Microwave technologies

Microwave spectroscopy is generally defined as the high-resolution absorption spectroscopy of molecular rotational transitions in the gas phase. Microwave spectroscopy observes the transitions between the quantised rotational sublevels of a given vibrational state in the electronic ground state of free molecules. Molecular 

The use of microwaves for heating chemical reactors has increased dramatically over the past decade [428]. 

After Walker et al. [430]. Reprinted with permission from P.J. Walker et al., in Microwave-Enhanced Chemistry (H.M. Kingston and S.J. Has-well, eds), American Chemical Society, Washington, DC (1997), pp. 55-121. Copyright (1997) American Chemical Society. 

The microwave technique is widely applied to process polymer materials, e.g. in microwave cure [429], Microwave processing is a developing technology. 

Applications of microwave radiation relevant to the analytical chemist cover  

---

High Frequency Dielectric Strength. Dielectric strength at high frequency is important in microwave power uses such as radar (see Microwave technology). Because SF has zero dipole moment, its dielectric strength is substantially constant as frequency increases. At 1.2 MHz, SF has... 

Microwave Ferrites. Microwave devices employing ferrites make use of the nonreciprocal propagation characteristics that are close to or at a gyromagnetic-resonance frequency at ca 1—100 GHz. The most important devices are isolators and circulators (see Microwave technology). 

The field of microwave technology is expected to increase as better and cheaper microwave systems are developed. In particular, uses for 5800 and 2450 MHz and the millimeter wave frequencies await the development of inexpensive efficient sources of power at those frequencies. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

Arsine is used for the preparation of gallium arsenide [1303-00-0] GaAs, (17), and there are numerous patents covering this subject (see Arsenic and ARSENIC alloys). The conversion of a monomeric arsinogaHane to gallium arsenide has also been described (18). GaUium arsenide has important appHcations in the field of optoelectronic and microwave devices (see Lasers Microwave technology Photodetectors). 

Dielectric and Microwave Dryers. Dielectric, also caEed radio frequency, dryers operate in the frequency range of 1—100 MHz. Microwave dryers in the United States operate at 915 MHz and 2450 MHz (see Microwave technology). As depicted in Figure 24, a dielectric dryer may consist of two... 

Microwave technology has also been extended to the preparation of 1,2,4-... 

---