Polarization IR beam

Reflection-Absorption IR spectroscopy (RAIRS) where the linearly polarized IR beam is specularly reflected from the front face of a highly reflective sample, such as a metal single crystal surface (Figure 3.1(a)). This is also sometimes referred to as IRAS (IR reflection absorption). The IR beam comes in at grazing angle (i.e. almost parallel to the surface), and although absorption bands in RAIRS have intensities that are some two orders of magnitude weaker than in transmission studies on... 

The SFG spectra discussed in the preceding sections were obtained in ppp-polarization combination (i.e., by detecting a p (parallel)-polarized SFG signal produced by a p-polarized visible and a p-polarized IR beam). This combination is typically used for adsorption/reaction investigations of metal surfaces because it produces the most intense adsorbate SFG signal (46,430). However, it is also possible to use other polarization combinations, for example, ssp (s ( senkrecht, i.e.. 

In a typical set-up (constructed as an accessory to be mounted in the sample compartment of a commercial FT spectrometer), infrared radiation is focused on the sample surface at a defined angle. The reflected beam is focused onto a detector. Irradiation with a polarized IR beam is often used. 

The FTIR/ATR technique is based on the fact that individual surfactant molecules, hemimicelles, monolayers, bilayers and spherical/cylindrical aggregates at the interface will have different average orientations of the alkyl chain with respect to the surface normal. Different average orientations would result in different absorptions of the plane-polarized IR beam, and can thus be used to identify the surfactant structures at the interface (11). 

For oriented single crystals there will generally be a difference in the absorption between two linearly polarized IR beams that are mutually orthogonal and orthogonal to the direction of propagations. The dichroic ratio is defined as... 

Figure 1-3. Schematic diagram of the dynamic infrared linear dichroism (DIRLDi experiment 23], A small-amplitude sinusoidal strain is applied to a sample, and submolecular level reorientation responses of chemical moieties are monitored with a polarized IR beam.

Figure 12.21 shows the time-dependent FTIR spectra of PCL melt on an oriented PE substrate at 59 °C with polarized IR beam aligned parallel or perpendicular to the PE chain direction. It is evident that when the polarized IR beam parallels to the chain direction of PE (see Figure 12.21a), the absorbance of conformational bands at 1295, 1245, and 1192cm increases significantly with time. On the... 

Figure 33 illustrates the schematic set up for a DIRLD spectroscopy experiment. A small-amplitude oscillatory tensile strain is applied to a sample, and the time-dependent fluctuations of IR dichroism signals corresponding to the dynamic reorientations of electric dipole transition moments associated with the molecular vibrations of various constituent chemical groups of the system induced by the applied strain are monitored with a pair of polarized IR beams oriented in directions parallel and perpendicular to the strain direction. Under a small-amplitude dynamic strain, the time-dependent dichroic difference can also be treated as the sum of a quasistatic component AA(v) and a dynamic component AA(v, t) induced by the strain s(t), similar to the stress response described in eqn [25]. 

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