Abstract
H 2 dissociation on polycrystalline tungsten is measured from 1700 to 3000 K using the filament temperature ( T) change and a normalized H-atom density at the chamber surface. The dissociation probability per H 2 filament collision ( P diss) saturates at 0.40 at high T and has a 2.25 ± 0.05 eV apparent activation energy when P diss ≪ 1. This activation energy is consistent with prior data and models, but the H 2 pressure dependence is not. P diss is independent of the H 2 pressure for this entire T range and the 1–85 mTorr pressure range studied, contradicting the primary model that has been used to explain H 2 dissociation on tungsten and other metals. We show that some apparently contradictory prior measurements are actually consistent with our observations and with each other, once this pressure dependence of P diss is recognized.
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