A simple, sensitive method for measuring the refractive index of a liquid Am.A cryogenic refractometer is described. It enables preparation of liquefied samples and measurement of their refractive index at low temperatures (down to 20 K). The liquid sample can be a pure liquefied gas or a mixture. The composition of the liquid mixture can be estimated from the volume and pressure of each gas measured during the liquefying process. The determination of absolute values of the refractive index necessitates a calibration, therefore the accuracy is limited to 10 -3 index unit. Sensitivity and reproductibility are better (5 X 10 -4, and could be improved to 10 -4. The refractive index of pure liquid methane was determined at several temperatures (91-106 K) and 670 nm. The results obtained agree with the published data. The refractive index of mixtures of liquid methane and ethane, with and without dissolved nitrogen, was also determined at 94 K and 1.5 bar total pressure, for which conditions no data were previously available.
The site symmetry and magnitude of the crystal field splitting of metal atoms trapped in rare gas matrices may be determined by a combination of the temperature and magnetic field dependence of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD). General theoretical expressions are derived for the MCD and MLD considering the Zeeman effect and the matrix (i.e., crystal field) as perturbations on the free atom ‖JMJ〉 states. These expressions are applied to the observed MCD and MLD T- and B-saturation curves for Fe atoms isolated in krypton and xenon matrices in the range 0–1.5 T and 2.3–22 K. An octahedral crystal field model accounts well for all four independent sets of data (MCD vs B, MCD vs 1/T, MLD vs B2, and MLD vs 1/T2) for two different, isolated electronic transitions. A crystal field parameter of +0.06±0.05 cm−1 has been determined, corresponding to an overall electronic ground-state splitting of 3.2±2.5 cm−1. This splitting is less than the optical bandwidth and is shown to be consistent with previous studies of rare gas matrix-isolated Fe atoms by Mössbauer and laser-excited emission spectroscopies.
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