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Theoretical Interpretations

The maximum modulation depth, w, = 1, is observed for molecules (such as molecule A) whose fluorescence intensity vanishes completely for certain excitation angles . A fit to the experimental data yields the phase angle and the maximum and minimum fluorescence intensities. From these, the modulation depth w, can be calculated according to Eq. (1). The orientation of the molecular dipole moment Q, is then given by  [Pg.74]

The meaning of Eq. (2) is visualized and summarized in Fig. 4. The orientation of the polarization plane before the sample at the maximum fluorescence which can be directly obtained from the experiments, is plotted versus the location z,-of molecule i (relative to the crystal surface) for different orientations of the transition dipole moment Q, (in steps of 10°). For a chromophore close to the surface Zi 0 or located around z, 8.8 pm, the measured corresponds to the orientation of the transition dipole moment Qj. The birefringence of the crystal regenerates the initial direction of the light polarization after 8.8 pm. [Pg.74]

Let us consider the black trace for a molecule with 2/ = -1-30°, positions and corresponding to the case = Q discussed above. Moving deeper into the crystal (position B) gets smaller than 2, until, at Zi- h. = njl (position B). the max- [Pg.74]

The trapping process has been simulated using Monte Carlo methods based on a rotational isomeric state model 377-379 f j, ydic chains.  [Pg.177]

A tetrafunctional network containing cyclics (heavy lines). Cyclics a and b were trapped by linear chains that passed through them prior to end linking into a network structure. [Pg.178]

Trapping efficiencies for cyclics as a function of cyclic size. [Pg.178]

The trapping process was simulated using a torus centered around each repeat unit in the cyclic.Any empty torus was considered a pathway for a chain of specified diameter to thread and then incarcerate the cyclic once the end-linking process has been completed. Simulations were consistent with experimental trapping efficiencies. It is possible to interpret these experimental results in terms of a power law for the trapping probabilities and fractal cross sections for the PDMS chains. [Pg.179]

It may also be possible to use the trapping technique to prepare networks having no cross links whatsoever. Mixed linear chains, with large amounts of cyclics, are difunctionally end linked to yield an Olympic or chain-mail network (figure 7.30). Such materials are similar in some respects to the catenanes and rotaxanes that have long been of interest to a variety of scientists and mathematicians. Computer simulations could establish the conditions most likely to produce these novel structures. [Pg.179]


A more elaborate theoretical approach develops the concept of surface molecular orbitals and proceeds to evaluate various overlap integrals [119]. Calculations for hydrogen on Pt( 111) planes were consistent with flash desorption and LEED data. In general, the greatly increased availability of LEED structures for chemisorbed films has allowed correspondingly detailed theoretical interpretations, as, for example, of the commonly observed (C2 x 2) structure [120] (note also Ref. 121). [Pg.704]

Pearlstein R M 1991 Theoretical interpretation of antenna pectra Chlorophylls ed H Scheer (Boca Raton, FL CRC) pp 1047-78... [Pg.3031]

The next step towards increasing the accuracy in estimating molecular properties is to use different contributions for atoms in different hybridi2ation states. This simple extension is sufficient to reproduce mean molecular polarizabilities to within 1-3 % of the experimental value. The estimation of mean molecular polarizabilities from atomic refractions has a long history, dating back to around 1911 [7], Miller and Sav-chik were the first to propose a method that considered atom hybridization in which each atom is characterized by its state of atomic hybridization [8]. They derived a formula for calculating these contributions on the basis of a theoretical interpretation of variational perturbation results and on the basis of molecular orbital theory. [Pg.322]

One of the major uses of molecular simulation is to provide useful theoretical interpretation of experimental data. Before the advent of simulation this had to be done by directly comparing experiment with analytical (mathematical) models. The analytical approach has the advantage of simplicity, in that the models are derived from first principles with only a few, if any, adjustable parameters. However, the chemical complexity of biological systems often precludes the direct application of meaningful analytical models or leads to the situation where more than one model can be invoked to explain the same experimental data. [Pg.237]

Another contribution of the potentiostatic technique to s.c.c. studies has been the report that cracking prevails essentially at two potential levels for metals showing an active-passive transition. These potentials are located near the top and bottom of the passive region. Along the same lines, Uhlig and his co-workers have determined critical ranges of potential for s.c.c. , although their theoretical interpretation differs from that of the other references cited. [Pg.1119]

Recalling our earlier discussion of the information-theoretic, interpretation of... [Pg.214]

Innumerable experimental rate measurements of many kinds have been shown to obey the Arrhenius equation (18) or the modified form [k = A T exp (—E/RT)] and, irrespective of any physical significance of the parameters A and E, the approach is an important, established method of reporting and comparing kinetic data. There are, however, grounds for a critical reconsideration for both the methods of application and the theoretical interpretations of observed obedience of experimental data for the reactions of solids to eqn. (18). [Pg.87]

It should be emphasized that whereas the theoretical modelling of An3+ spectra in the condensed phase has reached a high degree of sophistication, the type of modelling of electronic structure of the (IV) and higher-valent actinides discussed here is restricted to very basic interactions and is in an initial state of development. The use of independent experimental methods for establishing the symmetry character of observed transitions is essential to further theoretical interpretation just as it was in the trivalent ion case. [Pg.196]

Mass spectrometric studies yield principally three types of information useful to the radiation chemist the major primary ions one should be concerned with, their reactions with neutral molecules, and thermodynamic information which allows one to eliminate certain reactions on the basis of endothermicity. In addition, attempts at theoretical interpretations of mass spectral fragmentation patterns permit estimates of unimolecular dissociation constants for excited parent ions. [Pg.255]

Reaction Theoretical Interpretation of Quantum Chemical Results. . . 193... [Pg.175]

The most important approximations of the HMO method are, the consideration of only the it-electrons, the neglect of the interaction between them and the neglect of all atom-atom-interactions, if the atoms are not neighbouring. Contrary to the other methods, the molecular geometry does not play a role in the HMO method because only the topologic connection of the atoms in the molecule is considered. In spite of these drastic approximations, the HMO method proved its worth as the first semiempirical procedure with a wide field of applications as well as in the theoretical interpretation of many chemical phenomenons. The method was broadly used in the field of cationic polymerizations in the 60-70 years too (see 2)). [Pg.179]

Various theoretical interpretations of the bias of norboranone 25 have been proposed. Two basic explanations have been suggested, i.e., torsion-based arguments [91] and stereoelectronic arguments [1, 92-95]. [Pg.141]

Changes of activation parameters within a series of related reactions can be used for classification of these series (14, 37, 115). Theoretical interpretation of reactivity should then be somewhat different in each class. In early work, attention was directed to reaction series with constant activation entropy, (34, 35, 38) which were believed to be of prime theoretical significance (16). Later, Blackadder and Hinshelwood distinguished three types (115, 116) ... [Pg.458]

Such conformational dependence presents challenges and an opportunity. The challenges he in properly accounting for its consequences. In many cases, exact conformational energetics and populations in a sample may be unknown, and the nature of the sample inlet may sometimes also mean that a Boltzmann distribution cannot be assumed. Introducing this uncertainty into the data modeling process produces some corresponding uncertainty in the theoretical interpretation of data... [Pg.319]

Ideas concerning the ionic atmosphere can be used for a theoretical interpretation of these phenomena. There are at least two effects associated with the ionic atmosphere, the electrophoretic effect and the relaxation effect, both lowering the ionic mobilities. Formally, this can be written as... [Pg.122]

In many cases the plots are even more complex, and a theoretical interpretation is difficult. Often, the plots of vs. R are evaluated only in a qualitative way, and segments with kinetic semicircles or diffusional straight fines are considered separately. [Pg.214]

Thus, the recombination theory provided the first theoretical interpretation of the linear relation between polarization and the logarithm of current density that had been established experimentally. It is true, though, that the preexponential factor in Eq. (15.12) [2303(RTI2FI) 0.03 V] is four times smaller than the experimental values of slope b but it has been shown in later work that factors closer to the experimental values can be obtained when an inhomogeneous surface is assumed. [Pg.267]

Umsov VS, Dudnikova VB (1998) The trace component trapping effect experimental evidence, theoretical interpretation, and geochemical applications. Geochim Cosmochim Acta 62 1233-1240 Van Orman JA, Grove TL, Shimizu N (1998) Uranium and thorium diffusion in diopside. Earth Planet Sci Lett 160 505-519... [Pg.124]

We outline experimental results and provide theoretical interpretation of effect of adsorption of molecular oxygen and alkyl radicals in condensed media (water, proton-donor and aproton solvents) having different values of dielectric constant on electric conductivity of sensors. We have established that above parameter substantially affects the reversible changes of electric conductivity of a sensor in above media which are rigorously dependent on concentration of dissolved oxygen. [Pg.3]

EDXRF vs. WDXRF, sequential vs. simultaneous XRF), geometry (TXRF, SEXAFS, glancing angle), theoretical interpretations (EXAFS, XANES), microanalysis ( xXRF, EPMA), hyphenation or on-line analysis. There is sufficient scope for polymer/additive analysis by means of XRS tools. [Pg.628]

A theoretical interpretation relating the valence electron concentration and the structure was put forward by H. Jones. If we start from copper and add more and more zinc, the valence electron concentration increases. The added electrons have to occupy higher energy levels, i.e. the energy of the Fermi limit is raised and comes closer to the limits of the first Brillouin zone. This is approached at about VEC = 1.36. Higher values of the VEC require the occupation of antibonding states now the body-centered cubic lattice becomes more favorable as it allows a higher VEC within the first Brillouin zone, up to approximately VEC = 1.48. [Pg.162]

Thus, a suitable refinement of the Debye-Huckel theory must provide a theoretical interpretation of the term CL Originally this term was qualitatively interpreted as a salting-out effect during solvation the ions... [Pg.49]

Max Born (1882-1970 Nobel Prize for physics 1954) laid down the foundation for the further development of quantum theory in 1926 with his statistical interpretation of quantum mechanics. Above all, a theoretical interpretation of the chemical bond was possible. Max Born was one of the most... [Pg.26]


See other pages where Theoretical Interpretations is mentioned: [Pg.226]    [Pg.205]    [Pg.113]    [Pg.176]    [Pg.468]    [Pg.83]    [Pg.49]    [Pg.209]    [Pg.160]    [Pg.6]    [Pg.327]    [Pg.557]    [Pg.101]    [Pg.309]    [Pg.679]    [Pg.385]    [Pg.30]    [Pg.14]    [Pg.40]    [Pg.1199]    [Pg.473]    [Pg.512]    [Pg.192]    [Pg.140]   


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