Reaction with atomic oxygen, chemiluminescence

The relative and absolute intensities of chemiluminescence of Pb(C2H5)4 upon reaction with atomic oxygen under experimental conditions similar to those found in the upper atmosphere have been studied [65]. 

Glow. Chemiluminescent products formed in surface-assisted reactions involving atomic oxygen are believed to be a source of space vehicle glow, which may seriously interfere with the function of sensitive optical instruments designed to detect low light levels. The most widely accepted... 

Carbon suboxide is a linear symmetric molecule in its ground state and is of considerable Interest from a variety of viewpoints. Its electronic structure, for example, has been subjected to considerable theoretical analysis because of the extensive delocalized IT network. Because its constituent atoms are doubly bonded C and 0, it is the source of intensely chemiluminescent flames with atomic oxygen which have been shown to result in inverted distributions in product CO. The molecule has also been proposed as (i) a product of photochemical reactions in the primitive earth atmosphere, (il) a constituent of the Venus atmosphere, and (iii) a possible explanation for the variety of colors associated with the Mars surface. 

A report has appeared of the chemiluminescent gas-phase si lame-ozone system which incorporates a MO study supporting the conclusion that the importamt emitting species is H2SiO. Reaction of atomic oxygen with Me SiH has been investigated by... 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

The relative ease with which ozone loses one oxygen atom suggests that ozone might undergo reactions similar to those of O atoms under certain conditions. This was shown to be the case in the chemiluminescent reactions with NO, and now Halstead and Thrush have examined the reaction of O3 with SO and found a close relationship with the 0-1-SO reaction, analogous to the NO situation. 

The dioxiranone intermediate, which is formed in small amounts, reacts with the sensitizer to give singlet atomic oxygen and carbon dioxide the reaction of the singlet oxygen with the sensitizer is responsible for the chemiluminescence [1946]. 

TMDO inserts an oxygen atom into C-H bonds, with high selectivity in the order 3° > 2° > 1° bonds. The reaction is stereospecific with retention of configuration, and apparently occurs concertedly. ° As an example, c/5,c/i-l,3,5-trimethylcyclo-hexane (65) is oxidized cleanly to triaxial triol 66, and adamantane (67) is transformed to a mixture of bridgehead tetrol (68) and triol (69). The reaction with adamantane is accompanied by chemiluminescence, with triplet trifiuoroacetone El 75 kcal/mol) the apparent emitter. This observation constitutes further evidence that the oxygen atom transfer takes place concertedly. 

Motivated by this proposal, Sabbah et al. performed low temperature measurements of the rate coefficients for these reactions. 0( P) atoms were generated in the cold CRESU flow via 355 nm laser photolysis of NO2, and their concentration followed using chemiluminescence from excited NO2, formed in the association of 0( P) with NO, as a marker for the oxygen atom concentrations, which decayed exponentially as a result of reaction with the added alkene. Results were obtained in most cases down to 23 K or 27 K, except for the 0( P) + ethene reaction, for which only an upper limit to the rate coefficient could be measured at 39 K. 

Since the discovery of the Ba + chemiluminescence [16] it was found consistently in many reactions of metal atoms with halogen and oxygen containing molecules [1] that electronic product state distributions decrease monotonically with available energy in a manner suggesting qualitatively statistical behaviour and that the electronic inversions necessary for laser action [10] are elusive. QL yields for the reactions of ground state M S) are maximally a few percent (for Ca + I ) and more typically a fraction of a percent [1,17]. This is also typical for the reactions of metal atoms with the oxygen-donors O3, NO2 and N2O [1] and it is appropriate... 

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

The associative reaction of oxygen atoms with nitric oxide produces the yellow-green chemiluminescence in the air afterglow, easily seen by the naked eye. The reaction has long been used to measure the concentrations of O atoms in kinetics experiments [49-51] and is so bright that it has been used to visualize... 

It is important to note that the SO + O chemiluminescence reaction can be surface mediated in addition to occurring in the gas phase. Here, the oxygen atoms are weakly bound to the surface and react with SO diffusing to the surface ... 

In the low temperature reaction of oxygen atoms with acetylene at pressures in the torr range, chemiluminescent emission is observed from one or more electronically excited states of CO, CH, C2, OH and CHO. In none of these cases is the mechanism well established, so we will only mention briefly some recent work. 

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