High-pressure, capillary x-ray absorption fine structure cell for studies of liquid and supercritical fluid solutions

A method is described to acquire x-ray absorption fine structure (XAFS) spectra of high-pressure liquid and supercritical fluid solutions. The technique employs a short length of fused-silica capillary tubing that has an inner diameter of 250 mu m and an outer diameter of 360 mu m. A hairpin bend is formed near the center of the capillary and the bend is then placed end-on directly in the focused x-ray beam. Fluorescence spectra were acquired in a 90 degrees geometry using a 13 element Ge detector. Demonstration XAFS spectra are reported for a Mn organometallic complex dissolved in subcritical and supercritical CO2. Although the maximum pressure of these studies was 160 bar, with slight modification, the method will be applicable to studies requiring pressures as high as 4 kbar. (C) 1996 American Institute of Physics.