Gas-phase OH oxidation kinetics of pyrazine, pyrimidine, and pyridazine

The gas-phase kinetics of the OH-oxidation of three six-membered nitrogen heterocycles C4N2H4 isomers, namely pyrazine, pyrimidine, and pyridazine, were determined in a photochemical reactor coupled to a FTIR spectrometer and a SPME-GC/MS, at atmospheric pressure over the temperature range 298-353 K. Experiments were conducted using the relative rate method where two different references were employed for each studied compound. The obtained Arrhenius expressions are (in cm(3) molecule(-1) s(-1)) k(OH+pyrazine) (T) = (7.21 +/- 1.57) x 10(-13) exp(-(166 +/- 71) /T), k(OH+pyrazine) (T) = (1.18 +/- 0.57) x 10(-12) exp(-(362 +/- 155) /T), k(OH+pyrazine) (T) = (9.82 +/- 7.20) x 10(-12) exp(-(1063 +/- 248) /T), These results were compared with available literature data for other heterocyclic compounds and discussed in terms of structure-reactivity and temperature dependency. Their tropospheric lifetimes with respect to reaction with OH radicals were then calculated and found to be of the order of 29, 34, and 37 days for pyrazine, pyrimidine, and pyridazine, respectively.