Microwave region

Microwave spectroscopy began in 1934 with the observation of the -20 GHz absorption spectrum of ammonia by Cleeton and Williams. Here we will consider the microwave region of the electromagnetic... 

In the microwave region tunable monochromatic radiation is produced by klystrons, each one being tunable over a relatively small frequency range, or a backward wave oscillator, tunable over a much larger range. Both are electronic devices. Absorption experiments are usually carried out in the gas phase, and mica windows, which transmit in this region, are placed on either end of the absorption cell, which may be several metres in length. Stark... 

In practice, what is measured experimentally is not energy but frequency, in the millimetre wave and microwave regions, or wavenumber, in the far infrared. Therefore we convert the energy levels of Equation (5.10) to what are known as term values F J) having dimensions of either frequency, by dividing by h, or wavenumber, by dividing by he, giving... 

Most linear polyatomic molecules have smaller B values and therefore more transitions tend to occur in the millimetre wave or microwave regions. Figure 5.4 shows a part of the microwave spectrum of cyanodiacetylene (H—C=C—C=C—C=N) which has such a small B value (1331.331 MHz) that six transitions with J" = 9 to 14 lie in the 26.5 to 40.0 GHz region. 

The word laser is an acronym derived from light amplification by the stimulated emission of radiation . If the light concerned is in the microwave region then the alternative acronym maser is often used. Although the first such device to be constructed was the ammonia maser in 1954 it is the lasers made subsequently which operate in the infrared, visible or ultraviolet regions of the spectrum which have made a greater impact. 

Two-photon absorption has been observed in the microwave region with an intense klystron source but in the infrared, visible and ultraviolet regions laser sources are necessary. 

Microwave power and its effect on the electrode/electrolyte interface, 439 Microwave region, Hall experiments, 453 Microwave spectroscopy, intensity modulated photo currents, 508 Microwave transients for nano crystalline desensitized cells, 514 Microwave transmission, as a function of magnetic field, 515 Minority carriers... 

Self-Test 1.3A In 1965, electromagnetic radiation with a maximum at 1.05 mm (in the microwave region) was discovered to pervade the universe. What is the temperature of empty space ... 

For a polar molecule (/xo 0) the first term on the far right is nonzero only if the initial and final vibrational states are the same, viz. v = u. This case applies to the pure rotational spectra of gaseous molecules, as observed in the microwave region. The second term in Eq. (98) applies to vibrational transitions. The matrix elements of interest are (t> jc u), which are given by... 

Chemical reagents are primarily concerned with dielectric liquids or solids. For metal oxides such as ferrites, however, magnetic losses occur in the microwave region. As for a dielectric material, a complex magnetic permeability is defined as given by Eq. (16) ... 

Microwave spectroscopy The study of the interaction of microwave radiation with the rotational motion of a molecule. Microwave transitions are not restricted to molecules and can occur in atoms whenever the separation between the energy levels is in the microwave region of the spectrum. 

The method of paramagnetic resonance absorption makes use of the precession of the spinning impaired electron when it is placed in a magnetic field. This precession gives rise to absorption of radiation in the microwave region. The frequency at which the absorption takes place is given by the expression... 

When a Rydberg atom reduces its principal quantum number by one unit, when emitting a photon, the light is in the microwave region of the electromagnetic spectrum. With this radiation isolated Rydberg atoms can be observed in interstellar space, where interatomic collisions are rare. Atoms with n up to 350 have been observed by radio astronomical methods. 

This frequency is on the long wavelength side of the microwave region. 

The energies of rotation are quite small, so we require photons of relatively low energy to photo-excite between rotational quantum levels. For this reason, the spacings between rotational energy levels correspond to transitions in the far infrared and microwave regions of the electromagnetic spectrum. 

Rotational transitions from one state to another (e.g., Jo-Ji) require the least energy and these transitions usually occur in the microwave region of the spectrum. The energy of microwaves ranges from 156 to 325 J. Microwave spectra tend to have very sharp peaks. 

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