Short-Pathlength, High-Pressure Flow Cell for Static and Time-Resolved Infrared Spectroscopy Suitable for Supercritical Fluid Solutions Including Hydrothermal Systems

Abstract

An optical flow cell for high pressures and temperatures is described. The use of a novel window design allows for a precise, fixed optical pathlength that can be varied by use of spacers that range from a few micrometers to several millimeters. The cell pathlength is not affected by changes in pressure or temperature. The novel window design may be applicable to other high-pressure spectroscopic cells. The flow-cell design has a minimal sample dead volume, which is important for kinetic studies. The design eliminates the need for brazing or for a soft-sealing material for the optical windows, thereby minimizing the number of materials in contact with the sample. Using only diamond and platinum or platinum alloys as the corrosion resistant materials, the design is optimized for the study of aqueous solutions at high temperatures. Infrared spectra of an aqueous sodium tungstate solution up to 400?°C and 380 bar pressure are presented. Time-resolved infrared data are also presented for the ultraviolet photolysis reaction of ?-naphthoyl azide in supercritical carbon dioxide.