High-resolution imaging of velocity-controlled molecular collisions using counterpropagating beams

TL;DR

This paper demonstrates ultrahigh-resolution measurements of molecular collision cross sections using counterpropagating beams, combining Stark deceleration and velocity map imaging to achieve unprecedented angular resolution and symmetry.

Contribution

It introduces a counterpropagating beam geometry that minimizes velocity spread effects and enhances image symmetry, enabling highly precise differential cross section measurements.

Findings

Achieved angular resolution of approximately 0.3 degrees.

Observed state-resolved diffraction oscillations in cross sections.

Provided experimental data to evaluate  initio potential energy surfaces.

Abstract

We present ultrahigh-resolution measurements of state-to-state inelastic differential cross sections for NO-Ne and NO-Ar collisions, obtained by combining the Stark deceleration and velocity map imaging techniques. We show that for counterpropagating crossed beam geometries, the effect of the velocity spreads of the reagent beams on the angular resolution of the images is minimized. Futhermore, the counterpropagating geometry results in images that are symmetric with respect to the relative velocity vector. This allows for the use of inverse Abel transformation methods that enhance the resolution further. State-resolved diffraction oscillations in the differential cross sections are measured with an angular resolution approaching 0.3$^\circ$. Distinct structures observed in the cross sections gauge the quality of recent \emph{ab initio} potential energy surfaces for NO-rare gas atom collisions with unprecedented precision.