University of Arizona Chemistry DepartmentSmith Research Group

Free Jets
Ion Traps
Laval Nozzles
Titan Project


One area of our research program is centered about the study of molecular collision dynamics in the gas phase. A large part of the work, both experimental and theoretical, is associated with the development of new supersonic flow reactors for low temperature kinetic measurement. These techniques now allow the study of gas phase ion and free radical reactions from 300 K down to temperatures below 1 K. The results are providing critical insight into reaction mechanisms and find direct application to the study of chemical evolution in interstellar media and terrestrial and planetary atmospheres. Experimental studies have focused on the behavior of termolecular association processes and their relation to the lifetimes of bimolecular encounters, the dynamics of bimolecular light and heavy atom transfer reactions and electronic, vibrational and rotational energy transfer processes of small molecules and ions at low temperature.

In this area we are currently studying 10K reactions of quantum state selected HBr+(V,J,I) with HBr and H2 to gain insight into competition between relocation, energy transfer and chemical reaction of internally excited species. We are also looking at the low temperature rates of reaction (50-250K) of NH radical and H and D atoms with variety of small molecules related to gas chemistry of planetary atmospheres and the ISM.

Aligned with our continuing interests in laser assisted chemistry we are studying reactions with demonstrated sensitivity to vibrational excitation. We have used this phenomenon to perform sensitive near single ion absorption spectroscopy in the infrared and are working to expand this to cover small molecular cations and anions for which vibrational spectroscopy is poorly understood. In this regard we are currently planning to build a 10K ion trap in our Tucson laboratory to continue this work. This radiofrequency ring electrode trap will allow the ability to study both ion spectroscopy as well as slow collisional processes, such as radiation association, not easily amenable to supersonic flow systems. The trap will be specifically designed to investigate ion reactions with unstable species such as atoms and small radicals.

A new direction for our group has involved the study of the organic chemistry of Saturn's large moon, Titan. Ion and photochemistry in the dense upper atomosphere of this object produces large quantities of organic aerosols, dubbed tholins. These tholins fall to the 100K surface and providing the organic feedstock for subsequent hydrolysis or oxidation chemistry. The development of this chemistry , its potential role in prebiological processes on Titan are of particular interest. The work in our group involves laboratory generation of tholin analogues and the determination of physical characteristics and chemical reactivity of this complex material. Short term goals are associated with providing interpretive insight into the Cassini-Huygens mission data coming back in early 2005 as well as to provide design input for a new Titan surface probe containing the instrumentation for a potential follow-on mission to probe directly the Titan surface chemistry. This work is in collaboration with scientists at the UA Planetary Science Department, Caltech and the Jet Propulsion Laboratory. 

Prof. Mark A. Smith
Department Head
Department of Chemistry
University of Arizona
P.O. Box 210041
Tucson, Arizona  85721
Phone:  520.621.2115 FAX:  520.621.8407