Infrared reference beam attenuator

A Mutiple Internal Reflection Accessory for use with Perkin-Elmer infrared spectrophotometers was used to introduce the sample to the IR beam. To correct for losses in energy transmittance through the sample beam resulting from the use of the MIR Accessory, a comb-type reference beam attenuator was employed. A LFE Corpora-... 

For infrared analysis, each standard quartz filter or redeposited sample filter is cut in half with surgical scissors and placed on the 30 or desired angle setting of the MIR ccessory base. The IR is adjusted to a scan setting of 750 cm and the reference beam attenuator is used to bring the transmittance level to 90-l(j)0%. The filter is then scanned in duplicate from 900 to 700 cm. pie spectrum is recorded yn absorbance chart paper. 

For IR measurements the catalyst was compressed at 4 X 108 Pascal. The disc (18 mm diameter, 20-30 mg) was mounted in a quartz sample holder which was introduced in the adsorption/infrared cell (10). To avoid the reduction of the Pd(II) ions by hydrocarbons, the cell was grease free. Samples were activated according to treatment c. Spectra were recorded on a Perkin Elmer model 125 grating spectrometer. The reference beam was attenuated, and the instrument was flushed with air freed of H20 and C02. 

Carbon monoxide was introduced at 25° C under an equilibrium pressure around 50 torr. Infrared spectra were recorded on a Perkin-Elmer grating spectrophotometer model 125. The reference beam was attenuated, and the instrument was continuously flushed with air freed from C02 and water. 

Determining the Infrared Spectrum. To obtain the spectrum, slide the holder appropriate for the type of die that you are using into the slot on the infrared spectrophotometer. Set the die containing the pellet in the holder so that the sample is centered in the optical path. Obtain the infrared spectrum. If you are using a double-beam instrument, you may be able to compensate (at least partially) for a marginal pellet by placing a wire screen or attenuator in the reference beam, thereby balancing the lowered transmittance of the pellet. An FT-IR instrument will automatically deal with the low intensity if you select the "autoscale" option. 

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