Kinetic evidence for the role of triplet states in a microwave discharge of ammonia

Abstract

A correlation has been found between the efficiency of certain additives in quenching the decomposition of ammonia in a microwave discharge and the energy of their lowest triplet states compared with that of ammonia. The variation of product yields with additive concentration follows the relationship expected from the competition NH^*₃ [graphic omitted] products, NH^*₃+ A [graphic omitted] NH₃+ A^*, where A is the additive and the asterisk denotes an excited state. Values of k₃/k₂ in the range of 10⁴ to 10⁶ l. mol^–1 have been obtained and these lead to a minimum lifetime for the excited ammonia molecule (NH^*₃) of 5 × 10^–6 s. The evidence is therefore that NH^*₃ is the first triplet state of ammonia. The difference between the effect of propylene on the discharge chemistry and radiation chemistry of ammonia can be rationalized in terms of the energies of the triplet and excited singlet ammonia molecules.