The ultraviolet photochemistry of phenylacetylene was studied in a molecular beam at 193 nm. The only primary photofragments observed were HCCH (acetylene) and C6H4. Some of the C6H4 molecules were found to decompose to 1, 3, 5-hexatriyne and molecular hydrogen. An enthalpy of formation of Δ H f≤ 160±4 kcal mol-1 was determined for 1, 3, 5- hexatriyne from the energetic threshold for this process. This experimentally determined ...
