Curve fitting analysis of near-edge core excitation spectra of free, adsorbed, and polymeric molecules

Abstract

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.

Adsorption Geometry Determines Catalytic Selectivity in Highly Chemoselective Hydrogenation of Crotonaldehyde on Ag(111)

“…Experimental details relevant to the synchrotron experiments are provided elsewhere [13][14][15] and the NEXAFS data were processed by standard methodology. 16,17 XPS binding energies were corrected for monochromator error and adsorbate coverages were calibrated by continuously monitoring the C 1s XPS signal during exposure of the sample to each adsorbate, the monolayer point being identified by shifts in the binding energies of the peak maxima.…”

Angular dependent NEXAFS study of the molecular orientation of PTCDA multilayers on Au (111) surface

“…The O K-edge NEXAFS spectra were performed in total electron yield (TEY) mode with a photon energy resolution of 500 meV. To eliminate the effect of fluctuation of the incident beam intensity, all spectra were first normalized to the incident beam flux (monitored by refocusing mirror I 0 ) and later normalized to the same edge jump [18].…”

Aging induced changes on NEXAFS fingerprints in individual combustion particles

“…The solid and open symbols represent the unprocessed and aged soot particles, respectively. of the broad variety of carbon species present in soot (Outka and Stohr, 1988). The spectra were normalized to the area of the whole spectrum.…”

“…Each spectrum represents the average of several individual particles, using the image-stacks described in the experimental section. Specific chemical species were quantified from the spectra by fitting with Gaussian functions representing characteristic near-edge resonances (Outka and Stohr, 1988), using resonance positions adopted from Hopkins et al (2007). The peak energies were fixed at the C 1s→ π transition of aromatic carbon in benzoquinone (quinone-C, 284.2 eV), of unsaturated carbon (aromatic-C, 285.2 eV), of phenolic or ketone carbon (phenol-C, 286.7 eV), of carboxylic carbon (carboxyl-C, 288.3 eV), of carbonyl carbon (carbonyl-C, 290.5 eV) and at the C 1s→ σ transitions of aliphatic carbon (aliphatic-C, 287.4 eV), which overlaps with the C 1s→ π transition of aromatic carbonyl groups, of Oalkylic carbon (289.5 eV), and of aliphatic/aromatic carbon (aliphatic/aromatic-C, 292 eV).…”