Photolysis of Propyne at 1470 Å

The photolysis of propyne (methylacetylene) has been examined at the 1470-Å Xe resonance line and at low pressures (0.2 torr) in order to minimize polymerization. The major products observed in decreasing order of importance are H2, C2H2, C2H6, and CH4. Evidence is presented for the occurrence of primary processes forming atomic and molecular hydrogen. The following are energetically possible at 1470 Å: CH3C≡CH+hΛ→C3H3+H →C3H2+H2 →C3H+H2+H →C3+2H2. The dominant process is atomic hydrogen formation via A. The formation of acetylene and ethane is attributed to the reaction sequence H+CH3C≡CH→CH3+C2H2, 2CH3→C2H6. This is consistent with the observation that the ratio of C2H2 to C2H6 is close to two and that, in the photolysis of CD3C≡CH, the acetylene is 75% C2H2 and the ethane is 95% C2D6.