Activation in electric discharge

Fast electrons and, to a lesser extent, ions play in electric discharge the same part as do the photons in photochemical reactions. 

The activating effect of fast electrons implies that the transfer of electron energy in the collision of an electron with a molecule results in excitation of either the 

Two types of excitation functions are observed. An example is provided by earlier investigations [414]. Fig. 38 describes excitation functions of the 2655 A, 4 D2—2 and 2653 A, 4 Di—mercury lines. The former function rather slowly increases from the excitation energy E of the level 4 D2 and reaches a maximum at Epi which is much higher than E. The excitation function corresponding to the 2653 A line rapidly increases to a maximum of 2 —3 eV, and as rapidly decreases to a certain low value. 

The first function corresponds to the case in which the initial and final states of the excited particle (an Hg atom) have the same multiplicity (transition l So- 4 D) and the second to a process with multiplicity change (transition I Sq — 4 D). 

The absolute probability of excitation, namely the ratio of the number of effective electron collisions with a molecule to the total number of collisions, is equal to the ratio of effective to gas kinetic cross sections 

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