Measurement of Br photofragment orientation and alignment from HBr photodissociation: production of highly spin-polarized hydrogen atoms

The orientation and alignment of the (2)P(3/2) and (2)P(1/2) Br photofragments from the photodissociation of HBr is measured at 193 nm in terms of a(q) ((k))(p) parameters, using slice imaging. The A (1)Pi state is excited almost exclusively, and the measured a(q) ((k))(p) parameters and the spin-orbit branching ratio show that the dissociation proceeds predominantly via nonadiabatic transitions to the a (3)Pi and 1 (3)Sigma(+) states. Conservation of angular momentum shows that the electrons of the nascent H atom cofragments (recoiling parallel to the photolysis polarization) are highly spin polarized: about 100% for the Br((2)P(1/2)) channel, and 86% for the Br((2)P(3/2)) channel. A similar analysis is demonstrated for the photodissociation of HCl.     

The dynamics of the Cl+n-C4H10-->HCl (v',j') + C4H9 reaction at 0.32 eV

Rotational state resolved center-of-mass angular scattering and kinetic energy release distributions have been determined for the HCl (v' = 0, j' = 0-6) products of the reaction of chlorine with n-butane using the photon-initiated reaction technique, coupled with velocity-map ion imaging. The angular and kinetic energy release distributions derived from the ion images are very similar to those obtained previously for the Cl plus ethane reaction. The angular distributions are found to shift from forward scattering to more isotropic scattering with increasing HCl rotational excitation. The kinetic energy release distributions indicate that around 30% of the available energy is channeled into internal excitation of the butyl radical products. The data analysis also suggests that H-atom abstraction takes place from both primary and secondary carbon atom sites, with the primary site producing rotationally cold, forward scattered HCl (v' = 0) products, and the secondary site yielding more isotropically scattered HCl (v' = 0) possessing higher rotational excitation. The mechanisms leading to these two product channels are discussed in the light of the present findings, and in comparison with studies of other Cl plus alkane reactions.