Speaker
Description
Achieving a molecular-level understanding of complex chemical reactions requires a detailed mapping of their elementary dynamics. Among these, charge transfer during two-body molecular dissociation has been investigated in pioneering experiments as a function of the distance between the two separating fragments (see e.g., Erk et al. 2014 and Schnorr et al. 2014). Here we build upon a study by Köckert et al. (2022), investigating how fragment orientation influences charge transfer during photo-dissociation. We employ an ultra-short pump pulse to trigger two-body dissociation in bromoiodomethane and chloroiodomethane. Because the halomethyl fragment’s center of mass is off-axis relative to the cleaved C–I bond, dissociation induces a rapid rotation of the neutral fragment. Subsequent to triggering the photo-dissociation, at well-controlled, varied time delays, we site-selectively ionize the iodine atom using an intense X-ray pulse. The occurrence of charge transfer following this ionization, as deduced from the detected ionic products and their kinetic energies, allows us to map the probability for charge transfer depending on charge state configuration and fragment orientation. Signals are isolated by mass, charge, kinetic energy, and delay using a velocity map imaging spectrometer combined with a Timepix3 nanosecond-timestamping camera. In this work, we present the successful extraction of these rotational signatures from our multi-coincidence data. We map the charge transfer probability across a wide range of charge states as a function of both distance and orientation, providing direct evidence of the system crossing the classical over-the-barrier critical distance, at which charge transfer is inhibited, multiple times due to fragment rotation.
| Scientific Topics | AMO Physics |
|---|