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Carbon K-shell NEXAFS (near edge x-ray absorption fine structure) spectra of oriented hydrocarbon chains in Langmuir–Blodgett (LB) monolayers were measured and used to study the orientation of these molecules. The LB monolayers were assembled from arachidic acid or cadmium or calcium arachidate on the oxidized Si(111) surface. The observed NEXAFS resonances are assigned to transitions to excited states which are localized on individual CH2 groups or C–C bonds. From a detailed analysis using curve-fitting techniques of the angular dependence of the various spectral peaks, the hydrocarbon chains of the cadmium arachidate monolayer is estimated to lie within 15° of the surface normal, the hydrocarbon chains of the calcium arachidate monolayer is estimated to be tilted by 33±5° from the surface normal, while the arachidic acid monolayer is not ordered at all. The determined chain orientations are discussed in terms of a microscopic model involving lateral interactions between the zig–zag hydrocarbon chains.

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The quantitative analysis of the near-edge region of K-shell excitation spectra of free, chemisorbed, condensed, and polymeric molecules is undertaken using curve fitting procedures. The deconvolution of both x-ray absorption (NEXAFS) and electron impact near-edge excitation spectra is considered. Among the topics discussed are the line shape of resonances in the near-edge region, the line shape of the continuum steps, physical interpretations for the line shapes, and parameters describing core excitation spectral features, and background corrections for NEXAFS spectra. The goal of the work is to establish systematic procedures for analyzing near-edge spectra which allow peak positions to be consistently determined, and enable peak areas to be reliably obtained so that, e.g., the orientation of molecules can be determined from NEXAFS spectra. A more quantitative understanding of the features in near-edge spectra will also aid development of an understanding of the physical events underlying a near-edge spectrum.