Equipment for Probing Ultracold Reaction Intermediates
Abstract
Recent findings from ultracold chemistry experiments have exposed new and interesting phenomena in chemistry, from molecular bonds 100’s of Å long to reaction intermediates that live for 100’s of micros, there is much exotic chemistry to be explored in this regime. Notably, the existence of long-lived reaction intermediates shows promise for the probing of the structures of these complexes directly produced from bimolecular reactions, allowing for the tracking of reaction mechanisms directly. In particular, such experiments show promise for the observation of a TS directly produced from a bimolecular collision, a long sought goal in chemistry. Such experiments are within reach, as current ultracold chemistry experiments are readily capable of producing 104 molecules with temperatures less than 1 microK, though our instrument is uniquely capable of probing the presence of reaction intermediates directly through the use of ion imaging. Unfortunately, while this technique can determine the presence and lifetime of species formed in bimolecular reactions, it is blind to the structures of the species produced. This can be remedied by modifying our detector architecture such that we can perform high-resolution spectroscopy. Here, we propose to modify our ultracold chemistry instrument to allow for the performance of high-resolution photoelectron imaging, allowing for the structural characterization of many of the species produced from collisions with KRb, our platform for ultracold chemistry. Such modifications entail shielding the detector from stray fields that may distort the photoelectron images and increasing the number of molecules produced by our instrument to make data collection comparable to conventional photoelectron experiments through upgrading existing hardware. Further, introduction of a new laser system for the production of vibrationally excited molecules will pro- vide another handle to control the reactions that take place in this fully-quantum regime. Upon development of the instrument, we intend to first study the endothermic KRb + Rb reaction, for which the KRb2 intermediate has been found to live for approximately 300 micros. This lifetime is 105 longer than predicted by statistical theories and remains an open question in the theoretical community. Determination of the structure of this species may elucidate the mechanism of this reaction and provide an answer for its anomalously long lifetime. Further, reactions of vibrationally excited KRb (ν = 1) with Rb are exothermic and will allow for the probing of this reaction as it crosses from endo- to exothermic. Finally, we will probe the KRb + KRb reaction for which two intermediates are expected, separated by a TS corresponding to a submerged barrier on the reaction path. Our previous work on this system has mapped the reaction with state-to-state resolution, finding that nuclear spins are conserved throughout the reaction and that the intermediates ergodically sample the reaction phase space. We thus expect to observe signal from both reaction intermediates in our photoelectron images, which may be used to track the relative populations of these species as a function of reaction time, reactant conditions, and external fields. Such information would elucidate the fundamental mechanisms by which energy is transferred between reactants and products in a chemical reaction.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 29, 2024
- Source ID
- FA95502310122
Entities
People
- Kang-Kuen Ni
Organizations
- Air Force Office of Scientific Research
- President and Fellows of Harvard College
- United States Air Force