Excited Species in Flames

摘要: A finite resultant rate of chemical reaction in a system implies lack thermodynamic equilibrium, and therefore non-equilibrium distribution the various species over their accessible energy states. On molecular-kinetic basis, products encounters which reac­ tion has taken place are endowed with at least activation reverse reaction, must be shared for eqUilibrium to attained. In conventional "slow" such as hydrogen-iodine studied by Bodenstein, is slow compared attainment thermal equilibrium between degrees free­ dom concerned, only disequilibrium experimentally observable that total concentrations reacting species. If, however, sufficiently large, then departures from Maxwell­ Boltzmann become evident. The extent these depends on relative "relaxation times" exchange physical freedom-translational, rotational, vibrational, electronic. This article will concerned main electronic disequilibrium. development new techniques studying fast reactions, shock tube, flash photolysis, molecular beams, ultrasonics, revolutionized our capabilities observing systems not large (Le. concentration) disequilibrium, but also Along go careful studies oldest known way producing very rapid reactions-flames. bulk work discussed here relate premixed flames, rather than diffusion because former give more precise stratifi­ cation space phenomena, particularly when set up burner gives flat flame conical one. Such burners have been described Egerton & Thabet (1), Powling (2), Botha Spalding (3), Padley Sugden (4). stratification always limited, course, tendency towards differential different along dimension flow. effect, flames atmospheric pressure tend made "reaction zone" thicker 0.01 cm, major change occurs, merging into zone "burnt gas," final reactions full take place. latter may extend several centimeters. At lower pressures becomes correspondingly thicker. Across there is, gen­ eral, an increase temperature 1000 3000°C.