Journal of Physical Chemistry B, Vol.119, No.45, 14373-14381, 2015
NEXAFS Sensitivity to Bond Lengths in Complex Molecular Materials: A Study of Crystalline Saccharides
Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, alpha-lactose monohydrate, anhydrous beta-lactose, cellulose) indicates that the precise determination of IPs and sigma* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10(-2) angstrom can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including noncrystalline systems without long-range order such as dissolved species in solutions, colloids, melts, and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas-phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modeling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value in that the sigma* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e., derived from ketoses and aldoses) as well as alpha from beta forms of otherwise identical saccharides.