Raman spectroscopy melting transitions

A series of other condis crystals are the larger cyclo-alkanes, analyzed by Gross-mann 171). Figure 23 illustrates the transition behavior of cyclotetracosane and cyclo-hexanonacontane. The melting transition of cyclotetracosane has only about 1/4 the heat of transition at the disordering to the condis phase. The condis phase has a much higher symmetry and fewer X-ray diffraction lines. Infrared and Raman spectroscopy indicate that practically no additional conformational isomers are introduced on... 

IR Spectroscopy. The observation of a solid-solid phase transition in PDHS at the temperature of the UV thermochromic transition generated interest in the nature of the polymer chain conformation at temperatures above or below this critical temperature. A number of techniques have been used to study the solid-state structures of PDHS. Rabolt et al. (25) used IR spectroscopy to monitor the conformational behavior of the alkyl side chains of PDHS and Raman spectroscopy to follow that of the backbone. The IR spectrum of PDHS at +30 °C (Figure 9) consists of sharp, intense bands. When the film of PDHS is heated to +100 °C, the sharp deformation bands typical of a highly ordered hydrocarbon chain become broad and less intense, similar to the behavior observed in the IR spectra of n-alkanes at temperatures above the melting temperature. The data refiect conformational disorder in the side chains at temperatures above the +40 °C transition. After... 

In this section we discuss the change that occur in the melting of DNA and RNA. The term melting is used to refer a thermally induced transition of a double-helical nucleic acid from an ordered double helix to a disordered state. Native RNA is usually single stranded, but it folds back on itself to form double helical sequences. Raman spectroscopy does not appear to be sensitive to the tertiary structure of RNA, but it can tell what fraction of the RNA is in double-helical form. ... 

Orientation measurements have also been implemented for in-situ analyses of PP. The orientation and relaxation kinetics of melts in shear flows have been studied by IR spectroscopy in a rheometer. In another example, the orientation in the transition front of the neck during tensile deformation has been analyzed by Raman microspectroscopy. This last example is a natural link to studies of samples subjected to mechanical stress. 

Next, we study the temperature-dependent infrared and Raman spectra of Cl9 through phase transition (T ) (T = 22.8 °C) and melting (T ,) (T, = 32 °C). We first focus on the spectroscopy of C19. Each experimental observation is labeled and will be included in the overall analysis. In the IR spectrum ... 

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