In this project funded by the Experimental Physical Chemistry Program, Professor Cheuk-Yiu Ng of the University of California, Davis, and his research group will measure the ionization energies, bond dissociation energies, and vibrational and rotational constants of diatomic molecules MX and their cations MX+, where M is a 3d transition metal (M = Sc, Ti, V, Cr, Fe, Co, Ni or Cu) and X is a main group non-metal (X = H, C, N, or O). The general experimental strategy takes advantage of the fact that most MX species possess long-lived, low-lying electronic states that allow a variety of double resonance techniques (initial visible excitation followed by photoionization, photoelectron, or photodissociation) to be applied which can circumvent the normal problems of spectral congestion or signals due to impurity species. Photodissociation studies will involve a two-color velocity-mapped ion-imaging method, which should make it possible to determine accurately not only MX dissociation energies, but the branching ratios of the various dissociation channels. Beyond the specific questions related to diatomic molecules containing transition metals, the techniques developed during this research project will have important impacts in other areas of physical chemistry, astrochemistry, and virtually any other chemical science arena where precise spectral and dissociation energy information is needed. This research project will also provide an excellent vehicle for the training of students and post-doctoral researchers who themselves may go on to develop novel laser based techniques. Finally, Prof. Ng is a participant in the undergraduate research program (MORE/CAMP/MURPPS) for underrepresented minority students at UC Davis.
The main goal of this research program is to obtain precise energetic and spectroscopic data for transition metal-ligated specie and their cations, which are recognized as important industrial catalyses. The high-resolution photoionization studies of transition metal elements and compounds are also relevant to astrophysics for verifying their existence in solar planets and interstellar environments. In this NSF supported project, we have successfully obtained the high-resolution photoionization and photoelectron spectra and have determined highly accurate values for the iron group elements (Fe and Ni), iron carbides (FeC) and nickel carbide (NiC). In order to prepare these species in the gas phase, we have constructed a laser ablation metal beam source. The highly precise ionization energies and bond dissociation energies for these molecules and spectroscopic constants for their cations are important parameters for understanding their physical and chemical bonding properties. These energetic values have been used directly to benchmark state-of-the-art ab initio quantum theoretical calculations. This project involves the development and applications of sophisticated laser sources as well as the design of unique high technology equipment items for frontier scientific research, and thus can serve as an important training ground for undergraduate and graduate students and postdoctoral associates to become the next generation of scientific researchers and engineers.
