Kinetics of dissociative recombination of H3O+ ions with free electrons in premixed flames

Mass-spectrometric measurements have been made of the axial concentrations of the positive ions along premixed, flat flames of H-2, O-2 and N-2, either with or without trace amounts of acetylene added to the unburned gases. In each case the principal positive ion is H3O+, whereas the sole negatively charged species is the free electron. The main reaction governing the concentration of H3O+ in the burned gases of such a flame without acetylene added is: H3O+ + e(-) reversible arrow H + H + OH However, with acetylene in the burner supplies, chemi-ionisation in a flame's reaction zone produces amounts of H3O+ far in excess of those for equilibrium. Thus H3O+ disappears via the forward step of (1) in the burned gases, enabling its rate constant to be measured between 1820 and 2400 K. This ion-electron recombination coefficient was found to vary with temperature, T, according to: k(1) = (3.6 +/- 0.5) T--21+0.7 ion(-1) ml s(-1). The magnitude of k(1) at 2000 K is (4.2 +/- 0.6) x 10(-7) ion(-1) ml s(-1): theoretical considerations indicate that k(1) is proportional to T--1.5.