Department of Chemistry, University of Central Florida

Research overview/recruitment seminar

Prof. Denisia M. Popolan-Vaida

Ozone an Important Player in Atmospheric and Combustion Chemistry

Ozonolysis reactions have been intensively investigated due to their importance in many branches of chemistry such as synthetic organic, atmospheric, and combustion chemistry, but the mechanistic details are not fully understood in part due to limitations in detecting intermediate species. In the reactivity of complex chemical systems, the crucial reaction steps are often determined by highly unstable intermediate species. Often, the intermediates are formed relatively slowly and may react away rapidly, so they are often difficult to isolate and study in detail. The nature of the intermediates can determine the impact of the reaction; for example, in ignition chemistry, the formation of reactive radicals may accelerate ignition while the formation of closed shell species tends to inhibit ignition.

In the first part of the talk, I will show how mass spectrometric methods and synchrotron‑based techniques are used to selectively study individual processes involved in the ozone assisted oxidation reaction of alkenes. An atmospheric pressure jet stirred reactor in conjunction with a high-resolution tunable synchrotron photoionization time-of-flight mass spectrometer is used to monitor the chemical transformations of key intermediates of the reaction of trans-2-butene with ozone via identification and quantification of previously elusive intermediate species. A variety of multi-functional peroxide species are identified based on the experimentally measured photoionization spectra and theoretically determined ionization energies. A reaction network of the Criegee intermediates (CIs) is identified, which is described by the addition of CIs to trans-2-butene, water, and other molecules containing hydroxy, aldehyde, and hydroperoxyl functional groups. In addition, the detection of additional oxygenated species such as methanol, ketene, aldehyde, and acetoin suggest multiple active oxidation routes. These findings improve our understanding of the reaction of alkenes with ozone, providing insights relevant to the formation mechanism of tropospheric aerosol building blocks.

In the second part of the talk, I will show how high-resolution mass spectrometry in conjunction with standard aerosol techniques are used to study the fundamental heterogeneous reaction between short unsaturated dicarboxylic acids aerosol particles and ozone. Low molecular weight dicarboxylic acids, either directly emitted or formed in chemical processes, are found to be a significant component of tropospheric aerosols. Maleic acid was selected as surrogate to assess the potential chemical transformation of short unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry. The experimentally determined reactive uptake coefficient is found to increase with decreasing particle diameter. In addition, cloud condensation nuclei (CCN) activity investigations revealed an increase of the hygroscopicity of maleic acid particle after the reaction with ozone. The rate of change in CCN activity is important to access the role of these particles in cloud formation.

Prof. Matthieu Baudelet

Quantitative forensic analysis: our approach for calibration strategies and trace analysis

Forensic analysis keeps evolving because of the increasing ability of our research community to provide information with new approaches and new technology. Nonetheless, in order to provide a reliable information to the judicial system, we need to be able to provide quantitative data. In this talk we will discuss the different aspects of the research performed in my group:

• The elemental analysis of tire evidence shining a new light to road crime forensics with the help of engineers, statisticians and Florida Law Enforcement
• The quantitative analysis of hard biomaterials by laser-ablation techniques providing new tools to Forensic Anthropology and Internal Medicine.
• The multidisciplinary approach to pollen analysis bringing together researchers from chemistry, plant biology, biomedicine and local horticultural gardens