Typical transmission spectra

For GaAs, R 0.3 over a wide range of wavelength, so that a d l ln(0.5/T). Note that E2exp( — lad) < R2 0.09 therefore, our above approximation is fairly good, even for a = 0. Martin and co-workers (1979) have used absorption measurements at 1.34 fim to determine the Cr concentration in GaAs. Typical transmission spectra are shown in Fig. 4 for a sample doped with... 

Fig. 24. The wavelength of the Bragg reflection, 2, of circularly polarized light shown as a function of temperature for (R)-l-methylheptyl 4 -(4-n-tetradecyloxyphenylpropioloy-loxy)biphenyl-4-carboxylate (14P1M7). The inset shows a typical transmission spectra for right circularly polarized light (solid line), and left circularly polarized light (dashed line) at 92.8 °C...

FIGURE 18.2 Typical transmission spectra in the IR region. The ordinate in each diagram is 0%-100% transmission. The incompletely hydrolyzed sample of polyfvinyl acetate) illustrates the additivity of spectra. (Data from Nyquist, R. A., Infrared Spectra of Plastics and Resins, 2nd edn., Dow Chemical Co., Midland, TX, 1961.)... 

The ATR technique is a commonly used infrared internal reflection sampling technique. It samples only the surface layer in contact with the ATR element the sampling depth probed is typically of the order of 0.3-3 pm [1]. Unless software corrected, compared with a transmission spectrum, the relative intensity of bands within an ATR spectrum increase in intensity with decreasing wavenumber. Several FTIR instrument companies now supply "ATR-correction" software developed to correct for the different relative intensities of bands observed between ATR and transmission spectra, so that ATR spectra can be more easily compared to and searched against transmission spectra. 

Figure 5.2 shows a typical IR spectrum for a Rh system in aqueous AcOH obtained from a transmission cell at 180 °C and pressurized to about 30 bar vdth CO. Peaks due to [Rh(CO)2l2] are indicated. 

Figure 1. Typical CL spectrum from enstatite in the enstatite chondrite ALHA 77295. Peak positions for this and other spectra are estimated by eye and the spectra are not corrected for instrumental transmission.

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. 

Here s what a typical IR spectrum actually looks like notice that the wavenumber scale runs from high to low but also that absorption maxima are shown upside down (IR spectra plot transmission )—you might say that IR spectra are upside down and back to front. If you look carefully you will also see that the scale changes in the middle to give more space to the more detailed right-hand half of the spectrum. 

Commonly, excited singlet states have very short lifetimes and can only be detected by means of femtosecond absorption spectroscopy. A typical case is illustrated in Fig. 1.24, which shows the differential transmission spectrum of MEH-DSB (see Chart 1.18). 

In the 1970s, HP-IR for homogeneous catalysis was generally carried out in modified autoclaves, using either transmission or reflectance cells to obtain the spectrum. Typical transmission cells require the use of suitable windows built into the autoclave body which can withstand both high pressures and chemical exposures (Figure 2). The autoclave sits within the body of the IR spectrometer, and can be connected to gas and liquid supplies as... 

This approach finesses the difficulties associated with strong water absorptions by simply eliminating water from the specimen. Typically 5-50 pL of liquid is spread on a suitable substrate and allowed to dry, and a transmission spectrum is acquired for the resulting film. In addition to eliminating the spectral interference of water. 

FIGURE 5. Typical AES spectrum of an oxidized aluminum surface, (a) d A ( )/d spectrum, (b) EN(E) spectrum. The factor of E is due to the transmission function of the analyzer. The common means of measuring peak intensity, peak-to-peak height (p-p), and peak-to-background height (p-b) are indicated. 

If a sample absorbs IR radiation at characteristic wavenumbers, it is capable of emitting radiation at these wavenumbers. A thin sample of a material will emit radiation with a spectrum very similar to its absorption spectrum. By ratioing the emitted radiation from the thin film to that from a black body at the same temperature, an emissivity spectrum is obtained which generally has the appearance of an inverted transmission spectrum. Emission spectra used to be collected from samples heated well above r.t., typically to 40-100°C (to minimise sample degradation), with a black-body source (e.g. graphite) at the same temperature as a reference. With FTIR instruments, emission spectra can also be recorded at room temperature. 

Figure 8.5. Typical glitch on the baseline of a transmission spectrum. In this case the glitch is at 1020cm f Since the spectrum was measured with a data acquisition frequency of 5 kHz using a HeNe laser interferogram to trigger data acquisition, the glitch was caused by interference by a sinusoid of frequency 320Hz, possibly caused by a mirror vibrating at this frequency.

However, these analogues are actually hypothetical. The reason for this is that it is nearly impossible to obtain optical measurement components, such as the source and the detector, whose response to light across the visible spectrum is flat (or nearly so). However, this is not an impossible task and we find that an excellent match can be obtained to the transmission functions of 7.8.21., i.e.-those of the Standard Observer. This is typical for commercially available instruments. Now, we have an instrument, called a Colorimeter, capable of measuring reflective color. 

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