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                                      Physics

 

 

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Seminars

Seminars will be held in room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise. When necessary, virtual seminar Zoom login instructions will be sent out via email.


Spring 2023




January 19, 2022, 4:00 PM

Prof. Itzik Ben-Itzhak,
J.R. Macdonald Laboratory, Physics Department, Kansas State University
Coincidence momentum imaging of photo-induced multi-body fragmentation:
a path toward understanding molecular dynamics with increasing complexity

(Host: Tom Weinacht)

Experimental studies of the multi-body fragmentation of polyatomic molecules using coincidence momentum imaging techniques have become more attainable with advancements in detector and light source technologies. The goal of our research group is to apply these techniques to gain detailed insight into both concerted and sequential (also known as simultaneous and stepwise, respectively) molecular dynamics, and when possible, follow their time evolution.


One common approach for relating the momentum images to the stationary or time-dependent molecular structure relies on the implementation of Coulomb explosion imaging (CEI), which inherently assumes a rapid concerted fragmentation. This assumption was originally fulfilled by stripping fast molecular ion beams in ultra-thin foils [1]. However, in photo-induced molecular processes the validity of this assumption is in question. Clearly sequential fragmentation is a process that can prevent the proper application of CEI, and therefore we need to separate concerted and sequential fragmentation–a goal that we accomplish by using native frames analysis [2].


The main advantage of the native-frames method is in providing an analysis and interpretation framework for multi-body fragmentation, which is typically challenging due to the high dimensionality inherent in such data. In one example, we study the sequential fragmentation of D2O molecules into D++D++O+2e- following double ionization by a single photon [3]. Namely, we pinpoint the precise electronic states involved in each sequential breakup step and image the internal energy of the OD+ intermediate above the D++O(3P) dissociation limit. In addition, we show how the angular momentum of the intermediate molecule manifests as a threshold behavior in the kinetic energy release of the second breakup step. We will also discuss experimental progress toward imaging four-body sequential fragmentation and toward time-resolved studies.


This work is in collaboration with the groups of Daniel Rolles, Artem Rudenko, Thorsten Weber, Bill McCurdy, Robert Lucchese, Tom Rescigno, Daniel Slaughter, Joshua Williams, Allen Landers, and Reinhard Dörner.


References:
[1] Z. Vager, R. Naaman, and E.P. Kanter, Science 244, 426 (1989)
[2] J. Rajput, T. Severt, et al., Phys. Rev. Lett. 120, 103001 (2018)
[3] T. Severt et al., Nature Communications 13, 5146 (2022)


*Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy under Award No. DE-FG02-86ER13491



February 20, 2022, 4:00 PM

Dr. Marjan Mirahmadi,
Fritz Haber Institute of the Max Planck Society
TBD

(Host: Jesús Pérez Ríos)

TBD

2023