Absolute primary H atom quantum yield measurements in the 193.3 and 121.6 nm photodissociation of acetylene

Absolute quantum yields for primary H atom formation (ΦH) were measured under collision-free conditions for the room-temperature gas-phase dissociation of acetylene (C2H2) after photoexcitation at 193.3 nm and at the H-atom Lyman-α wavelength (121.6 nm) by a pulsed laser photolysis (LP)–laser-induced fluorescence (LIF) `pump-and-probeʹ technique. Using HCl and CH4 photolysis at 193.3 and 121.6 nm, respectively, as a reference, values of ΦH (193.3 nm)=0.94±0.12 and ΦH (121.6 nm)=1.04±0.16 were obtained which demonstrate that for both photolysis wavelengths the H+C2H product channel dominates the primary C2H2 photochemistry.