Near Edge X-ray Absorption Fine Structure Spectra of Linear n- Alkanes: Variation with Chain Length

Abstract

The effect of chain length on the carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of linear n-alkanes has been examined with Transition Potential Density Functional Theory (TP-DFT) calculations. Species from propane (C3H8) to n-icosane (n-C20H42) and selected longer chains were examined. This study focuses on the prominent ‘C-H band’ (287 - 288 eV) in these NEXAFS spectra. TP-DFT calculations show that contributions from interior methylene groups (3 or more positions from the chain end) are similar, while contributions from the terminal methyl and the first methylene groups differ. The evolution of the angle dependent and Rydberg-valence mixing with chain length are also examined.