Water vibrational absorption

Apart from molecular vibrations, also rotational states bear a significant influence on the appearance of vibrational spectra. Similar to electronic transitions that are influenced by the vibrational states of the molecules (e.g. fluorescence, Figure 3-f), vibrational transitions involve the rotational state of a molecule. In the gas phase the rotational states may superimpose a rotational fine structure on the (mid-)IR bands, like the multitude of narrow water vapour absorption bands. In condensed phases, intermolecular interactions blur the rotational states, resulting in band broadening and band shifting effects rather than isolated bands. 

The extinction features at energies where water is transparent are rapidly squelched in the ultraviolet as the onset of electronic transitions greatly increases bulk absorption. In the infrared, however, vibrational absorption bands in water are carried over into similar bands in extinction (dominated by absorption if a A) by a water droplet. Unlike MgO there are no appreciable spectral shifts in going from the bulk to particulate states. The reason for this lies in the strength of bulk absorption and will be discussed more thoroughly in Chapter 12. 

Since water is a weak Raman scatterer, Raman spectra of samples in aqueous solution can be obtained without major interference from water vibrations. Thus, Raman spectroscopy is ideal for the studies of biological compounds in aqueous solution. In contrast, IR spectroscopy suffers from the strong absorption of water. 

How does water vibrate around the hydrated electron What is the effect of these vibrations on the absorption, electronic, and... 

Losada M, Tran H, Xu Y (2008) Lactic add in solution investigations of lactic acid selfaggregation and hydrogen bonding interactions with water and methanol using vibrational absorption and vibrational drcular dichroism spectroscopies. J Chem Phys 128 014508-1-014508-11... 

Yang S, Cho M (2009) Direct calculations of vibrational absorption and circular dichroism spectra of alanine dipeptide analog in water quantum mechanical/molecular mechanical molecular dynamics simulations. J Chem Phys 131 135102-1-135102-8... 

Fig. 14.2 Absorption spectra of liquid water (Data from http //www.lsbu.ac.uk/water/vibrat.html http //omlc.ogi.edu/ spectra/water/rndex.html http //en.wildpedia.oig/wild/Electromagnetic absorptionJby water)...

Because the high attenuation of PMMA is caused by overtones of the C-H vibrational absorption, the most effective method for obtaining a low-loss POF is to substitute all the hydrogen atoms with heavier atoms such as fluorine, which helps to avoid the water absorption problem mentioned above. The replacement of hydrogen with fluorine also improves the thermal stability, chemical resistance, and electrical properties of POFs. The size of the fluorine atom allows the formation of a uniform and continuous sheath around the carbon-carbon bonds and protects them from attack, thus imparting heightened chemical resistance and stability to the molecule. 

The attenuation loss of this poly-(5F3DSt) core optical fiber is shown in Figure 7.9 along with that of PS-dg core POF. Absorption loss due to aromatic CH vibrations have almost disappeared and the loss in the near IR region is composed of residual aliphatic CH vibrations and CD vibrations. In the 850 nm region, an attenuation loss of 174 dB/km is obtained. The attenuation loss of the poly-(5F3DSt) core optical fiber before and after water vapor absorption reveals that the fiber exhibits no OH... 

IR spectra obtained from An promoted catalysts are presented in Fig.l. The chemical composition of the silica aerogel is characterized by the following set of absorption bands 470, 808, 1100, and 1640 cm. Bond vibrations at 1100 cm are Si-O-Si asymmetric stretching vibrations. Absorption bands at 808 and 470 cm can be assigned to bending vibrations of Si-O-Si and O-Si-O gronps. A weak absorption band at 1640 cm appears because of the presence of adsorbed water on the surface of the samples. 

Polyatomic molecules vibrate in a very complicated way, but, expressed in temis of their normal coordinates, atoms or groups of atoms vibrate sinusoidally in phase, with the same frequency. Each mode of motion functions as an independent hamionic oscillator and, provided certain selection rules are satisfied, contributes a band to the vibrational spectr um. There will be at least as many bands as there are degrees of freedom, but the frequencies of the normal coordinates will dominate the vibrational spectrum for simple molecules. An example is water, which has a pair of infrared absorption maxima centered at about 3780 cm and a single peak at about 1580 cm (nist webbook). 

The UV spectra of quinoxalines have been examined in several solvents. In cyclohexane, three principal absorptions are observed (Table 2). In hydroxylic solvents the vibrational fine structure disappears and in methanol or water the weak n- ir transitions are obscured by the intense ir->ir transition (79HC(35)l). 

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