Timothy Steimle

The generation, detection and characterization of transition metal containing molecules associated with the modeling catalysis are the focus of our current research. Efficacious synthesis of new catalysts will only be accomplished when there is a clear understanding of the associated microscopic molecular steps and achieving this scientific understanding has been a long-standing scientific objective. Theoretical insight, coupled with fundamental experimentation, can be most influential in modeling supported metal cluster and supported molecular catalyst used to process gaseous reagents and effluents (e.g. automobile emission) because of their very molecular nature. It is realistic that the reactions of a single metal atom, or possibly a metal dimer, with simple gaseous reagents are reasonable first order model systems for emulating metal cluster and molecular supported catalysis. These simple and highly quantifiable systems are the focus of the current and proposed research.

The information we seek is both the geometric and electronic structure for metal carbides, carbenes, imides, nitrides, thiols, cyanides, halides, hydroxides, and hydrides from the reaction of CH4, NH3, H2S, and CH 3CN, CH3Cl, CH3OH and H2. All experiments to date have depended upon recording and analyzing ultra-high resolution electronic spectra. We have been implementing the laser ablation/supersonic expansion scheme for sample production, which allows us to control the complexity of the spectra by controlling the rotational temperature to as low as 10 K. The electronic temperature of the sample is much higher facilitating studies of low-lying excited states, which are populated in the reaction. Unlike almost all other groups that use these sources, we skim the supersonic expansion to form a well-collimated molecular beam. The skimming and our use of single frequency lasers results in spectral resolution of < 40 MHz linewidth, which is unprecedented for this class of transient molecules and is required for full exploitation of the information content of electronic spectra. Particular emphasis has been, and will continue to be, placed on the determination of ground and excited state permanent electric dipole moments, m, which are the most fundamental electrostatic property of a molecule and enter into the description of numerous phenomena. A comparison of experimentally derived and theoretically predicted values of m is the most useful gauge of the quality of electronic wave function generated by modern computational methods.

The experiments include:

High-resolution laser induced fluorescence spectroscopy

Pump/probe microwave optical double resonance

Transient frequency modulation spectroscopy

and Time-of-flight mass spectrometry