Flame photometric determinations of diffusion coefficients. Part 3.—Results for nitric oxide

The point-source technique for measuring gas-phase diffusion coefficients has been tested using trace quantities of nitric oxide diffusing in the burnt gases of atmospheric pressure flames of H2+ O2+ N2. The air afterglow emission was used to monitor concentrations of nitric oxide. The results validate quantitatively the technique, and diffusion coefficients for nitric oxide have been measured over the temperature range 1920–2520 K. These data can be accounted for with either a Lennard-Jones (12: 6) potential or a purely repulsive inverse power potential function to describe interactions of a nitric oxide molecule with those of the principal flame species. A slight preference for the second potential function is indicated. With the Lennard-Jones function it is not possible to arrive at one unique pair of force constants for NO. However, either σ= 3.60 × 10–10 m and (Iµ/k)= 85 K or σ= 3.58 × 10–10 m and (Iµ/k)= 91 K can be used to calculate diffusion coefficients with reasonable accuracy. For the other potential function, repulsive forces varying inversely with separation to the 12th power fit the measured diffusion coefficients best. Values of the corresponding force constants are given.