Tomography of Feshbach resonance states.

Abstract 

Feshbach resonances are fundamental to interparticle interactions and 
become particularly important in cold collisions with atoms, ions, and 
molecules. In this work, we present the detection of Feshbach resonances in 
a benchmark system for strongly interacting and highly anisotropic collisions: 
molecular hydrogen ions colliding with noble gas atoms. The collisions are 
launched by cold Penning ionization, which exclusively populates Feshbach 
resonances that span both short- and long-range parts of the interaction 
potential. We resolved all final molecular channels in a tomographic manner 
using ion-electron coincidence detection. We demonstrate the nonstatistical 
nature of the final-state distribution. By performing quantum scattering 
calculations on ab initio potential energy surfaces, we show that the isolation 
of the Feshbach resonance pathways reveals their distinctive fingerprints in 
the collision outcome. Quantum scattering resonances, and Feshbach 
resonances in particular, are the key features of cold collisions that can 
fundamentally change collision outcomes. Numerous previous experiments 
have mainly focused on the initial channel, providing limited insight into the 
resonant scattering dynamics. Margulis et al. developed a method in which 
the energetics and decay channels of Feshbach resonances, formed by 
collisions induced by Penning ionization of metastable helium or neon atoms 
and the ground-state hydrogen molecule, were mapped out by ion-electron 
coincidence velocity map imaging with a precision of several Kelvin, enough 
to resolve all the final rovibrational quantum states in a single measurement. 
The proposed method offers a new approach to quantum state mapping of 
resonant collision dynamics. Feshbach resonances in reaction complexes of 
H?? ions and rare gas atoms are resolved in a tomographic manner.