Measurement reference beam

There is supporting evidence in the literature for the validity of this method two cases in particular substantiate it. In one, tests were made on plastics heated in the pressure of air. Differential infrared spectroscopy was used to determine the chemical changes at three temperatures, in the functional groups of a TP acrylonitrile, and a variety of TS phenolic plastics. The technique uses a film of un-aged plastic in the reference beam and the aged sample in the sample beam. Thus, the difference between the reference and the aged sample is a measure of the chemical changes. 

The cancellation of gas phase spectral features using the "half plate design Is far superior to methods Involving a second gas cell placed In the reference beam. This Is because the gas density and Its rotational state population will differ In the two cells for different sample (and therefore gas) temperatures. For high sensitivity measurements, these effects can be difficult to handle using two cells. 

The light from the infrared source C is made to split into two beams one of which passes through the sample i.e., the sample beam) while the other caters as the reference beam. This sort of double-beam arrangement facilitates in measuring difference in intensities between the two beams at each wavelength,... 

An alternative to observing sample and reference together at high resolution involves the use of a double-beam mass spectrometer such as the AEI MS-30. If closely spaced mass multiplets need not be resolved, one can determine the exact mass of each peak in the spectrum at resolutions of 1500, the computer acquiring data from the independent sample and reference beams simultaneously (226). Thus, source conditions can be optimized for compound and reference at the higher sensitivities available at lower resolutions, the mass measuring accuracy still being in the order of 10 ppm. This is possible, since if mass doublets are not involved, the centroid of a peak is as well defined at resolution 1500 as at 10,000. 

Using a matched pair of cells, place the lowest standard in the reference beam, and measure the absorbance of the other standards at 420 nm. Plot the standard curve relating absorbance to known concentration. 

The mixing of the signal and reference beams results in a measured intensity that incorporates a strong constant contribution from the reference field and a... 

Infrared spectra were recorded on the resist film spun onto a silicon wafer using a JASCO IR-810 spectrometer equipped with a JASCO BC-3 beam condenser or a JASCO A-3 spectrometer. In the measurements on the latter spectrometer an uncoated silicon wafer was placed in the reference beam in order to balance the silicon absorption band. The subtraction between the spectra was carried out on a built-in micro-processor attached to the IR-810 spectrometer, and the resulting difference spectrum was used to detect structural changes in the polymer molecule upon exposure. The subtraction technique was also used to balance the silicon absorption band. 

The direct measurement of the g(1,(x) can be achieved by either the interference between the scattered field and a reference beam (heterodyne) or the interference... 

Fig 1 Optical arrangement for measuring the velocity of a moving phase object using Schlieren Interferometry of Doppler-shifted laser light. A is the Doppler-shifted beam, and B is the reference beam... 

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. 

Spectra were run on a Perkin-Elmer model 125 grating spectrophotometer at room temperature, ignoring the heating effect of the IR beam. Reference beam attenuation was used. The spectral slit width was less than 3 cm-1 in the region 1600-1400 cm-1. Optical density measurements were carried out as previously described (19). 

In order to determine the chlorophyll and carotenoid content of your extract, you must measure the absorbance at several wavelengths, 661.6, 644.8, and 470 nm. If you are using a single-beam spectrophotometer, use a cuvette of acetone to zero the instrument at each wavelength. A double-beam instrument should have a cuvette of acetone in the reference beam and the acetone extract solution in the sample beam. If desired, it is instructive to obtain a complete spectrum of the extract in the range 400-700 nm. This can be compared to the spectrum obtained for each of the individual pigments in part D. 

Figure 11. Measured molecular-beam distribution from equation 25. Open circles represent the measured values. The solid curve represents the predicted distribution. (Reproduced with permission from reference 1. Copyright 1985 American Institute of Physics.)...

The cell has an optical capability of 2.5 m, using 12 transversals. When applied to CO2, however, the absorption coefficient (ac) is of sufficient size to allow measurements using an 0.5 m (4 transversals) path. Due to the magnitude of ac, a large difference in intensity develops as the beam passes through the cell. Maximum detection and amplification efficiency can only be achieved when the intensity levels of the sample and reference beams are approximately the same. To help balance the intensity levels, the mirror coatings (multi-layer silicon/silicon dioxide) have been optimized to pass the sample beam (99 percent reflectance at 4.3 pm) and partially attenuate the reference wavelength (95 percent... 

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