Photochemistry of acetylene at 1470 Å

Abstract

The photolysis of acetylene at 1470 Å has been studied over the pressure region from 13 to 1330 N m−2 (0.1 to 10 Torr). The quantum yield of diacetylene formation has been measured as a function of C2H2 pressure and the partial pressures of He and H2. The quantum yields of acetylene disappearance and of ethylene and hydrogen formation were also briefly studied. From these results it was concluded that the major primary photochemical process is direct dissociation C2H2 hν→C2H+H with a quantum yield of 0.3 and the process ot H2 production C2H2 hν→C2+H2 is minor (quantum yield?0.1). The remaining process is the formation of a metastable acetylene which reacts either with ground state acetylene to form C2H radicals or is deactivated by collisions with the walls or inert gases. The C2H radicals react with H2 130±11 times slower and with CH4 31±1.7 times slower than with C2H2. Absorption cross sections of diacetylene have been measured in the 1200 and 1800 Å region. The role of acetylene photolysis in the Jovian atmosphere is briefly discussed.