Close cycle cryostat, matrix isolation

If one intends to use Ne or H2 as a host gas, one needs to take recourse to cryostats that are able to attain temperatures of 4 K or less. Until recently, ow cryostats, where liquid He is guided in a controlled fashion to the cold end, were usually required for such experiments. However, two-stage 4 K closed-cycle cryostats have recently become available that appear to obviate the need for liquid He. ° The author knows of two prominent matrix-isolation research groups who have been using such devices for a little while now and have no complaints about them. 

Two providers currently offer closed cycle cryostats for matrix isolation with 0.5-1 W of cooling power at 4 K. The first is Janis Reserach (http //www.janis.com/p-a4k.html), which uses hardware from Sumitomo, the other is Cryomech (http //www.cryomech. com/cryostats.html). 

The technique of matrix isolation has been shown to produce highly characteristic spectra of individual components of complex samples combination of MI spectroscopy with separation techniques promises to increase further the analytical capabilities of the technique. While our research to date has emphasized FTIR and molecular fluorescence spectrometry, MI as a sampling procedure is not limited to these two forms of spectrometry. For example, some interesting preliminary analytical results by MI Raman spectrometry recently have been described (32). It should also be stressed that the cryogenic procedures required for the vast majority of MI spectral studies are neither difficult nor unduly expensive except in very special cases, closed-cycle cryostats requiring no cryogenic liquids (and no prior experience in low-temperature techniques) are entirely satisfactory for MI... 

Cryostat. A cryostat designed for MBssbauer measurements of species isolated in a low temperature matrix was cooled down by a Cryomini D closed-cycle helium refrigerator (Osaka Sanso Kogyo Co. Ltd.) (Fig. 5). The sample holder in the cryostat was maintained at a desired temperature between 15 and 100 K by means of a 40-flanganin heater and a DTC-2 digital temperature controller... 

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