Studies of reactions of atoms in a discharge flow stirred reactor. Part 1.—The O + H2+ NO system

Abstract

The intensity of air afterglow chemiluminescence in N₂ carrier has been used to investigate the flow patterns within a diffusion-stirred flow reaction sphere with in-line and non-penetrating entry and exit tubings. Photometric measurements of intensities at entry and exit observation stations have been inter-calibrated under high linear flow rate conditions. Consequently rate constant data for O(³P) atom reactions are obtained directly from the relative entry and exit intensities measured under the diffusion-stirred flow operation of the sphere at lower volume flowrates.

Rate constants for H(²S) atoms are also measured, the latter generated in situ from O(³P) atoms by the reactions O + H₂→ OH + H (1), O + OH → O₂+ H, (2), using the air afterglow chemiluminescence associated with O + NO + M → NO₂+ M. (3), When NO is present in the O + H₂ system, the reaction H + NO + M → HNO + M (4), catalyses the removal of O atoms through the subsequent reaction O + HNO → OH + NO. (5), It is shown that k₅ > 100 k₆ for T⩽ 425 K where H + HNO → H₂+ NO. (6), Values of k₄ for M = Ar and N₂ in the range 360–425 K are measured; relative efficiencies of N₂: Ar =(1.64 ± 0.12): 1.0 are derived. No evidence for significant occurrence of reaction (7), OH + HNO → H₂O + NO (7), was found. An upper limit of k₇/k₅⩽ 4.4 is derived for T⩽ 425 K using literature limits for k₆ and k₇.

Arrhenius expressions k₁=(3.1 ± 0.5)× 10¹⁰ exp (–4950 ± 300 K/T) dm³ mol^–1 s^–1(363 K < T < 490 K) and k₃=(1.8 ± 0.5)× 10⁹ exp (+900 ± 85 K/T) dm⁶ mol^–2 s^–1(M = N₂)(285 K < T < 432 K) were also obtained, together with a relative efficiency of N₂: Ar =(1.62 ± 0.14): 1.0 in reaction (3), all in good agreement with the literature.