Rate coefficients for the gas‐phase reaction of isoprene with NO 3 and NO 2

Rate coefficients for the gas‐phase reaction of isoprene with nitrate radicals and with nitrogen dioxide were determined. A Teflon collapsible chamber with solid phase micro extraction (SPME) for sampling and gas chromatography with flame ionization detection (GC/FID) and a glass reactor with long‐path FTIR spectroscopy were used to study the NO 3 radical reaction using the relative rate technique with trans ‐2‐butene and 2‐buten‐1‐ol (crotyl alcohol) as reference compounds. The rate coefficients obtained are k(isoprene + NO 3 ) = (5.3 ± 0.2) × 10 −13 and k(isoprene + NO 3 ) = (7.3 ± 0.9) × 10 −13 for the reference compounds trans ‐2‐butene and 2‐buten‐1‐ol, respectively. The NO 2 reaction was studied using the glass reactor and FTIR spectroscopy under pseudo‐first‐order reaction conditions with both isoprene and NO 2 in excess over the other reactant. The obtained rate coefficient was k(isoprene + NO 2 ) = (1.15 ± 0.08) × 10 −19 . The apparent rate coefficient for the isoprene and NO 2 reaction in air when NO 2 decay was followed was (1.5 ± 0.2) × 10 −19 . The discrepancy is explained by the fast formation of peroxy nitrates. Nitro‐ and nitrito‐substituted isoprene and isoprene‐peroxynitrate were tentatively identified products from this reaction. All experiments were conducted at room temperature and at atmospheric pressure in nitrogen or synthetic air. All rate coefficients are in units of cm 3 molecule −1 s −1 , and the errors are three standard deviations from a linear least square analyses of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 57–65, 2005