EPOXIDE FORMATION IN THE REACTIONS OF THE NITRATE RADICAL WITH 2,3-DIMETHYL-2-BUTENE, CIS-2-BUTENE AND TRANS-2-BUTENE AND ISOPRENE

Epoxide formation in the nighttime reaction of NO3 with 2,3-dimethyl-2-butene, cis- or trans-2-butene or isoprene was studied in a 480 l reaction chamber with in situ FTIR spectroscopy as analytical technique. Most experiments were carried out at either 20 Torr in argon or at 740 Torr in synthetic air. In the case of 2,3-dimethyl-2-butene the epoxide formation was studied in the range 20-740 Torr using either argon or air as diluent gas and its 02 dependence was studied in N2/02 MiXtures with O2 concentrations in the range 1.7 x 10(15)-4.9 x 10(18) molec cm-3, at a total pressure of 740 Torr. In the experiments performed at 20 Torr in argon, epoxides were found in all reactions as main products. The measured molar yields were 95.3% for 2,3-dimethyl-2-butene, 50% for cis- and frans-2-butene and 20% for isoprene. In the experiments performed at 740 Torr air, epoxides were below the detection limit in the case of cis- and trans-2-butene and isoprene, whereas a yield of 17.4% of the epoxide was measured in the 2,3-dimethyl-2-butene experiments. Possible reaction mechanisms explaining the experimental results are discussed.