Determination of C 1s Core Level Chemical Shifts in Some Langmuir−Blodgett Films Using a Modified Sanderson Formalism

Abstract

The modified Sanderson (MS) formalism for calculation of partial charge on atoms has been shown to yield extremely good correlation between the atomic partial charge in organic molecules and core level binding energies determined using X-ray photoelectron spectroscopy (XPS). The MS approach is used to determine partial charges on the carbons in Langmuir-Blodgett (LB) films of lead arachidate and chloroplatinic acid−octadecylamine complexes and from the atomic charges, expected C 1s chemical shifts. Fits to the C 1s core level spectra from the different LB films agree within experimental error with those predicted by the MS calculation. Identification of additional C 1s spectral components that arise from carbons directly coordinated to the carboxylate carbon/amine group highlights the importance of induction effects on partial atomic charges in molecules, an aspect hitherto not taken into account in XPS studies of LB films. Inclusion of the additional C 1s component in the core level fits is shown to lead to solution of a long standing problem regarding quantitative analysis based on the C 1s peak intensities. Applicability of the MS approach to such practical problems in XPS together with its simplicity and intuitiveness make this approach particularly attractive for the experimental chemist.