Current Research

Our research focuses on the mechanisms of gas phase ion-molecule reactions.  It has applications to planetary atmospheres, interstellar chemistry, chemical vapor deposition, and combustion.  Our planetary atmosphere studies have concentrated on Titan, a planetary satellite of Saturn.  The Saturnian system is presently being visited by the highly successful Cassini spacecraft which, in the last seven years, has made many passes through the Titan atmosphere.  A quadrupole mass spectrometer (1 to 99 amu) on Cassini has been able to obtained mass spectra on each pass.  However, these do not directly give any information about molecular composition.  For this, it requires a chemical model of the atmosphere so that predicted mass spectra can be compared with observed mass spectra.  Agreement between these then gives information on molecular composition provided that the chemical scheme contains all the many important reactions and their kinetic data (rate constants and products) are available.  We study these reactions in the laboratory to provide these data.  Very recently and surprisingly, another experiment on Cassini has shown the presence of positive ions up to 350 amu and negative ions up to 8000 amu. The latter indicates the presence of Polycyclic Aromatic Hydrocarbons, PAH’s and PANH’s, aerosols and tholins.  Thus, many of the reactions involve hydrocarbon rings. Without such kinetic data, the molecular composition of the atmosphere would remain unknown.  This would be a great loss since Titan is believed to have an atmosphere much like a Pre-Biotic Earth.

The chemistry of the interstellar medium has much in common with the Titan atmosphere although with different physical conditions.  Many of the ~150 molecules there have been detected by microwave emissions and thus, unlike Titan, their molecular compositions are well known.  Many organic molecules are present, both ions and neutrals.  Our contribution is to study reactions which result in the observed species and to predict other species for which to search.  These interstellar molecules are present in regions where stars and planetary systems are being formed and thus bathe the planets with Pre-Life molecules.

The laboratory measurements are made using a Flowing Afterglow and a Selected Ion Flow Tube, shown below.

Reaction processes that can be studied including proton transfer, charge transfer, hydrogen abstraction, association, recombination and many more and as a function of temperature (80 to 600 K).

Selected Publications