Signature of shape resonances on the differential cross sections of the S(1D)+H2 reaction

Shape resonances appear when the system is trapped in an internuclear potential well after tunneling through a barrier. They manifest as peaks in the collision energy dependence of the cross section (excitation function), and in many cases, their presence can be observed experimentally. High-resolution crossed-beam experiments on the S(D-1) + H-2(j = 0) reaction in the 0.81-8.5 meV collision energy range reaction revealed non-monotonic behavior and the presence of oscillations in the reaction cross section as a function of the collision energy, as predicted by quantum mechanical (QM) calculations. In this work, we have analyzed the effect of shape resonances on the differential cross sections for this insertion reaction by performing additional QM calculations. We have found that, in some cases, the resonance gives rise to a large enhancement of extreme backward scattering for specific final states. Our results also show that, in order to yield a significant change in the state-resolved differential cross section, the resonance has to be associated with constructive interference between groups of partial waves, which requires not getting blurred by the participation of many product helicity states.

Automated summary

Shape resonances occur when a system is trapped in an internuclear potential well after tunneling through a barrier, leading to peaks in the collision energy dependence of the cross section. These resonances can enhance extreme backward scattering in specific final states, and require constructive interference between groups of partial waves to yield a significant change in the state-resolved differential cross section.