Source microwave discharge

Gorry P A and Grice R 1979 Microwave discharge source for the production of supersonic atom and free radical beams J. Rhys. E Sc/. 12 857-60... 

Microwave discharges at pressures below 1 Pa witli low collision frequencies can be generated in tlie presence of a magnetic field B where tlie electrons rotate witli tlie electron cyclotron frequency. In a magnetic field of 875 G tlie rotational motion of tlie electrons is in resonance witli tlie microwaves of 2.45 GHz. In such low-pressure electron cyclotron resonance plasma sources collisions between tlie atoms, molecules and ions are reduced and the fonnation of unwanted particles in tlie plasma volume ( dusty plasma ) is largely avoided. 

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. 

In a typical MIP-MS instrument, the ICP portion is replaced with one of a variety of microwave discharge sources, usually a fairly standardised (modified) Beenakker cavity connected to a microwave generator. The analytical MIP at intermediate power (<500 W) is a small and quiet plasma source compared with the ICP. The mass spectrometer needs no major modifications for it to be interfaced with the MIP. With MIP used as a spectroscopic radiation source, typically consisting of a capillary (1mm i.d.), a power of 30-50 W and a gas flow below 1 L min 1, multi-element determinations are possible. By applying electrodeposition on graphite electrodes, ultratrace element determinations are within reach, e.g. pg amounts of Hg. 

Baeva, M., Gier, H., Pott, A. et al. (2002) Pulsed microwave discharge at atmospheric pressure for NOx decomposition, Plasma Sources Sci. Technol. 11, 1-9. 

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. ... 

For industrial applications of excimer UV sources, the dielectric barrier and the microwave discharge are simple, reliable, and efficient excitation modes. There are a large number of vacuum UV (VUV), UV, and visible light transitions available. This allows a selective photoexcitation for many systems. Some sources of monochromatic UV light for industrial applications and their characteristics are in Table 2.1. 

Disilene and its isomer silylsilylene were neither available by standard vacuum flash pyrolysis of precursors 59-63, nor by the more elaborate method of pulsed flash pyrolysis of 60-63, a pulsed discharge in mixtures of argon and mono- and disilane74 or by the matrix photolysis of educts 59-66 using various light sources (Hg lamps, excimer laser)69,70,72, the microwave discharge in disilane 66 or the cocondensation of silicon atoms with SiFLt. 

Figure 1 Schematic of the atomic beam dosing source used with REMPI detection by Murphy et al. to study the recombination of H [36, 37] and N [38] at metal single crystal surfaces. A single crystal surface is supported on a manipulator in the path of a collimated molecular beam. The beam supplies reactant molecules or atoms, produced using a microwave discharge in the glass nozzle, which react and recombine at the surface. The reaction products are ionised by the laser, which is focused in front of the surface (inset), and the resulting ions are timed into a microchannel plate detector.

The spectral emission as a source of selective signal is also obtained by a microwave discharge, which constitutes the principle of the microwave emission detector [52]. 

Kaiser s studies employed a conventional spectrometer with A and B electric quadrupole fields, and by passing the HC1 gas through a microwave discharge situated prior to the molecular beam source, populations in the ratios 21 3 1 for the v = 0, I and 2 vibrational levels were obtained. An effusion source was operated at 170 K and line widths close to 1 kHz were obtained similar studies of DC1 were described, except that in this case the gas was preheated to 1440 K to produce increased vibrational excitation. Kaiser was able to observe spectra of H35C1 in J = 1, v = 0, 1,... 

The first successful application of molecular beam electric resonance to the study of a short-lived free radical was achieved by Meerts and Dymanus [142] in their study of OH. They were also able to report spectra of OD, SH and SD. Their electric resonance instrument was conventional except for a specially designed free radical source, in which OH radicals were produced by mixing H atoms, formed from a microwave discharge in H2, with N02 (or H2S in the case of SH radicals). In table 8.24 we present a complete A-doublet data set for OH, including the sets determined by Meerts and Dymanus, with J = 3/2 to 11/2 for the 2n3/2 state, and 1/2 to 9/2 for the 2ni/2 state. Notice that, for the lowest rotational level (7 = 3/2 in 2n3/2), the accuracy of the data is higher. These transitions were observed by ter Meulen and Dymanus [143], not by electric resonance methods, but by beam maser spectroscopy, with the intention of providing particularly accurate data for astronomical purposes. This is the moment for a small diversion into the world of beam maser spectroscopy. It has been applied to a large number of polyatomic molecules, but apparently OH is the only diatomic molecule to be studied by this method. 

Fig. 6. A flowing afterglow ion source used by Milligan et al. [42] in the study of the HJ+N reaction. Ions are generated by electron impact, or by the action of a microwave discharge...

Fig. 3. Schematic diagram of the guided ion beam tandem mass spectrometer, double octopole configuration. Pumping speeds are shown. Ion sources available are listed and the microwave discharge source is shown. Adapted from [9]...

Various routes have been used to generate matrix-isolated phosphorus oxide radicals, for example, PO2 and PO3. These are (i) codeposition of phosphine with O atoms from a microwave discharge source (ii) the matrix reaction of P2 (generated by heating GaP) and O3 (iii) laser ablation of P4O10 (iv) laser ablation of red P in a stream of O2. Both... 

Thermochemical data for alkyl amino radicals show for alkylhydrazines a trend in D (N-N) for these compounds in which the N-N bond was strengthened by increasing the degree of substitution by methyl in NH2 NH2 . From these values it was possible to determine values for the enthalpies of formation of the alkylamino radicals , and to confirm these by electron impact studies. The latter values were found to be in agreement with those obtained from pyrolysis studies. Hydrazine has often been used as a source of amino radicals by pyrolysis flame decomposition shock tube decomposition , electrodeless discharge and microwave discharge , viz. 

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