Vibrational Assignments of Lithium Alkyl Carbonate and Lithium Alkoxide in the Infrared Spectra An Ab Initio MO Study

We conducted ab initio molecular orbital calculations on stable monomer and dimer structures of lithium alkyl carbonates (methyl, ethyl, and propyl carbonate lithium) and lithium alkoxides (lithium methoxide, lithium ethoxide, lithium propoxide, and lithium butoxide). We confirmed that both lithium alkyl carbonates and lithium alkoxides adopted the dimer structure. The dimerization energies were approximately constant and independent of the alkyl group chain length. The dimerization energy was 214 kJ/mol for lithium alkyl carbonates and 266 kJ/mol for lithium alkoxides. Assignments of the vibration modes for each calculated frequency of lithium alkyl carbonates and lithium alkoxides were carried out. Vibrational frequency analysis recognized a dramatic vibrational frequency shift in the parts of the structure which changed significantly between the monomer and dimer structures (the lithium carbonate structure for lithium alkyl carbonates and the COLi structure for lithium alkoxides). Good agreement was achieved between calculated and experimental vibrational frequencies by shifting the frequency of the dimers. © 2000 The Electrochemical Society. All rights reserved.