Line width heterogeneous

However, as mentioned above simple lifetime shortening cannot be responsible for the wide lines seen in other molecules. For example, in many fluorescent molecules the observed lifetimes are near the lifetime calculated from Eq. (5), yet the observed width of the optical transitions remain far broader than the natural width. A common dye molecule such as rhodamine 6G has very broad optical absorption bands with widths on the order of 1000 A, but it has a measured radiative lifetime on the order of 10 nsec. Homogeneous lifetime broadening is clearly not the reason that the transitions are broad. The line width of the dye electronic transition must be the result of some combination of heterogeneous environment, coupling to vibrational transitions, and large-scale collective modes. An important goal of some low-temperature studies has been to separate these effects, because each is affected rather differently by temperature. 

In Nafion, two general types of environments were noted. One near 100 ppm is characteristic of an amorphous fluoropolymer environment and the other was attributed to ionic environments. The line width of xenon in the ionic region was very large indicating a very heterogeneous environment... 

Identification of dynamics of a particular molecular fractions with diverse mobility Wider frequency range CP SS-NMR eases interpretation Analysis of NMR line width versus delay time (T profiles) using Gaussian-Lorentzian function (Gaussian part crystalline and Lorentzian amorphous fraction) for partially crystallinity Ambiguity about the source of biphasic spin relaxation decay profile (due to dynamic heterogeneity and/or hetero-nuclear coupling)... 

In the case of transition metal complexes with large g anisotropy in disordered matrices, mw frequencies <9.4 GHz are sometimes preferable, because local heterogeneities (strain) of the matrix lead to a distribution of the principal values of the g- and A-tensors g- and A-strain) and thus to field-dependent line broadening. Such a situation is illustrated in Fig. 11 for Cu(II) in Nation perfluorinated ionomers swollen by acetonitrile the line width of the parallel components was measured at four mw frequencies in the range 1.2-9.4 GHz, and the narrowest line widths were detected for the two low-field lines of the parallel quartet at C band (4.7 GHz) and L band (1.2 GHz). In this way, clear superhyperfine splittings from nuclei were resolved, in addition of course to the hyperfine splittings from Cu(ll). 

Spin probes at the fast motional limit have also been utilized in studies of heterogeneous molecular assembly by HF EPR. Cramer et al. utilized the spin probe TEMPO (2,2,6,6-tetramethylpiperedine-l-oxyl) to investigate poly(butylacrylate) and poly(butylmethacrylate) films. The same spin probe was also used by Smirnov and co-workers to study rotational diffusion of the nitroxide in two phases of aqueous phospholipid dispersions with W-band EPR. Bakker and co-workers utilized another probe - 4-[N,N-dimethyl-lV-(n-hexadecyl)ammonium]-2,2,6,6-tetramethylpiperidinyl-iV-oxyl (HTAB ) to study absorption and aggregation of cetylpyridinium chloride and cetylpyridin-ium salicylate (CPSa) on silica nanoparticles. From W-band line width analysis it was concluded that CPSa on silica surfaces forms two coexisting aggregate phases, one which excludes HTAB and one in which HTAB is concentrated. 

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