Photodissociation dynamics of allene at 157 nm

The photodissociation dynamics of allene at 157 nm have been investigated u sing photofragment translational spectroscopy (PTS). Detection of the H and H-2 photoproducts, along with their heavy partner fragments, allows an acc urate assessment of the dynamics of the main photochemical processes. Three major channels have been identified: C-H bond fission, H-2 elimination, an d methylene formation (CH2+C2H2). The translational energy distribution of the C-H bond fission process indicates that there is little or no reverse b arrier for the dissociation pathway and that the dissociation is rather sta tistical in nature. The translational energy distribution for the H-2 elimi nation processes is peaked at similar to 18 kcal mol(-1), and covers a broa d range in energy, indicating that there is a sizable reverse barrier for t his process, which is typical of molecular hydrogen elimination in hydrocar bon molecules. The translational energy distribution for the CH2 formation process is peaked at similar to 8 kcal mol(-1), and also covers a wide rang e of energy, indicating that the process likely has a small reverse barrier . The relative yields for the H, H-2 and CH2 formation processes are determ ined to be 1:0.15:0.27.