Microwave analog technique

Figure 11.22 Schematic diagram of the microwave analog technique for measuring extinction by single oriented particles.

For various reasons the microwave analog technique has seen only intermittent use in the United States since its inception over 20 years ago. But recently there has been an upsurge of activity—a hopeful sign. Some of the most recent measurements have been reported by Schuerman et al. (1981). 

Microwave scattering is an important analog technique for investigating scattering of visible light by single nonspherical particles. Because of the ratio of about 105 between microwave and visible wavelengths, arbitrarily oriented... 

Another technique, called the microwave analog method, simulates the light scattering using microwave radiation [60, 61]. It takes advantage of the... 

As discussed in Chapter 6, in systems with more than one unpaired electron the ESR spectrum contains features that involve electron-electron coupling parameters analogous to the nuclear hyperfine parameters. In those types of samples the advantages of double resonance are carried out by employing the use of two different microwave frequencies, one fixed and saturating, and one variable frequency that searches for transitions. This technique is known as ELDOR (electron-electron double resonance).38,40,41,44 It has been used much less than ENDOR and usually requires custom-built equipment. 

A rapid reaction kinetic technique (time scale = 10-1000 ps) that typically uses a Van de Graff accelerator or a microwave linear electron accelerator to promptly generate a pulse of electrons at sufficient power levels for excitation and ionization of target substances by electron impact. The technique is the direct radiation chemical analog of flash photolysis and the ensuing kinetic measurements are accomplished optically by IR/visible/UV adsorption spectroscopy or by fluorescence spectroscopy. 

During the last few years the application of the techniques of microwave spectroscopy to these gas molecules has provided much precise information about their properties.28 It has been found87 that the observed values of the internuclear distances can be closely approximated by use of an equation analogous to Equation 13-12. The potential energy of the molecule, analogous to 13-10 for the crystal, is... 

Light and potential modulated microwave reflectivity measurements offer a novel approach to the study of the semiconductor electrolyte interface. Perturbation of the density of electrons and holes in a semiconductor influences the conductivity and hence the imaginary component of the dielectric constant at microwave frequencies. For small perturbations, the change ARm in microwave reflectivity depends linearly on the change in conductivity [27, 28, 75). The application of frequency response analysis to light modulated microwave reflectance is relatively new [30]. Although the technique is analogous to IMPS, it provides additional information. 

Based on all these considerations, we may take 9.5 T with a homogeneity of 3 X 10" as an upper limit of simple and economical operation. A magnetic field of 9.5 T corresponds to a frequency of approximately 270 GHz for a g = 2 system. The techniques that we will develop in this chapter may be extended up to 1 THz we will limit our discussions and explicit examples to frequencies less than 300 GHz, where the analogies to conventional microwave techniques and components work best. 

Schlichthorl et al. [177] have used light modulated microwave reflectivity to derive the rates of interfacial electron transfer processes at the n-Si/electrolyte interface. In these measurements, the modulation frequency was constant, and the rate constants for charge transfer were derived from the potential dependent ARm response. Schlichthorl et al. [73] have extended the technique considerably by introducing frequency response analysis. The technique is therefore analogous to IMPS, although, as shown below, it provides additional information. 

Analogously to the LMR technique, Stark spectroscopy utilizes the Stark shift of molecular levels in electric fields to tune molecular absorption lines into resonance with lines of fixed-frequency lasers. A number of small molecules with permanent electric dipole moments and sufficiently large Stark shifts have been investigated, in particular, those molecules that have rotational spectra outside spectral regions accessible to conventional microwave spectroscopy [146]. 

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