Microwave discharge, reactions

For stndying elementary reactions of importance in combnstion, a more controlled environment may be reqnired. Radicals or atoms may be generated by photolysis with UV radiation or with a microwave discharge on a snitable molecniar precursor. 

For example, a microwave discharge on H2 in an inert diluent, such as argon gas, is an efficient method for producing H atoms as reactants. Subsequent reaction of these H atoms with NO2 will yield OH and NO, and can serve as a useful source of hydroxyl radicals. These methods of reactant formation are well suited for experiments involving either static or flow reactor systems. 

Some time ago we synthesized the molecules Si02 and SiOS in solid rare gases. They are formed by the reaction of SiO or SiS with O atoms, generated by a microwave discharge. 

Indeed, access to matrix-isolated thioxoethenone C2OS (117) was gained by us in 1997.148 As proposed the photochemical addition of CS, generated by a microwave discharge in CS2, to CO was achieved by selective excitation (A. = 254 nm) of CS. This reaction could be reversed completely by changing the excitation wavelength to k = 313 nm. 

The reaction of CBr4 with potassium is reported to generate free C atoms and the rate constants for reaction with methane, ethylene, and benzene have been reported. The reaction of nitrogen atoms with CN radicals has also been used as a C atom source. Carbon atoms have also been produced by passing organics through a microwave discharge. ... 

Selective synthesis of acetylene (>90%) from methane was accomplished by microwave plasma reactions.568 Conversion of methane to acetylene by using direct current pulse discharge was performed under conditions of ambient temperature and atmospheric pressure.569 The selectivity of acetylene was >95% at methane conversion levels ranging from 16 to 52%. In this case oxygen was used to effectively remove deposited carbon and stabilize the state of discharge. Similar high... 

Branched acyclic alkanes also exhibit a slightly different behavior toward ozone on silica gel.105 Although tertiary alcohols are usually the main products, C—C bond cleavage to yield ketones always occurs and may become the predominant reaction. Atomic oxygen generated by microwave discharge of a C02/He mixture is a more selective reagent in the transformation of these compounds to tertiary alcohols.106... 

As an example of the reactions studied using this instrument we consider that between 0(3P) atoms and the CHF (X1 A ) radical [40], Atoms are formed in a microwave discharge of Q2/Ar, and CHF by IRMPD of... 

In a similar study, Phillips and Schiff345 found ki9 = 1.3 x 1010. As did Herron, they produced their atoms by a microwave discharge, and all their experiments were carried out at 298°K. Of particular interest in their work was the result that the nitrogen molecules produced in the reaction had sufficient energy to dissociate ozone i.e., more than 25.5 kcal/mole. Subsequent investigation showed that 75% of the molecular nitrogen was so energized.319-346... 

Figure 13. Cartesian [center-of-mass (CM)] contour diagrams for NH+ produced from reaction of N+ with H2. Numbers indicate relative product intensity corresponding to each contour. Direction of N+ reactant beam is 0° in center-of-mass system. For clarity, beam profiles have been displaced from their true positions (located by dots and 0°). Tip of velocity vector of center of mass with respect to laboratory system is located at origin of coordinate system (+). Scale for production velocities in center-of-mass system is shown at bottom left of each diagram (a) reactant N+ ions formed by impact of 160-eV electrons on N2 two components can be discerned, one approximately symmetric about the center of mass and the other ascribed to N+(IZ3), forward scattered with its maximum intensity near spectator stripping velocity (b) ground-state N+(3/>) reactant ions formed in a microwave discharge in N2. Only one feature is apparent—contours are nearly symmetric about center-of-mass velocity.12 ...

Dimethylsilanone (97) is also formed in the oxygenation of 95 with oxygen atoms generated by a microwave discharge of an Ar/02 stream and subsequent matrix isolation of the reaction products101. 

---