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

Abstract Absolute quantum yields for primary H atom formation ( Φ H ) were measured under collision-free conditions for the room-temperature gas-phase dissociation of acetylene (C 2 H 2 ) 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-probe' technique. Using HCl and CH 4 photolysis at 193.3 and 121.6 nm, respectively, as a reference, values of Φ H (193.3 nm )=0.94±0.12 and Φ H (121.6 nm )=1.04±0.16 were obtained which demonstrate that for both photolysis wavelengths the H+C 2 H product channel dominates the primary C 2 H 2 photochemistry.