Role of Low Energy Resonances in the Stereodynamics of Cold He +D2Collisions

In recent experiments using the Stark-induced adiabatic Ramanpassage technique, Zhou et al. (J. Chem. Phys.2021,154, 104309;Science2021,374,960-964) measured the product's angular distribution for the collisions between Heand aligned D2molecules at cold collision energies. The signatures of the angulardistributions were attributed to an= 2 resonance that governs scattering at lowenergies. Afirst-principles quantum mechanical treatment of this problem ispresented here using a highly accurate interaction potential for the He-H2system.Our results predict a very intense= 1 resonance at low energies, leading to angulardistributions that differ from those measured in the experiment. A good agreementwith the experiment is achieved only when the= 1 resonance is artificiallyremoved, for example, by excluding the lowest energies present in the experimentalvelocity distribution. Our analysis revealed that neither the position nor the intensityof the= 1 resonance significantly changes when the interaction potential ismodified within its predicted uncertainties. Energy-resolved measurements may help to resolve the discrepancy

Automated summary

This study discusses an experiment using the Stark-induced adiabatic Raman passage technique, which investigates the angular distribution between He and aligned D2 molecules at cold collision energies. Results show the presence of an n=2 resonance in low energies in the experiment, while a strong n=1 resonance is predicted at low energies in simulations. Agreement with experimental results requires the exclusion of this n=1 resonance.