Dual beam spectrometer

The dual beam spectrometer used a Bomem Michelson 110-E equipped with a KBr beamsplitter and midrange (650 cm-V) MCT (measured D = 2 x 1010) detector (details to be published). Spectra were recorded at 4 cm-1 resolution and each scan required 1 second to collect. Data collection and processing were performed as above. 

Figure 9. Dual-beam spectrometer optical layout as used for GC-IR measurements. (Reproduced from reference 28, by permission of the American Chemical Society, copyright 1978).

For many chemists, the most familiar IR spectrometer is the dual beam instmnient that covers the region 900-... 

Like much instrumentation working in the IR/visible/UV region of the spectrum, most modern UV/visible spectrometers are of the dual-beam type, since this eliminates fluctuations in the radiation source. The principle of this has been described in detail in Section 3.2. Radiation from the source is split into two by a beam splitter, and one beam is passed through the sample cell (as in a single beam instrument). The other beam passes through a reference cell, which is identical to the sample cell, but contains none of the analyte... 

The laser hres at f = 0 and causes an increase in absorbance in the sample as a consequence the intensity of light reaching the detector decreases. While laser photolysis systems are normally single-beam spectrometers, in fact they behave as dual-beam instruments. The reference beam is separated from the sample beam in time, rather than space. Thus, the reference signal is acquired before laser excitation and leads to Iq. The absorbance at time t in Figure 18.3 is given by Eq. 1 ... 

A Dual-Beam Photodiode Array Spectrometer System for Liquid Chromatographic Separation Methods Development... 

Dougherty TP, Heilweil EJ. Dual beam subpicosecond broadband infrared spectrometer. Optics Lett 1994 19 129-131. 

Hamm P, Wiemann S, Zurek M, Zinth W. A dual-beam sub-picosecond spectrometer for the 5-11 pm spectral region and its application to vibrational relaxation in the Sj state. In Barbara PF, Knox WH, Mourou GA, Zewail AH, eds. Ultrafast Phenomena IX. Berlin Springer-Verlag, 1994 152-153. 

Various types of neutron scattering can be utilized to extract data on structure and dynamics for novel catalytic materials. By selectively deuterating an SSZ-13 zeolite, Cheetham and others" used ND performed on the Dual Beam Neutron Spectrometer (DUALSPEC) diffractometer at the Chalk River Laboratories and found that two acid sites are present in the unit cell of the zeohte. INS can be used to probe the mechanism of the catalytic reaction by looking at the change in the vibrational modes of the adsorbed molecules on the surface. Lennon et alP found that the interaction of HCl with a ]-alumina catalyst results in the dissociative adsorption of HCl, in which the hydroxyl groups terminally bound to A1 are replaced by chlorine. INS spectra reveal an in-plane deformation mode, 5 (OH), that can be resolved into two bands located at 990 and 1050 cm. ... 

In most instruments, the radiant flux is modulated periodically. This can be achieved by modulating the current of the primary source or with the aid of a rotating sector (g) in the radiation beam. Accordingly, it is easy to differentiate between the radiant density emitted by the primary source and that emitted by the flame. Both single beam and dual-beam instruments (see also Fig. 77) are used. In the latter the first part of the radiation of the primary source is led directly into the monochromator, whereas the second part initially passes through the flame. In this way fluctuations and drift can be compensated for insofar as they originate from the primary radiation source or the measurement electronics. Furthermore, the spectrometer can be provided with equipment for a quasi-simultaneous measurement of the line and background absorption [253]. 

Fig. 77. Flame atomic absorption spectrometer. A. Single beam and B dual-beam system, (a) hollow cathode lamp (b) flame (c) monochromator (d) rotating mirror ...

Hoffmann H, Wright N A, Zaera F and Griffiths P R 1989 Differential-polarization dual-beam FT-IR spectrometer for surface analysis Talanta 36 125-31... 

Fig. 4.23. Combined absorption and fluorescence spectrometo device in a schematic representation. An automatic dual beam DMR 21-spectrometer and a single beam PMQII-photometer are used. The cell holder ZFM4 cornices both instruments.

Perkin-Elmer Corporation markets the PE-21 dual beam infrared spectrometer... 

Figure 9 Dual-beam basic configuration of a diode array spectrometer.

Figure 30. Flame atomic absorption spectrometer A) Single beam B) Dual-beam system...

A double-beam spectrometer consists of both sample and reference channels and measures both channels simultaneously. The separation of the light beam from the source is accomplished using a beam splitter so that approximately 50% of the source-emitted energy is divided to both sample and reference channels. The use of the dual-beam concept compensates for instrument instabilities inherent to all spectrometers. The resultant spectrum is the ratio of the sample and reference channels in transmission. As in the case of single-beam instruments, in practice the final spectrum from this device is given as... 

The Fourier transform spectrometer (FTS) is a dual-beam interferometer, which is most frequently of the Michelson type, as shown in Fig.6.32. If the arms of the interferometer have equal lengths the path difference between the two interferring beams would be 0. If the mirror is moved A/2 an optical path difference of A is introduced. For the case of monochromatic radiation and equally intense beams the intensity at the detector will be... 

In a spectrophotometer the absorption of a molecular sample (gas, liquid or solid) can be measured as a function of the wavelength. The absorption normally occurs in not too narrow bands and therefore a continuum light source can be used in connection with a spectral resolving apparatus, which is normally a grating monochromator but can also be a Fourier transform spectrometer [6.111,112]. Spectrophotometers based on grating monochromators are frequently of the dual-beam type, with one beam passing the sample cell and the other one a reference (empty) cell of the same type before the transmitted intensities are compared at the detector. The lay-out for such an instrument is shown in Fig. 6.66. 

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