Imaging scattering resonances in low-energy inelastic ND$_3$-H$_2$ collisions

TL;DR

This study combines experimental measurements and advanced theoretical calculations to observe and analyze scattering resonances in low-energy inelastic collisions of the polyatomic molecules ND₃ and H₂, advancing understanding of quantum effects in complex molecular systems.

Contribution

It is the first to experimentally resolve scattering resonances in polyatomic symmetric top molecules at low energies and to match these observations with high-level theoretical predictions.

Findings

Strong resonances observed in integral cross sections.

High-resolution differential cross sections measured using VUV laser ionization.

Theoretical predictions required CCSD(T) and CCSDT(Q) level calculations for accurate reproduction.

Abstract

A scattering resonance is one of the most striking quantum effects in low-temperature molecular collisions. Predicted decades ago theoretically, they have only been resolved experimentally for systems involving at most four atoms. Extension to more complex systems is essential to probe the true quantum nature of chemically more relevant processes, but is thus far hampered by major obstacles. Here, we present a joint experimental and theoretical study of scattering resonances in state-to-state inelastic collisions for the six-atom ND$_3$-H$_2$/HD systems across the collision energy range 0.5-25 cm$^{-1}$, bringing this type of experiment into the realm of polyatomic symmetric top molecules. Strong resonances are resolved in the integral cross sections, whereas differential cross sections are measured with high resolution using a laser ionization scheme involving VUV light. The experimental data could only be reproduced using theoretical predictions based on a potential energy surface at the CCSD(T) level of theory with corrections at the CCSDT(Q) level.