Exploring the spin–orbit reactivity in the simplest chlorine atom reaction

The reaction of Cl(2P)+H2→HCl+H serves as a benchmark for understanding the abstraction mechanism and has been the subject of numerous experimental and theoretical studies. Despite such intensive investigations, the reactivity of the low-lying spin–orbit excited Cl*(2P1/2) is unknown and has always been assumed to be negligibly small. By exploiting two different sources for generating the Cl(2P) beam, it is now found that the excited Cl*(2P1/2) atom is surprisingly more reactive to H2 than the ground state Cl(2P3/2) reagent, overturning conventional wisdom. By using a technique called Doppler-selected time of flight to directly map out the doubly differential cross sections (angle and speed), the detailed dynamical attributes for both spin–orbit states are also elucidated and contrasted for the first time for any bimolecular reaction.