Title: Deciphering the mechanisms of surface photoinduced and photocatalytic reactions using femtosecond UV and XUV laser pulses

Abstract: 

The detection of highly unstable intermediate species during surface photoinduced and photocatalytic reactions and the correlation of their dynamics with the surface properties is crucial to fully understand and control heterogeneous reactions. In this work, an experimental methodology that combines surface mass spectrometry with a femtosecond pump-probe technique and ultraviolet multiphoton or extreme ultraviolet single photon ionization is employed to decipher the mechanisms of surface photoinduced and photocatalytic reactions. The technique relies on the detection of highly unstable intermediate species and final products with time-, mass-, and energy resolution.

In the first part of the talk, the photoinduced reaction dynamics of methyl iodide adsorbed on an amorphous cerium oxide ultrathin film is investigated to understand the effect of random molecular adsorption geometries on the surface reaction. In the second part of the talk, an experiment is presented in which the ultrafast photodissociation dynamics of CH3Br molecules adsorbed on variable size Au clusters on MgO/Mo(100) is investigated by monitoring the CH3+ transient evolution. Extreme-ultraviolet photoemission spectroscopy in combination with theoretical calculations are employed to study the electronic structure of the Au cluster on MgO/Mo(100). Changes in the ultrafast dynamics of CH3+ fragment are correlated with the electronic structure of Au as it evolves from monomers to small nonmetallic clusters to larger nanoparticles with a metallic character.

In the last part to the talk, an experiment will be presented in which the photoinduced reaction of D2O in the presence of CH3I is monitored on an n-type (Nb) doped TiO2(100) surface. In this experiment intermediate species such as D, OD, and DO2 are detected when only water is dosed on the TiO2 (100) surface. When both D2O and CH3I are dosed on the surface, besides the intermediate species mention above, CH3 and I radicals as well as methane (CH3D) and methanol (CH3OD) are observed. Details about the surface properties and how this affects the surface chemical reactions will be provided.

About the Speaker: Dr. Mihai E. Vaida is an associate professor in the Department of Physics and a member of the Renewable Energy and Chemical Transformation Cluster at the University of Central Florida (UCF). His research, which combines surface science and ultrafast spectroscopy, focuses on understanding the properties of catalytic and photocatalytic materials as well as surface reaction mechanisms. Prior to joining UCF, he earned a doctoral degree in physical chemistry from the University of Ulm, Germany and was a Postdoctoral Research Fellow at the University of California, Berkeley. He received several awards including NSF Career award, UCF Research Incentive Award, UCF COS Excellence in Research Award, DAAD Scholarship (German Academic Exchange Program), Erasmus and Erasmus Plus Scholarships, and EMSPS (European Mobility Scheme for Physics Students) Scholarship.