Spectroscopic investigations supercritical fluids

Substantial evidence suggests that in highly asymmetric supercritical mixtures the local and bulk environment of a solute molecule differ appreciably. The concept of a local density enhancement around a solute molecule is supported by spectroscopic, theoretical, and computational investigations of intermolecular interactions in supercritical solutions. Here we make for the first time direct comparison between local density enhancements determined for the system pyrene in CO2 by two very different methods-fluorescence spectroscopy and molecular dynamics simulation. The qualitative agreement is quite satisfactory, and the results show great promise for an improved understanding at a molecular level of supercritical fluid solutions. 

Spectroscopic Investigations of Organometallic Photochemistry in Supercritical Fluids... 

Mixed solvents The addition of a small amount of a co-solvent to a supercritical fluid can increase solubilities of certain substances from several percent to several orders of magnitude (32.33.34.35). Spectroscopic data, which have been obtained recently, indicate that preferential solvation by a co-solvent contributes to the large increases. The co-solvents acetone, methanol, ethanol, and n-octane, were investigated by Kim and Johnston(36) using the solute phenol blue as a solvatochromic indicator. In Figure 7, it is apparent that the red shift (solvent strength) exceeds the value which is obtained from linear behavior, i.e. the concavity is positive. This means that the local concentration of co-solvent near the solute... 

Brennecke, J. R 1993. Spectroscopic investigation of reactions in supercritical fluids. A review. In Supercritical Eluid Engineering Science. Eundamentals and Applications, edited by E. Kiran and J. R Brennecke. Washington, DC American Chemical Society, p. 201. Brennecke, J. F., P. G. Debenedetti, C. A. Eckert, and K. P. Johnston. 1990. Letter to the editor. 

Maiwald, M. and Schneider, G.M. (1995) Necir-infrcired spectroscopic investigations on ph ise behavior and hydrogen-bonding of tu-heptanolactam in supercritical chlorotrifluoromethane, J. Supercrit. Fluids 8, 25-29. 

Tuma, D. (1999), Spectroscopic high-pressure investigations in near and supercritical fluids up to 180 MPa — Solubility and stability of anthraquinone dyestuff s and /3-Carotene in CO2, N2O, CCIF3, and SFe (in German), Doctoral dissertation, University of Bochum, Germany. 

Brennecke, J. E 1993, Spectroscopic investigations of reactions in supercritical fluids A review . In E. Kiran and J. F. Brennecke (eds.) Supercritical Fluid Engineering Science ACS Symposium Series. Washington ACS. 

THEORETICAL AND SPECTROSCOPIC STUDIES There have been a considerable number of papers which fall into this category. Metal carbonyl photochemistry in organic solvents is covered comprehensively in an article dealing with femtosecond transient absorption and preliminary resonance Raman spectroscopy Turner, Poliakoff and co-workers have continued their spectroscopic investigations of organometallic chemistry in supercritical fluids 14.15,16 gjga of exceptional potential. The... 

Numerous experimental studies have been conducted on solute-solvent interactions in supercritical fluid solutions. In particular, issues such as the role of characteristic supercritical solvent properties in solvation and the dependence of solute-solvent interactions on the bulk supercritical solvent density have been extensively investigated. Results from earlier experiments showed that the partial molar volumes 02 became very large and negative near the critical point of the solvent (4-12). The results were interpreted in terms of a collapse of the solvent about the solute under near-critical solvent conditions, which served as a precursor for the solute-solvent clustering concept. Molecular spectroscopic techniques, especially ultraviolet-visible (UV-vis) absorption and fluorescence emission, have since been applied to the investigation of solute-solvent interactions in supercritical fluid solutions. Widely used solvent environment-sensitive molecular probes include Kamlet-Taft jt scale probes for polarity/polarizability... 

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