Angular-dependent studies

Fig. 4. Angular dependent studies for polymer samples in which spectra are studied as a function of election take off angle 0 with respect to the sample surface...

A further dimension may be added by carrying out angular dependent studies. For a homogeneous material, although as we have previously noted toe absolute intensity of a given core level will depend on take off angle because of instrumentally dependent factors, if we look at ratios of intensities for core levels of the same sym-... 

We can now see that an angular dependence study of the quadrupole-split... 

This illustrates the great importance of complementary studies with the differing photon sources as a means of depth profiling particularly for polymer surfaces of sanq)les in powder or fibre form for which routine angular dependent studies are not available. 

One of the most fascinating applications of channeling RBS is the study of lattice locations of impurity atoms. By measuring the angular dependence of the back-scattering yield of the impurity and host atoms around three independent channeling axes it is possible to calculate the position of the impurity. Details can be found elsewhere [3.122]. 

Several other points are worth noticing Well-defined motions lead to well-defined spectra. Thus chain motion can be studied, where the analysis of 2H line shapes yields directly the number of conformations accessible for a given segment. Moreover, even more complicated motions not considered explicitely here lead to spectra, the angular dependence of which can be described by Equation (1 a). The corresponding line shapes can easily be calculated facilitating the analysis of the data. In glassy... 

A theoretical treatment of the effect caused by the competition between the sine-like angular-dependent component of the adsorption potential and dipole lateral interaction demonstrated that the values 6 are the same in the ground state and at the phase transition temperature.81 Study of the structure and dynamics for the CO monolayer adsorbed on the NaCl(lOO) surface using the molecular dynamics method has also led to the inference that angles 0j are practically equalized in a wide temperature range.82 That is why the following consideration of orientational structures and excitations in a system of adsorbed molecules will imply, for the sake of simplicity, the constant value of the inclination angle ty =0(see Fig. 2.14) which is due to the adsorption potential u pj,q>j). 

Important aspects of the interaction of strong laser fields with molecules can be missed in standard TOF experiments, most notably the population of electronically excited states. However, by studying vibrational excitation, the frequency and dephasing of the vibrational motion can be used to identify the electronic state undergoing the vibrational motion. In some cases, this turns out to be a ground state, and in others, an excited state. Once we have identified an excited state, we are left with the question of how and why the state was populated by the strong field. In one example above (the Ij A state discussed in Sect. 1.3.3), the excited state is formed by the removal of an inner orbital electron, in this case a iru electron. This correlates with the measured angular dependence for the ionization to this state. 

The angular dependence of the polarized absorption spectra of LB films containing AMP deposited at lower (20 mN m1) and higher (43 or 50 mN m 1) surface pressures was studied to determine the molecular orientation of porphyrins as schematically shown in Figure 5. No polarization angle (a) dependence was observed at normal incidence. This indicates that the projections of the transition dipole moments of the porphyrins are statistically... 

Single crystal Cu-ENDOR spectra of Cu(acac)2 have been studied by Kita et al.158) up to 100 MHz. The ENDOR transitions of the isotopes 63Cu and 65Cu are found to be well separated for most orientations of Bq. The angular dependence of some Cu-ENDOR frequencies shows pronounced double-minima instead of a single minimum in the region where the hf coupling is smallest. Similar rotation patterns have been observed in Co-ENDOR spectra of Co(acacen) (Fig. 43 b). 

In molecular crystals, the relative importance of the electrostatic, repulsive, and van de Waals interactions is strongly dependent on the nature of the molecule. Nevertheless, in many studies the lattice energy of molecular crystals is simply evaluated with the exp-6 model of Eq. (9.45), which in principle accounts for the van der Waals and repulsive interaction only. As underlined by Desiraju (1989), this formalism may give an approximate description, but it ignores many structure-defining interactions which are electrostatic in nature. The electrostatic interactions have a much more complex angular dependence than the pairwise atom-atom potential functions, and are thus important in defining the structure that actually occurs. 

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