Site‐specific branching ratios for H‐atom production from primary haloalkanes photolyzed at 193, 222, and 248 nm

Selectively deuterated compounds are used to investigate the ‘‘site‐specific’’ nature of H‐atom production resulting from the photolysis of primary haloalkanes. The molecules investigated are 1‐iodopropane, 1‐bromopropane, iodoethane, bromoethane, and chloroethane, with photolysis being initiated at 193, 222, and 248 nm. Hydrogen and deuterium isotopes are systematically used to label chemically distinct carbon atoms within a given molecule. H‐ and D‐atom Doppler profiles are generated via two‐photon (121.6+364.7 nm) ionization resonant with Lyman‐α, and the relative H/D ratios are used to quantify the probability for hydrogen production from each carbon site. In general, photolysis of an intermediate, presumably the alkyl radical, is implicated as being a key step in the overall process. When using 248 nm radiation, the photolysis process is dominated by C–H (or C–D) bond cleavage at the β carbon position regardless of the system investigated. In contrast, results using 193 nm excitation display no obvio...