Microwave magnetic-field components

The simplest coherence experiment in the case of single spin EPR, is a (transient) nutation experiment [22]. In this experiment the spin is forced to precess perpendicular to the direction of the microwave magnetic field component in the rotating frame. This is equivalent to a periodic modulation of the population probability of the two T] sublevels in resonance with the microwaves. This periodic modulation leads to a change in the lifetime of the Ti state and thus to a corresponding modulation of the average fluorescence intensity. 

In magnetic fields with B0>0.1 T only two levels, SQi and SQ2 generally contain a singlet component S, which defines the transition of a pair to a final singlet state. These transitions cause partial emptying of the SQi and SQ2 levels. Microwave magnetic field stimulates mainly transitions from the quintiplet levels Q+i and Q i to the SQi and SQ2 ones (Fig. 5), whose occupancy increases. Since the total rate constant (1) defined as... 

Figure 24. The loop-gap resonator showing the principle components (a, loop b, gaps c, shield d, inductive coupler) and the critical dimensions (Z, resonator length r, resonator radius R, shield radius t, gap separation W, gap width). The sample is inserted into the loop a through the coupler, d. The microwave magnetic field in the loop is parallel to the axis of the loop. From [291], with permission.

The degree of interaction between the microwave electric and magnetic field components with the dielectric or magnetic material determines the rate at... 

Among the various green technologies, microwave chemistry is of significant importance. Microwaves have both electric and magnetic field components. They operate in a frequency range between... 

Microwaves are electromagnetic radiations lying between radio wave frequencies and infrared frequencies (between 0.3 and 300 GHz). These are produced by a magnetron, which consists of a thermionic diode having an anode and a directly heated cathode. Microwaves contain an electric and a magnetic field component. It is the interaction between the electric field component and the matter that generates the heat through two mechanisms. ... 

The basic features of an epr spectrometer are shown in Figure 2.95. The microwave source is a Klystron tube that emits radiation of frequency determined by the voltage across the tube. Magnetic fields of 0.1 — 1 T can be routinely obtained without complicated equipment and are generated by an electromagnet. The field is usually modulated at a frequency of 100kHz and the corresponding in-phase component of the absorption monitored via a phase-sensitive lock-in detector. This minimises noise and enhances the sensitivity of the technique. It is responsible for the distinctive derivative nature of epr spectra. Thus, the spectrum is obtained as a plot of dA/dB vs. 

Microwave radiation, as all radiation of an electromagnetic nature, consists of two components, i.e. magnetic and electric field components (Fig. 1.3). The electric field component is responsible for dielectric heating mechanism since it can cause molecular motion either by migration of ionic species (conduction mechanism) or rotation of dipolar species (dipolar polarization mechanism). In a microwave field, the electric field component oscillates very quickly (at 2.45 GHz the field oscillates 4.9 x 109 times per second), and the strong agitation, provided by cyclic reorientation of molecules, can result in an... 

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