Single-beam

Block diagram for a single-beam fixed-wavelength spectrophotometer with photo of a typical instrument. 

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

Atomic absorption spectrophotometers (Figure 10.37) are designed using either the single-beam or double-beam optics described earlier for molecular absorption spectrophotometers (see Figures 10.25 and 10.26). There are, however, several important differences that are considered in this section. 

In the process of performing a spectrophotometric determination of Ee, an analyst prepares a calibration curve using a single-beam spectrometer, such as a Spec-20. After preparing the calibration curve, the analyst drops the cuvette used for the method blank and the standards. The analyst acquires a new cuvette, measures the absorbance of the sample, and determines the %w/w Ee in the sample. Will the change in cuvette lead to a determinate error in the analysis Explain. 

Procedure. The study can be carried out using either a manually operated single-beam spectrophotometer, or an automatic recording double-beam spectrophotometer. In both cases the wavelengths at which HMR and MR-exhibit absorption maxima are readily obtained from the spectra. 

Double-beam AA spectrophotometers are still marketed by instrument manufacturers. A double-beam system compensates for changes in lamp intensity and may require less frequent re-zeroing than a single-beam instrument. These considerations had more merit some years ago when hollow cathode lamps suffered from some instability. It should be noted, however, that the optical... 

Spectrographically standardised substances 830 Spectrophotometer cells for, 664 data presentation, 665 double-beam, 667 layout of instruments, 666, 667 operation of, 672 radiation sources for, 664 single-beam, 666... 

For large telescope apertures, Na LGS offer improve sampling of the atmospheric turbulence due to their much higher altitude. Single beam systems are now being developed for and deployed on 8-10 m class telescopes. Since resonant backscattering from the mesospheric Na layer is the method chosen for most LGS projects, we will concentrate mostly on this technique. 

The decomposition kinetics of the N-Br-amino acids was studied spectro-photometrically by following the fall in absorbance at the wavelength of the absorbance maximum of the N-bromoamino acid, in a Milton Roy Spectronic 3000 Array or a Beckman DU65 single-beam spectrophotometer, both equipped with a cell carrier thermostated to within 0.1 °C by water flow. Kinetic experiments were initiated using a hand-driven HI-TECH SFA-12 Rapid Kinetics Accessory with a 1.00 cm flow cell. 

Fig. 3 Single beam IR transmission spectra of a single-crystal of orthorhombic Sg at two polarizations (hiu parallel to crystal c axis, l 2u+ 3u perpendicular to c) showing the strong absorption of the IR active vibrations V4 and Vg (resolution 2 cm ), after [105]. Sample thickness 450 pm...

Ashkin, A. (1992) Forces of a single-beam gradient laser trap on a dielectric sphere in... 

J. E. and Chu, S. (1986) Observation of a single-beam gradient force optical trap for dielectric particles. Opt. Lett., 11, 288-290. 

Sheik-Bahae, M., Said, A. A. and Van Stryland, E. W. (1989) High-sensitivity, single-beam ri2 measurements. Opt. Lett., 14, 955-957. 

Figure 45.2 ATR single beam spectmm of a catalyst thin-film on ZnSe crystal under argon upon UV-irradiation (a) P Ti02 catalyst, (b) Pd/AbOs catalyst, and (c) Au/T102 catalyst difference spectra reveals the background shift on (d) Pd/Ti02 catalyst, (e) Pd/Al203 catalyst, and (f) Au/Ti02 catalyst.

Figure 52.1. Single beam IR spectra of the Pl/Ti02 catalyst on the DRIFT cell before and after introducing ethanol, and during UV illumination.

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