Low Frequency Discharges

A more convenient way to achieve a plasma is with electrical energy, such as a low-frequency discharge. By increasing the electrical energy in a fixed amount of gas, all molecules are eventually dissociated and complete ionization is achieved. 

Electron Production Processes. The important electron production processes occur in the gas phase and, in the case of discharges with electrodes, at electrode surfaces. The major surface processes are (a) secondary electron emission on ion impact at the cathode, (b) field emission at sharp points on electrodes, and (c) thermionic emission in the case of arc-type discharges where electrodes become strongly heated. These are the sources of the primary electrons in d.c. and low frequency discharges. 

Low-temperature glow-discharges were utilized to cause bond rupture in hexafluoroethane (11). In these experiments, the power to support the discharge was supplied by a radio-frequency discharge that delivered 25 W of power, at a frequency of 8.6 MHz, to the copper coil surrounding the Pyrex reactor (see Fig. 2). The load coil was indue-... 

In Fig. 15.9, the impedance spectra of a freshly assembled Li/Cu5.5SiFe4Sni2S32 cell in discharge state and subsequent to it charging are shown. The spectrum is characterized by a high-frequency small semicircle followed by the low-frequency data in the form of an incomplete large semicircle. 

A number of hydrocarbon radicals having multiple bonds at the radical centre have also been trapped in inert matrices and studied by IR spectroscopy. Thus, ethynyl radical was obtained by vacuum UV photolysis (9) of matrix-isolated acetylene (Shepherd and Graham, 1987) as well as when acetylene and argon atoms excited in a microwave discharge were codeposited at 12 K (Jacox and Olson, 1987). An appearance of diacetylene bands was observed when the matrices were warmed up, while the absorptions of the radical C2H disappeared. Detailed isotopic studies of D-and C-labelled ethynyl radicals showed a surprisingly low frequency of the C=C bond stretching vibration at 1846 cm instead of c.2100cm for a true C=C triple bond (the band at 2104 cm was attributed to the... 

Nc is a function of reverse of frequency. In the low frequency region, most ions will arrive to the cathode in a half cycle of the discharge frequency. The low frequency was defined as follows,... 

It has been shown that a high frequency of modulation of the electrodeless discharge lamp (e g. 10 kHz) is advantageous. This frequency is well away from the low frequency of flame noise. If the amplifier is locked-in to this high frequency via a reference signal, an optimum signal-to-noise ratio is achieved. 

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