Isotropic film spectrum

Fig.7 FT-RAIRS spectrum of Rh2C04Cl2 on Ti02(l 10) [56], Measurements are carried out at (p=83 , and can be compared directly with the predictions of the model used for an isotropic film on an isotropic, non-absorbing substrate (Fig.6). The lines indicate the expectation values for the modes in the condensed phase.

In this section, only the optical constants of isotropic films determined by the multiwavelength approach in IRRAS will be discussed. The optical constants are assumed to be independent of the film thickness, and any gradient in the optical properties of the substrate (Section 3.5) is ignored. This undoubtedly lowers accuracy of the results. Anisotropic optical constants of a film are more closely related to real-world ultrathin films. At this point, it is worth noting that approaches to measuring isotropic and anisotropic optical constants are conceptually identical An anisotropic material shows a completely identical metallic IRRAS spectrum to the isotropic one if the complex refractive index along the z-direction for the anisotropic material is equal to that for the isotropic one [44]. However, to... 

The vibrational spectrum of benzene around 1000 cnf has also been measured. IQ. Benzene was physisorbed on a cooled copper substrate in the vacuum chamber. Figure 19 shows the transmission for several thicknesses of benzene and a prism separation of 3 cm. The thickness was determined from the measured transmission in transparent regions using Eg. (7). The solid curves were calculated from Eqs. (5) and (6) using optical constants for benzene obtained from an ordinary transmission experiment.il The benzene film was assumed to be isotropic. Of the two absorption lines seen, one belongs to an in-plane vibrational mode, and one to an out-of-plane vibration. Since the electric field of the SEW is primarily perpendicular to the surface, the benzene molecules are clearly not all parallel or all perpendicular to the copper surface. Also it should be noted that the frequencies are the same (within the experimental resolution) as those of solid benzene22 and of nearly the same width. These features indicate that the benzene interacts only weakly with the copper surface, as would be expected for physisorbed molecules. 

The microscopic model, however, cannot take into account net coupling of dynamic dipoles oriented parallel to the surface for the thin (microscopic) film. Such coupling in adsorbed monolayers has been shown [57] by probing an otherwise disallowed transition on a metal through a combination band, to result in a red shift from the singleton frequency. This effect of parallel and normal dipole components can be best exemplified by comparison of the RAIRS spectrum of an isotropic physisorbed molecule with a very strong dipole oscillator, v(C-O) in Mo(CO)6, with the gas phase value (singleton frequency) [58]... 

To evaluate photoisomerization and photo-orientation parameters, and should be known, was calculated from the absorption spectrum of the polymer solution before irradiation, assuming the same extinction coefficient in the film and in solution bq was determined by the Fisher s method, modified by Rau, which holds not only for isotropic but also for anisotropic samples when the isotropic absorbance is considered (vide infra). For this determination, the isotropic absorbance change was recorded versus the irradiating light intensity, and the sample absorbance change was extracted for an irradiation flux extrapolated to infinity for three drbierent combinations of irradiation and analysis wavelengths 488-488, 532-488, and 532-532 nm, irradiation and analysis, respectively. These experiments... 

Altaiskii et al [1] were the first to report on the ESR spectrum of nitrogen donors in Lely grown 3C single crystals. In that study the three-line spectrum is partially resolved. Later work by Carlos et al [2] showed that a well resolved three-line spectrum could be obtained for the CVD films as shown in FIGURE 1. The g-tensor and hyperfine interaction are isotropic with g = 2.0050 and A = 0.11 mT. Both of these parameters are in good agreement with expectations from simple effective-mass-approximation calculations for this polytype [5]. 

The ESR spectra for stretched PTFE films were also measured at room temperature and 77 K. The room temperature spectra obtained at various orientations of the stretch axis to the magnetic field are shown in Fig. 7.28. In addition to a strong signal with large anisotropy, a broad weak signal can be seen at g = 2.016. Since this peak is nearly isotropic and its g value is very close to the g value of the symmetric component of the powder samples, we can again attribute this peak to the peroxy radicals of PTFE. The value of 2.005, which was found with the field parallel to the stretch axis, is very close to g/ = 2.006 obtained for the powder spectrum, while 2.021 measured for the perpendicular direction, is close to gj. = 2.022, This means that the symmetry axis of the g tensor is parallel to the molecular chain axis at room temperature. 

Experimental parameters such as the angle of incidence and film thickness are canceled out if the orientation is calculated from the ratio of the band intensities in the metallic IRRAS of the film and in the transmission (KBr) spectrum of the isotropic bulk sample. For a crystalline-like film, the ratio of the intensities of the VasCH2 and VsCH2 bands (Aas and As, respectively) gives the twist angle directly [604-606] ... 

Nuzzo et al. [509] observed that with increasing temperature from 80 to 400 K, the intensity of the VasCH2 band of alkyl thiol SAMs on Au(lll) decreases while that of the VsCH2 band is almost the same, which was attributed to the intrinsic temperature dependences of these modes. However, this effect can also be due to reducing the film symmetry. As follows from Eqs. (3.50) and (3.52), the AasMg value obtained from the -polarized spectrum of a uniaxial film is the same as for the isotropically distributed film material (if intrinsic spectral perturbations, such as the splitting due to the crystal field effect [504], do not redistribute the intensities). On the other hand, biaxial symmetry should change this ratio. 

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