Oxygen 1s Photoelectron Spectroscopy of Gaseous Alcohols and the σ-Inductive Properties of Alkyl Groups

Abstract

This study presents a comprehensive investigation of alcohol molecules in the gas phase using oxygen 1s X-ray photoelectron spectroscopy (O1s XPS), complemented by carbon 1s XPS. We report ionization energies for a diverse set of aliphatic, alicyclic, aromatic, and unsaturated alcohols with an accuracy of 0.02 eV (O1s) and 0.035 eV (C1s). The resulting dataset provides a benchmark for electronic structure theory, a reference for spectroscopic analyses, and high-quality input for machine-learning models. By decomposing the ionization energies into initial- and final-state contributions, O1s chemical shifts are used to explore the electronic role of hydrocarbon substituents in alcohols. Among aliphatic and alicyclic alkyls, the capacity to donate electrons through σ-bond polarization in the neutral molecule was found to increase systematically through the sequence from methyl, via branched and linear primary alkyls, to secondary alkyls, and tert-butyl.