrazine system. Their principal results, obtained by the method of flash photolysis and kinetic spectroscopy, were as follows (a) no induction period was observed (b) NH emission, observable in the photolysis of pure N2H4, was visible at the shortest delay times (c) NO and OH were produced as the NH was decaying d) NO added to the hydrazine-oxygen system did not disappear in the combustion ( ) NO represented only about 5 % of the final products. Since, unlike the oxidation of ammonia, the major nitrogenous product is N2 rather than NO, Husain and Norrish concluded that reaction (15 ) is not a part of the main reaction sequence. They felt that the N-N bond was not split in in the main chain propagation. They proposed a mechanism involving nitrosamine, NH2NO, as a chain carrier viz. 

Automobile exhaust catalysts typically contain noble metals such as Pt, Pd and Rh with a ceria promoter supported on alumina. Traditionally, the principal function of the Rh is to control emissions of nitrogen oxides (NO ) by reaction with carbon monoxide, although the increasing use of Pd has been proposed. For example, recent X-ray absorption spectroscopy studies of Holies and Davis show that the average oxidation state of Pd was affected by gaseous environment with an average oxidation slate between 0 and +2 for a stoichiometric mixture of NO and CO. Exposure of Pd particles to NO resulted in the formation of chemisorbed oxygen and/or a surface oxide layer. 

Alkene Oxidation Reactions. The reaction of triethylsilane with ozone and use of the intermediate triethylsilyl hydrotrioxide in oxidation reactions have been described. Initial oxidation reactions reported included the formation of the 9,10-endoperoxide from 9,10-dimethylanthracene (eq 1), and an allyUc hydroperoxide from 2,3-dimethyl-2-butene (eq 2). Researchers also observed a near-IR emission from triethylsilyl hydrotrioxide as it decomposed at —60°C, consistent with generation of singlet oxygen. Other workers have characterized triethylsilyl hydrotrioxide by NMR spectroscopy and and measured the kinetics of its decomposition in deuterated acetone. ... 

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