Vacuum Ultraviolet Photolysis of Trimethylethylene

Abstract

The vacuum u.v. photolysis of trimethylethylene (2-methyl-2-butene) was carried out in a static system using rare gas resonance lamps: xenon (147.0 nm) and krypton (123.6 nm). The main hydrocarbon products were isoprene, 1,3-butadiene, propyne, allène, ethylene, and other minor products. Identification and measurements of the yields of hydrogen atoms, methyl, and ethyl radicals were carried out quantitatively by the use of radical–radical reactions. Because of the high yield of isoprene, the effect of conversion was studied. At a high conversion (i.e. 0.1%) the isoprene quantum yield decreases. Hydrogen atoms add mainly to the secondary carbon of the monomer (≥90%). The Δ(CH3,tert-C5H11) value was calculated to be 1.32 ± 0.14. With the krypton line (10.0 eV) no evidence was found for the participation of ionic reactions in the formation of the measured products except for the formation of 2-methyl-1-butene in a low yield. At this wavelength the ion quantum yield is 0.224 ± 0.005.