Conformational Analysis of the Molecular Complexes of Sodium with Methanol and 1,2-Ethanediol: Photoionization and ab Initio Molecular Orbital Studies

Abstract

The molecular complexes of the sodium atoms with methanol and 1,2-ethanediol were generated in a flow reactor and studied with photoionization mass spectrometry. The photoionization efficiency spectra of these complexes were measured and the ionization threshold energies were determined by the method of the Watanabe plots. The conformation-dependent bond dissociation energies and ionization energies of these complexes were also calculated by ab initio molecular orbital methods. The photoionization threshold energies of the sodium/methanol complex was determined to be 4.30 ( 0.02 eV, a value in good agreement with the ab initio prediction. Guided by the theoretical results, the experimental photoionization threshold energy of the cyclic conformers of the sodium/1,2-ethanediol complex was determined to be 3.95 ( 0.02 eV and that of the conformers with the concerted intramolecular H-bond was determined to be 4.32 ( 0.01 eV. The bond dissociation energy of the sodium/methanol complex was determined to be 0.28 eV. The interplay of the sodium complexation bonding and the intramolecular hydrogen bonding and its effects on both the bonding energies and the ionization energies of the conformers were discussed. The conformation-dependent physical properties of the corresponding cationic states of these complexes were also reported. Comparisons of the physical and chemical properties among the sodium/1,2-ethanediol, sodium/1,2-dimethoxyethane, and potassium/1,2-ethanediol complexes were emphasized in this study.