Electron-ion recombination in a dense molecular gas

A semi-quantal method is developed for treating the recombination of electrons and positive ions in a dense molecular gas. Extensive calculations are carried out relating to recombination in hydrogen, in nitrogen, in carbon dioxide and in damp mixtures of gases. This latter case is of special interest, recombination being greatly facilitated by the presence of quite a small amount of water vapour. A very high recombination coefficient is possible. For example in a nitrogen + hydrogen mixture which contains 20 % by volume of water vapour and which is at atmospheric pressure and at 2000 K the recombination coefficient is predicted to be between about 5.1 x 10-9 cm3 s-1 and 8.7 x 10-9 cm3 s-1: here the lower limit is calculated by the semi-quantal method assuming that the energy levels of the recombining system are hydrogenic while the upper limit is calculated by a purely classical method assuming that the energy levels of the recombining system form a continuum. Recombination coefficients have been deduced from measurements on the ionization in flames at atmospheric pressure. The values obtained lie satisfactorily between the predicted limits.