Transmittance, vibrational spectroscopy

This technique is the most widely utilized variant of surface vibrational spectroscopy and is accomplished by simply measuring the transmittance of infrared radiation passing through the sample. A penetration of ca. 10 monolayers is necessary in order to achieve a satisfactory signal/noise ratio. For in-situ experiments zeolites are applied as pressed disks with a thickness of about 5-8 mg/cm. Due to the strong framework vibrations there is a nearly complete... 

Spectroscopy certain molecular vibrations are absorbed and the transmittance of the infrared light... 

Infrared and Raman spectroscopy, coupled with optical microscopy, provide vibrational data that allow us to chemically characterise geochemical sediments and weathered samples with lateral resolutions of 10-20 pm and 1-2 pm respectively. Fourier transform infrared spectroscopy involves the absorption of IR radiation, where the intensity of the beam is measured before and after it enters the sample as a function of the light frequency. Fourier transform infrared is very sensitive, fast and provides good resolution, very small samples can be analysed and information on molecular structure can be obtained. Weak signals can be measured with high precision from, for example, samples that are poor reflectors or transmitters or have low concentrations of active species, which is often the case for geochemical sediments and weathered materials. Samples of unknown... 

The 1-mm-fhick transparent sample possessed a transmittance of about 60 % at 600 nm. According to Raman spectroscopy, it was found that there were some phonon vibrational shifts, which implied that minor secondary phases could be have introduced due to the contamination from the milling media. Such minor secondary phases could not be detectable by using XRD, because of their very small quantity. This result further indicates that special carefulness is important when processing transparent ceramics. 

The chemical modification of the clay can be studied with the help of Fourier transform infrared spectroscopy (FTIR). In FTIR spectra of co-treated and mono-treated clays, the transmittance bands at 2922 cm and 2854 cm correspond to asymmetric and symmetric stretching vibration of methylene groups (Figure 9.5). Carbonyl stretching shows a band at 1715 cm. Both the mono-treated and co-treated montmorillonites have the absorbance bands of methylene, which is due to the successful tethering of octodecylammonium and aminoimdecanoic acid to the clay platelets [24]. 

Several available FTIR techniques such as attenuated total reflection [5-7] have been utilized for coatings hardened on a metal surface, diffuse reflectance [8] for ultra-thin films, and transmittance [9, 10] for clear or transparent coatings. The FTIR is useful for determining parameters such as residual porosity and molecular bonding. If used in concert with a microscope, excellent spatial resolution can be obtained. Hasik et al. [11] studied a polysiloxane-silsesquioxane system with FTIR spectroscopy while developing SiCO ceramic. The authors noticed the transformation in vibration bands, in their material, as a function of chemical compositions and temperature. A quartz crystal microbalance and reflection-absorption infrared spectroscopy (RAIR) was used to study silane reaction over oxidized aluminum surface [12]. 

---