KSEF RDE: Spectroscopic Characterization of Metal-Mediated Hydrocarbon Activation

This work aims to fill a critical experimental gap between the reactivity and mechanisms of metal-mediated hydrocarbon activation reactions. The gap is the lack of the knowledge about the structures and electronic states of reaction intermediates and products. Emphasis is placed on the gas-phase reactions between neutral rare earth atoms (Y, La, Ce, and Pr) and small alkanes, alkenes, and alkynes. Experimental techniques include laser-assisted molecular beam synthesis, time-of-flight mass spectrometry, and pulsed-field ionization-zero electron kinetic energy photoelectron and mass-analyzed threshold ionization spectroscopy. Key experimental results are the precise ionization energies, metal-ligand and ligand-based vibrational frequencies, and electric charge effect on molecular structures. The ionization energy is a basic thermochemical property of a molecule and is used to obtain the metal-ligand bond energy of the neutral molecule through a thermodynamic relation. The metal-ligand vibrational frequencies give direct evidence about the metal-ligand bonding, whereas the ligand-based vibrational frequencies probe the geometry of the metal-activated hydrocarbon. Structural isomers and electronic states of the reaction intermediates and products are identified by comparing the spectroscopic data and theoretical predictions. The success of this work will advance the fundamental understanding about how metal centers activate hydrocarbon transformations.