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Dense‐gas solvent‐solute clusters at near‐infinite dilution: EPR spectroscopic evidence
Author(s) -
Carlier Claude,
Randolph Theodore W.
Publication year - 1993
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690390516
Subject(s) - supercritical fluid , electron paramagnetic resonance , isobutane , chemistry , neopentane , dilution , cyclohexane , propane , binodal , analytical chemistry (journal) , thermodynamics , nuclear magnetic resonance , organic chemistry , molecule , physics , phase diagram , phase (matter) , catalysis
The nitrogen hyperfine splitting constant of ditertbutyl nitroxide radicals was measured with electron paramagnetic resonance spectroscopy at near‐infinite dilution in near‐critical and supercritical ethane, as well as in liquid propane, liquid isobutane, and several nonhydrogen bonding liquid solvents. While the measurements in the liquids are described well by the theory of McRae, large deviations from the liquid behavior are observed in supercritical ethane. The deviations are used as a measure of the effective local density of the solvent around the solute. At the two temperatures investigated, T r = 1.009 and T r = 1.084, the local density enhancement, defined as the ratio of local to bulk densities, exhibits a maximum of about 3 occurring around 1/2 the critical density. The maximum is removed well from the critical density, where the maximum of the isothermal compressibility is observed. Local density enhancements are short‐range effects and do not correlate well with the development of long‐range critical phenomena. Local density enhancement data in ethane are compared with the prewetting transition that has been observed in nearcritical ultrapure argon.