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Swift, J. D. (1961) An investigation of the relation of the intensities of certain nitrogen bands to discharge parameters. Doctoral thesis, Northern Polytechnic.
The positive column of a pure nitrogen discharge has been investigated with the primary aim of determining the mechanism of production of nitrogen molecules in the as C 3Πυ excited state. Simultaneous measurements have been made of the energy distribution of the electrons in the column and of the intensities of certain bands in the Second Positive system of nitrogen.
The electron energy distribution has been investigated by means of a technique involving the determination of the second differential of a probe current vs potential characteristic. The various possible errors in the procedure are analysed in detail, and it is shown that the method is reliable under the conditions encountered in this work. The results show that two groups of electrons are present in generals (a) an electron swarm moving in equilibrium with the axial field in the column and having an energy distribution much 'peakier' than the Maxwellian form, (b) a high energy group reaching the column from the cathode region. A theory of the positive column has been developed and used in conjunction with the previous results to show that two stage ionisation processes are unimportant in the nitrogen positive column.
Expressions are derived for the intensity of a molecular band in the Second Positive system assuming that the C 3Πυ state is being populated (a) by a direct excitation mechanism, (b) by an indirect mechanism in which excitation of the singlet levels first occurs, followed by a collision of the second kind involving slow electrons. The band intensity measurements, which have been carried out using both photographic plate and photo-multiplier techniques, and the electron energy distribution results,are then used to determine which of the above mechanisms is the important one. The results indicate that the direct excitation mechanism predominates in the positive column of a pure nitrogen discharge.
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