Abstract
Observation of molecular dynamics with quantum state resolution is one of the major challenges in chemical physics. Complete characterization of collision dynamics leads to the microscopic understanding and unraveling of different quantum phenomena such as scattering resonances. Here we present an experimental approach for observing molecular dynamics involving neutral particles and ions that is capable of providing state-to-state mapping of the dynamics. We use Penning ionization reaction between argon and metastable helium to generate argon ion and ground state helium atom pairs at separation of several angstroms. The energy of an ejected electron carries the information about the initial electronic state of an ion. The coincidence detection of ionic products provides a state resolved description of the post-ionization ion-neutral dynamics. We demonstrate that correlation between the electron and ion energy spectra enables us to directly observe the spin-orbit excited Feshbach resonance state of HeAr+. We measure the lifetime of the quasi-bound HeAr+A2 state and discuss possible applications of our method.
Highlights
Observation of molecular dynamics with quantum state resolution is one of the major challenges in chemical physics
As a first demonstration of our approach, we study the Penning ionization (PI) and associative ionization (AI) channels of the collision between metastable helium and neutral argon
The ionization process is described by the projection of the incoming wave function weighted by the square root of the autoionization width Γ(R) on one of the three possible ion-neutral potential surfaces, which are asymptotically separated on energy scale by the spin–orbit interaction energy of Ar+ (ΔESO = 0.178 eV)
Summary
Observation of molecular dynamics with quantum state resolution is one of the major challenges in chemical physics. We present an experimental approach where ionization induced by collision between excited noble gas and a neutral particle is used to initiate dynamics between ions and noble gas atoms. Without the correlation, electron energy provides information only about the initial state of the PI ion.
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