The nitrogen isotope mixing reaction catalysed by polycrystalline metal wires

Abstract

The velocity, k m , of the equilibration reaction 28 N 2 + 30 N 2 ⇌ 2 14 N 15 N over 0.47-50 Pa and 1133-1623K obeys the following kinetic laws, for polycrystalline wires, cleaned in ultra-high vacuum, of the metals stated: Re, k m = 1.1 x 10 20 p exp — (34/ RT ) molecules m -2 s -1 , W, k m = 3.2 x 10 25 p ½ exp — (153/ RT ) molecules m -2 s -1 , Mo, k m = 2.1 x 10 27 p ½ exp — (177/ RT ) molecules m -2 s -1 , where the units of T , R and p are K, kJ mol -1 K -1 and Pa respectively. An activated complex treatment in terms of partition functions gives reasonable agreement between theory and experiment for a mechanism for Re of molecular dissociation followed by atom recombination, and for W and Mo a reaction between atoms and molecules, possibly molecular radicals, competing for sites in the chemisorbed layer. The freedom of the activated complexes, relative to the respective adsorbed initial states, appears to decrease over Re > Mo > W.