Experimental and Theoretical Investigation of Resonances in Low-Energy NO-H$_2$ collisions

TL;DR

This study experimentally and theoretically investigates low-energy NO-H$_2$ collision resonances, revealing detailed resonance features and partial wave contributions, and discriminating between different potential energy surfaces.

Contribution

It provides new experimental data in the 0.4-10 cm$^{-1}$ range, compares two potential energy surfaces, and analyzes resonance contributions from partial waves in NO-H$_2$ collisions.

Findings

Resonance features were resolved in cross sections.

Comparison discriminated between two potential energy surfaces.

Partial wave analysis identified resonance contributions.

Abstract

The experimental characterization of scattering resonances in low energy collisions has proven to be a stringent test for quantum chemistry calculations. Previous measurements on the NO-H$_2$ system at energies down to $10$ cm$^{-1}$ challenged the most sophisticated calculations of potential energy surfaces available. In this report, we continue these investigations by measuring the scattering behavior of the NO-H$_2$ system in the previously unexplored $0.4 - 10$ cm$^{-1}$ region for the parity changing de-excitation channel of NO. We study state-specific inelastic collisions with both \textit{para}- and \textit{ortho}-H$_2$ in a crossed molecular beam experiment involving Stark deceleration and velocity map imaging. We are able to resolve resonance features in the measured integral and differential cross sections. Results are compared to predictions from two previously available potential energy surfaces and we are able to clearly discriminate between the two potentials. We furthermore identify the partial wave contributions to these resonances, and investigate the nature of the differences between collisions with \textit{para}- and \textit{ortho}-H$_2$. Additionally, we tune the energy spreads in the experiment to our advantage to probe scattering behavior at energies beyond our mean experimental limit.