Gas Phase Ion Chemistry

Our research is focused on studying the intrinsic chemical and physical properties of reactive intermediates. The intrinsic properties of intermediates can only be explored in the absence of solvation effects, consequently, these studies must be conducted in the gas phase. All of our studies involve the use of gas phase ion techniques, specifically Fourier transform mass spectrometry (FTMS). FTMS is the most powerful gas phase ion technique for probing the chemical and physical properties of ions. FTMS employs crossed magnetic and electric fields that form an electromagnetic bottle for trapping ions. The ion storage capability of FTMS combined with sophisticated ion manipulation techniques as well as the ability to temporally vary the composition of neutrals in the electromagnetic bottle facilitates the investigation of gas phase ion chemistry at an unprecedented level of sophistication. We are using FTMS to attack a broad range of problems of both fundamental and practical interests. We are primarily interested in structure/reactivity relationships, reaction mechanisms, rearrangement, and mechanisms of decomposition.

All of our research involves metals, either transition or main group metals. Our transition metal centered research involves the activation of simple molecules (e.g., CO, N₂, NO, H₂, CH₄, etc.) by discrete transition metal microclusters and their conversion to more important species. For example, we have found that a TaFe+ ion can dissociate CO and, upon reaction with H₂O, generate C₂H₂. This reaction involves the conversion of two CO molecules to C₂H₂, with water the source for hydrogen:

• TaFe+ + 2CO + H₂O -> FaTeO₂⁺ + C₂H₂

We are also studying the mechanism of a variety of transition metal mediated Cycloaddition reactions including [4 + 2] cycloaddition (Diels-Alder cycloaddition), [2 + 2 + 2] cyclotrimerization reactions, as well as a variety of other cycloaddition reactions. We are also studying the activation of unactivated C-H bonds as well as the mechanism of desulfurization of thiophenic compounds by transition metal complexes. Finally, the activation of Si-X bonds by transition metal complexes and the generation, characterization, and properties of M-silene (silene = R₂Si=CR₂) and M-silylene (silylene = :SiR₂) are active areas.

Our research in main group chemistry concerns the mechanism of organometallic chemical vapor deposition (OMCVD). We are studying the mechanisms of decomposition of organosilicon ions that, in many cases, are very complex. In addition, the mechanism of decomposition of a variety of group 13 and 15 species as well as group 14 and 16 species are under investigation. Particularly intriguing in these studies is the prospect for generating and characterizing group 13/15 dimers containing a double bond. For example, RGa=AsR' is proposed as a key intermediate in the preparation of GaAs films, however, these species have not been observed to date. The chemistry of microclusters of these semiconductor materials is also under investigation.

Selected Publications

H. Chen, D. B. Jacobson and B. S.Freiser, “Generation, Characterization, and Reactivity of the Transition Metal-o-Benzyne Analog of Pyrazine (Fe + -2,3-Didehydropyrazine) in the Gas Phase: An Experimental and Theoretical Study,” Organometallics 1999, 18, 1774.

H. Chen, D. B. Jacobson and B. S.Freiser, “Interconversion of FeC 2 H 3 + and HFeC 2 H 2 + : AnFT-ICR and Density Functional Study,” Organometallics 1999, 18, 5460.

K. J. Auberry, Y. G. Byun, D. B. Jacobson and B. S. Freiser, “Kinetics of Metallocarbohedranes: An FT-ICR Mass Spectrometry Study of the Association Reactions of Ti 8 C1 2 + with Polar and Nonpolar Molecules,” J. Phys. Chem. A 1999, 103, 9029.

H. Chen, D. B. Jacobson and B. S.Freiser, “Structure and Reactivity Studies of CoHNO + in the Gas Phase,” J. Phys. Chem. A 1999, 103, 10884.