Resonant secondary radiation

Melinger J S and Albrecht A C 1986 Theory of time- and frequency-resolved resonance secondary radiation from a three-level system J. Chem. Phys. 84 1247-58... 

Methods used to obtain conformational information and establish secondary, tertiary, and quaternary structures involve electron microscopy, x-ray diffraction, refractive index, nuclear magnetic resonance, infrared radiation, optical rotation, and anisotropy, as well as a variety of rheological procedures and molecular weight measurements. Extrapolation of solid state conformations to likely solution conformations has also helped. The general principles of macromolecules in solution has been reviewed by Morawetz (17), and investigative methods are discussed by Bovey (18). Several workers have recently reexamined the conformations of the backbone chain of xylans (19, 20, 21). Evidence seems to favor a left-handed chain chirality with the chains entwined perhaps in a two fold screw axis. Solution conformations are more disordered than those in crystallites (22). However, even with the disorder-... 

This assumes that the frequency of the radiation is less than the resonant frequency so that the dipole vibrates in phase with the field. According to electromagnetic theory [1], this oscillating dipole will serve as a source of secondary radiation (scattering) of amplitude... 

Table 2.1 summarizes some of the events that occur in radiation chemistry through the various stages. The earliest discernible time, obtained from uncertainty principle, AE At - fi, is 1CH7 s, which accounts for the production of fast secondary electrons with energy > 100 eV Times shorter than these are just computed values. It has been suggested that, following ionization in liquid water, the dry hole H20+ can move by exact resonance until the ion-molecule reaction H20+ + H20 — H30+ + OH localizes the hole. The... 

MECHANISMS OF SECONDARY REACTIONS. The primary processes involved in absorption of radiation in polymers lead to the expectation of free radical and ionic mechanisms for the secondary chemical reactions. Electron spin resonance (ESR) spectroscopy has proved extremely valuable for observation of free radical reactions in polymers, where various radicals are stabilized in the solid matrix at different temperatures. 

Spectroscopy produces spectra which arise as a result of interaction of electromagnetic radiation with matter. The type of interaction (electronic or nuclear transition, molecular vibration or electron loss) depends upon the wavelength of the radiation (Tab. 7.1). The most widely applied techniques are infrared (IR), Mossbauer, ultraviolet-visible (UV-Vis), and in recent years, various forms ofX-ray absorption fine structure (XAFS) spectroscopy which probe the local structure of the elements. Less widely used techniques are Raman spectroscopy. X-ray photoelectron spectroscopy (XPS), secondary ion imaging mass spectroscopy (SIMS), Auger electron spectroscopy (AES), electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy. 

A picture that emerges from the above considerations can be summarized as follows. In contrast to the initial suppositions LEEs, the most abundant secondary product of interactions between condensed matter and ionizing radiation, turned out to be important damaging factor towards DNA. LEEs are ca. 30 times more efficient in the DNA cleavage than photons of the same energy. The resonance nature of damage seems to be well documented. Core-excited and shape resonances localized... 

In 1998, Liu et al. introduced modifications to the 3919 sequence to reduce the width of fhe on-resonance suppression notch while moving the secondary notches further out. The two new pulses were termed W4 and W5 (Figure 9C). It is important to note that there is a typo in the first paragraph incorrectly stating that the 3919 uses 62a = 180°. The value in the abstract and the original 3919 paper is correct (i.e. 26a = 180°). Like the 3919 sequence, W5 involves a series of explicit pulses (i.e. 5) interspersed with delays that control the solvent suppression width and where the secondary suppression notches occur. It is important to remember that these types of suppression schemes have a net zero effect on solvent (solvent resonances are moved off the +Z-axis but return, while solute is inverted) so radiation damping can certainly cause problems. Additional power may be required. 

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