Reduced electric field

Therefore, CO adsorbed on Cr3+ centers located on the (111) faces is expected to be characterized by somewhat higher frequencies. However, it has been shown for the (0001) face of a-Cr203 (where Cr3+ is in a very similar environment) that Cr3+ moves inward to a more shielded position upon relaxation, which leads to a reduced electric field strength at the chromium centers. Because of the stability of the surface complexes even at room temperature, it is not excluded that n backdonation may also play a role in the bond between the CO and the Cr3+ centers (which usually shift the CO frequency downwards). As discussed previously (see Section IV.A.4) the shift A v induced by increasing CO coverage is caused by lateral... 

The two electrons produced by the process axe accelerated by the electrical field and may ionise other gas molecules. An avalanche is formed. The frequency of the ionisation process is characterised by the first Townsend coefficient a. This coefficient depends on the reduced electrical field E/p, where p is the pressure of the gas. The increase dn of the n electrons after a distance dx is given by ... 

A and B are experimental constants that vary depending on the type of gas and, in general, also on the range of the reduced electrical field E/p (Table 2.3 and Fig. 2.8). 

Figure 2-3. Rate coefficients of ionization by direct electron impact in molecular gases (CO2, H2,N2-H2, CO) as a function of reduced electric field.

This ionization process corresponds to electronic excitation into a repulsive state of the ion, (AB+) , followed by a decay of this molecular ion. It is also illustrated by a vertical line in Fig. 2-2. One can see from Fig. 2-2 that the energy threshold for the dissociative ionization is essentially greater than that for the non-dissociative one. Data on the electron impact direct ionization for different molecular gases (CO2, H2, N2, etc.) are presented in Fig. 2-3 as a function of reduced electric field E/no, which is the ratio of the electric field over the neutral gas concentration. 

A semi-empirical relation for electronic excitation and ionization rate coefficients as a function of reduced electric field E/no was proposed by Kochetov et al. (1979) ... 

Calculate the relative increase of the electronic excitation rate coefficient of molecular nitrogen in a non-thermal discharge with reduced electric field, E/tio = 3 10 V cm, when the vibrational temperature is increased from room temperature to = 3000 K. 

Relation Between Electron Temperature and the Reduced Electric Field... 

The aforementioned EEDF permits one to correlate the reduced electric field and average electron energy, which is related to electron temperatrrre as (e> = l e, even for non-Maxwellian distributions. Such a relation can be derived, for example, from averaging the electron drift velocity in energy space (3 4) ... 

This relation is in good agreement with both Maxwell and Dmyvesteyn EEDFs. It is convenient to rewrite (3-58) as a relation between electron temperature and the reduced electric field... 

This linear relation between electron temperatnre and the reduced electric field is obviously only a qnalitative one. As one can see from Fig. 3-5, the relation T ) can be mote complicated in reality. 

If the reduced electric field in the plasma is not too high E/p < 10 V/cm Torr), the ion energy only slightly exceeds that of neutrals. At high electric fields (f/p 10 V/cm Torr), ion velocity, colhsion frequency v, and ion energy increase with electric field X is the ion mean free path) ... 

Combination of relations (4-4) and (4-5) gives formulas for calculating the breakdown voltage and breakdown reduced electric field as functions of an important similarity parameter pd ... 

Total transported charge 0.1-1 nC Reduced electric field Eln = (l-2)(E / )paschen... 

Reduced electric field EIria (V cm ) 4.8x10- 3x10- ... 

Maximum Current of Dark Discharge. Using (4-31), show that the maximum dark discharge current is proportional to the square of the gas pressure. Derive the relation between similarity parameters maximum current jmw.1 P -, ion mobility lJ.+p, reduced electric field E /p, and interelectrode distance pd. ... 

Figure 5-8. Rate coefficients as functions of reduced electric field (1) CO2 dissociation by direct electron impact (2) electronic excitation C0(2T E+) - CO(a n) (3) dissociative attachment of electrons to CO2 molecules. Solid lines correspond to calculations based on electron energy distribution functions in CO2 dashed lines, in CO.

Figure 5-9. Energy efficiency of carbon dioxide dissociation by means of electronic excitation of the molecules as functions of reduced electric field (1) contribution of singlet states (including...

Figure 5-29. (1) Reduced electric field E/ o and (2) ionization degree n /nt as functions of pressure in microwave discharge.

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