High resolution x-ray fluorescence spectroscopy: A new technique for site- and spin-selectivity

X-ray spectroscopy has long been used to elucidate electronic and structural information of molecules. One of the weaknesses of x-ray absorption is that it is sensitivity to all of the atoms of a particular element. The resolution of K edge absorption is limited by the 1s core hole lifetime broadening. This thesis develops a new technique for enhancing the resolution and selectivity of the x-ray absorption spectrum.; By high resolution fluorescence detection, the chemical sensitivity of K emission spectra can be used to identify oxidation and spin states; it can also be used to facilitate site-selective X-ray Absorption Near Edge Structure (XANES) and site-selective Extended X-ray Absorption Fine Structure (EXAFS). The spin polarized features in K fluorescence could be used to generate spin selective XANES or spin-polarized EXAFS, which provides a new measure of the spin density, or the nature of the magnetic neighboring atoms. Finally, dramatic line-sharpening effects due to the coherence of absorption and emission processes allow observation of structure that is normally unobservable. All these unique characters can enormously simplify a complex x-ray spectrum.; The absorption and emission spectra by high resolution fluorescence detection are interdependent. The ligand field multiplet model has been used for the analysis of K{dollar}alpha{dollar} and K{dollar}beta{dollar} emission spectra.; First demonstration on different chemical states of Fe compounds has shown the applicability of site selectivity and spin polarization. Different interatomic distances of the same element in different chemical forms have been detected using site-selective EXAFS.; To make high resolution experiments on metalloproteins possible, a new spectrometer with higher efficiency has been developed. Some first metalloprotein results have shown that the strength of both site- and spin-selectivity could complement the structural information from other spectroscopies.; The first spin polarized EXAFS (SPEAXFS) of an antiferromagnetically coupled system using K{dollar}beta{dollar} detection is reported. Utilizing the internally referenced spin-up and spin-down transitions, the SPEAXFS effects are 2 order of magnitude larger than that of the method previously used, and it is suited for both antiferromagnetic systems as well as ferromagnetic systems.