Molecular free radicals are important chemical inteermediates in various environments, including combustion media and the atmosphere. We are interested in the dynamics of molecular collision processes, including rotational and vibrational energy transfer, photodissociation, and chemical reactions, involving diatomic and small polyatomci free radicals. Our principal tool to study these processes at a quantum-state-resolved level is laser-induced fluoroscence (LIF).
Our group has turned recently to the study of the spectroscopy and kinetics of polyatomic free radicals, which are important in the early stages of the decomposition of energetic materials. We have implemented the technique of cavity ring-down spectroscopy (CRDS) in this work. LIF and resonant-enhanced multiphoton ionization (REMPI) are not applicable to most polyatomic molecules since they generally dissociate upon electronic excitation. CRDS is seeing wide application and is a sensitive absorption-based laser detection method which offers effective absorption path lengths of a kilometer or more in a table-top apparatus. We are employing both UV and IR CRDS on electronic and vibrational transitions.
There is a continuing need for the development of laser diagnostics for the detection of transient species in reactive environments, as well as the detection of explosives and explosive-related compounds in trace quantities. As part of a DoD multi-university research initiative (MURI) headed by Prof. James Spicer of the JHU Department of Material Science and Engineering, our group has explored the use of UV CRDS for the detection of TNT and related compounds in the vapor phase. This technique has been found to display very good sensitivity, but poor selectivity. In recent work, we have partnered in another MURI headed by Prof. Martin Richardson of the U. of Central Florida, in which femtosecond laser-matter interacxtions are being explored. Our principal role in this project is to develop an understanding of the chemical and physical processes which lead to the obserevd optical emissions from the laser-induced plasmas. This has practical applications in the analytical technique of laser-induced breakdwon spectroscopy (LIBS), in which optical emission is used for materials identification, most notably in the detection of explosives.
For the past 30 years our research group has had exceptionally strong links with the theoretical research group of Millard H. Alexander at The University of Maryland.
In service to the chemical physics/physical chemistry community, Professor Dagdigian has been Chair of the Division of Chemical Physics, of the American Chemical Society (APS), and is a Fellow of the APS.