Physics - chemistry seminar

Speaker:

Robert E. Continetti

University of California

Title:

Dissociation Dynamics and Particle Impacts: Electrostatic Ion Beam Traps and Charge Detection Mass Spectrometry

Abstract:

Experimental chemical physics in the field of reaction dynamics seeks to observe and understand the outcome of molecular collisions and dissociation processes, in the gas phase ranging from atomic and diatomic systems all the way to studies of aerosols and other nanoparticles. Two extreme examples of experimental studies of reaction dynamics will be presented, making use of similar ion beam techniques including electrostatic ion beam traps and time- and position-sensitive detectors.

In the first instance, a benchmark measurement of the dynamics of an elementary chemical reaction will be reviewed, wherein the negatively charge F¯(H₂O) complex is used to promote and study the F + H₂O ? OH + HF neutral reaction following photodetachment. This type of experiment can be carried out by the technique of photoelectron-photofragment coincidence spectroscopy. This four-atom system has six internal degrees of freedom and represents a grand-challenge for accurate calculations of the Born-Oppenheimer potential energy surfaces and quantum dynamics of the system. Comparison of experiment with theoretical predictions shows that this system can be treated with near chemical accuracy, but there are still challenges in accounting for excited states and long-lived complexes.¹

In the second instance, a new single-particle dust accelerator/decelerator will be discussed.² This apparatus makes use of similar experimental techniques, but is applied to much more complex systems: micron and sub-micron-sized nanoparticles. The mass and charge of single nanoparticles can be measured using charge detection mass spectrometry and the particle then accelerated or decelerated to the desired final velocity for studies of particle impact with surfaces. Applications to measurements of the coefficient of restitution for polystyrene latex spheres and tin nanoparticles and the durability of free-standing nanostructures with respect to particle impact will be presented.

References

[1] R. Otto, J. Ma, A.W. Ray, J.S. Daluz, J. Li, H. Guo and R.E. Continetti, Science 343, 396 (2014)

[2] B.D. Adamson, M.E.C. Miller and R.E. Continetti, EPJ Tech. and Instrum. 4:2 (2017)

 Coffee and cake will be served at 14:00