The role of predissociation states in the UV photooxidation of acetylene

We study the photo-induced oxidation of acetylene in two different spectral areas, around 220 and 320 nm. In both spectral areas, the dominant reaction pathways involve the rupture of the acetylene C−H bond, thus primarily generating C2H and H fragments. The released fragments react in O2 presence resulting in glyoxal and other molecular species formation. We observe strong variations in the photooxidation rates, which point to the increased participation of excited, predissociation states, in the oxidation process. Such effects of increased excited state participation in photooxidation should be observed in a variety of photo-induced reactions, affecting the reaction spectral response and eventually the reaction cycles in terrestrial or planetary environments.