Chemiluminescence and kinetic studies in O(3P)+ thiophene, pyrrole and furan mixtures

Abstract

Using fast-flow-discharge apparatus the reactions between oxygen atoms and thiophene, pyrrole and furan have been studied. Chemiluminescence has been observed from the electronically excited states of SO₂ and CH in thiophene + O(³P); NO, CH, CN and NO₂ in pyrrole + O(³P) and OH in furan + O(³P), and the evolution of its intensity has been monitored as a function of reactant concentration. Kinetic determinations have been done for the reaction of O(³P) and thiophene by following the SO^*₂ emission intensity and the O(³P) decay, using the titration of residual oxygen atoms with NO, at several temperatures, and for the reaction of O(³P) and pyrrole at 318 K by following the decay of O(³P) with NO. For the thiophene reaction, rate constants in the range T= 379–525 K can be fitted to the Arrhenius expression k=(1.6 ± 0.2)× 10¹² exp (–240 ±/RT) cm³ mol^–1 s^–1 and for the pyrrole reaction the value of the rate constant at 318 K is k=(2.8 ± 0.3)× 10¹² cm³ mol^–1 s^–1. Different reaction mechanisms are proposed in the light of the observed emissions and the empirical correlation existing between the kinetic parameters and the ionization potential of the aromatic hydrocarbons. A comparison is made with the reactions of O(³P) and benzene and O(³P) and pyridine.