Enhancement and quenching effects of N(4S) and O(3P) atoms on nitric oxide β emission. Part 1.—The major effects

Abstract

In a discharge flow study, N(⁴S) and O(³P) have been shown to quench and enhance the intensities of NO β chemiluminescence associated with their combination. Rate constants of ∼1.5 × 10¹⁰ 1. mol^–1 s^–1 and (6.1 ± 0.6)× 10¹⁰ 1. mol^–1 s^–1 are obtained for direct removal of NO(B²Π) by N and O atoms respectively.

N is ∼80 times more efficient than N₂ in removal of precursors of NO(B²Π)(v′= 0,1) and (15 ± 3) times for (v′= 2,3), suggesting that each pair of levels has a different common precursor. O removes precursors of (v′= O)(11 ± 4) times more efficiently than N₂. These quenching effects on (v′= 0) emission are more and less pronounced in He and CO₂ carriers respectively, when the much greater variations of the O atom effect indicate that N and O do not act on one precursor only.

A considerable enhancement effect shows that O(³P) is ∼350 times more efficient than N₂ at 296 K in inducing crossing into NO(B²Π)(v′= 2), strongly supporting NO(b⁴∑–) as the immediate precursor. Unlike the quenching effects above, this enhancement is temperature dependent; at 196 K O is ∼1400 times more effective than N₂. Concurrent superimposed O atom quenching shows that collision induced crossing into NO(B²Π)(v′= 2) is a major depopulation route for the immediate precursor, which cannot be removed significantly by N atoms. CO₂ is more efficient than N₂ or He in inducing the crossing.