Author ORCID Identifier

https://orcid.org/0000-0002-8276-2847

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Chemistry

First Advisor

Dr. Dong-Sheng Yang

Abstract

The C-C and C-H bonds have high bond strength and low polarization, which make many small hydrocarbons too inert to react with other molecules under ambient pressure and temperature conditions. Therefore, activation of these bonds is required to convert such small molecules into other value-added chemicals. Among various bond activation methods, metal activation is widely used and reported in the literature, because of its relatively mild reaction conditions and high selectivity.

In this work, Ce atom reactions with several small hydrocarbons are carried out in a pulsed laser vaporization supersonic molecular beam source, and Ce -hydrocarbon species are observed with time-of-flight mass spectrometry and characterized by mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. The small hydrocarbon compounds include ethylene, propene, 2-butene, and iso-butene. In addition to these alkene molecules, ammonia is used to investigate the N-H bond activation and compare with the C-H activation of the alkene molecules. Ammonia reaction with La atom is also included in this work to help investigate effects of the Ce 4f1 electron on the Ce reactivity and MATI spectra of Ce-containing species. The theoretical calculations include quantum chemical computations and spectral simulations. The quantum chemical methods include density functional theory, electron correlation, and spin-orbit coupling, and the spectral simulations are based on multi-dimensional Frack-Condon factor calculations.

Vibrationally-resolved MATI spectra are obtained for Ce(C2H2) formed through ethylene dehydrogenation, Ce(C3Hn) (n = 4 and 6) by the C-H and C-C bond activation of propene, Ce(C4H6) two isomers from the C-C bond coupling of ethylene and dehydrogenation of 2- and iso-butene, and LnNH (Ln= La and Ce) formed in the Ce and La reactions with ammonia. The MATI spectra of Ce-hydrocarbon and CeNH complexes consist of two or more vibronic band systems due to spin-orbit coupling between the Ce 4f and 6s electrons, while the spectrum of LaNH has only one vibronic band system. The ground valence electron configurations of all Ce-containing species are Ce 4f16s1, while that of LaNH is La 6s1. Ionization removes the Ce 6s1 or La 6s1 electron and produces doublet electronic states for the Ce-containing species and a singlet state for LaNH. The remaining two 5d electrons that are associated with bare Ce or La atom are spin paired in one or two molecular orbitals that are in binding combinations with ligand orbitals.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.322

Funding Information

National Science Foundation (1362102) 08/01/2014---7/31/2019

National Science Foundation (1800316) 08/15/2018---7/31/2021(Estimated)

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