H-atom elimination of $n$-propyl and \textit{iso}-propyl radicals: a photodissociation study*

The H-atom elimination channels in the UV photodissociation of jet-cooled $n$-propyl and \textit{iso}-propyl radicals are studied in the region of 237 nm using the high-$n$ Rydberg-atom time-of-flight technique. Upon excitation to the 3$p$ state by the UV photolysis radiation, $n$-propyl radical and \textit{iso}-propyl radical dissociate into the H atom and propene products. The product center-of-mass translational energy release of both $n$-propyl and \textit{iso}-propyl radicals have bimodal distributions. The H-atom product angular distribution in $n$-propyl is anisotropic (with \textit{$\beta $} $\sim $ 0.5), and that in \textit{iso}-propyl is isotropic. The overall average translational energy release is $\langle $E$_{T}\rangle $ $\sim $ 0.27E$_{avail}$ for $n$-propyl and $\langle $E$_{T}\rangle \quad \sim $ 0.21E$_{avail}$ for \textit{iso}-propyl. The bimodal translational energy distributions indicate two dissociation pathways: (i) a unimolecular dissociation pathway from the ground-state propyl after internal conversion from the 3$p$ state, and (ii) a repulsive pathway directly connected with the excited state of the propyl radical. Isotope labeling has also been carried out. The possible photodissociation mechanisms will be discussed.