Activation and Decomposition of N2 on Heated Tungsten Filament Surfaces

Laser spectroscopic measurements showed that ground-state atomic nitrogen and vibrationally excited molecular nitrogen were produced by the contact of N2 with heated tungsten surfaces. The apparent activation energy for the production of N atoms was almost half of the N≡N bond dissociation energy. N-atom density increased in proportion to the square root of gas pressure below 100 Pa. These results suggest an equilibration between N2 and N. However, two-dimensional (2-D) modeling shows that the gas-phase production and loss of N atoms are unimportant. The experimental results were rationalized by 2-D modeling and a two-step gas-surface mechanism of N2 dissociation on hot filament surfaces. 2-D modeling returns N-atom distributions as a balance of N2 catalytic dissociation, the transport of N atoms, and loss of N on the reactor walls. However, the recombination processes of N atoms thus produced are not the real source of N2(v = 1), judging from the measured [N2(v = 1)]/[N2(v = 0)] population ratio.