Studies of reactions of atoms in a discharge-flow stirred reactor. Part 5.—O(3P)+ trimethylamine

Abstract

A discharge-flow system incorporating a stirred-flow reactor has been used to obtain stoichiometric coefficients for the rapid reaction between O(³P) and trimethylamine (TMA). The amounts of O atoms consumed and NO molecules produced when TMA was added to the stirred-flow reactor at 420 K were determined directly by measurements of chemiluminescent intensities. The yield of H atoms was estimated by a kinetic method when an excess of NO was present at relatively high pressures. On addition of CO to induce competition for OH between the reactions CO + OH → CO₂+ H (4) and O + OH → O₂+ H (5) the resultant decrease in O-atom consumption indicated that 5.2±1.4 OH radicals were generated per TMA molecule reacted. Reaction (5) is the only likely source of O₂ from the reaction. The stoichiometric equation deduced is (14.6±0.9)O+(CH₃)₃N → NO+3(CO+CO₂)+(7±1)H+(5.2±1.4)O₂ with the likelihood that a small yield of H₂ is generated also.

The stoichiometric coefficient of O atoms was found to decrease by 1.2±0.3 in O+N₂+CO systems when the point of addition of TMA was switched from the stirred-flow reactor to a section of the entry tubing, the times for reaction prior to observation changing from ca. 1 s (at 420 K) to ca. 15 ms (at 292 K) correspondingly. In view of the limited extent of possible reaction of formaldehyde in 15 ms this excludes formaldehyde and hence its precursor CH₃ radicals from being major intermediates in the reaction. The major reactions composing the mechanism have rate constants > 10⁹ dm³ mol^–1 s^–1 at 292 K.