Effect of Scattered Light

A critical component of any FD or TD experiment should be collection of emission spectra. One possible artifact is illustrated in Hgure 5.11, whidi riiows the emission spectrum of 9,10-diphenylanthracene (DPA) in a solution which also scattered light 9,10-DR was dissdved in ethanol which contained a small amount of Ludox scat-teier. When the mnission was diserved without an emission filter (solid curve in Ingure 5.11), thm was a lai peak due to scattered light at the excitation wavelength of 325 nm. Tbe presence of this scattered component would not be recognized without measurmnent of the emission spectrum and would result in an incorrect intensity decay. 

Fi iieS.IO. Sii x naealUI decays of anthracene (AN) and 9 -wpandvacena (9CA). SMi ea were eqmlibnted with atrao ilieric oxygexL S 9(X2 and 8m = 0.005. From Ref. 68. 

It is possible to correct for background from the sample. The filled circles represent the data corrected according to Eqs. [5.18]-[5.23]. The corrected data can befit to a single decay time with T = 6.01 ns. An alternative iq proach is to fit the data with scattered light to include a second component with a lifetime near zero. This also results in a good fit to the data, with a decay time near zero assodaied with fg - 0.15. However, this procedmt is only appropriate if 

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This paper will be limited to a discussion of our packed column studies in which we have addressed attention to questions regarding, (a) the role of ionic strength and surfactant effects on both HDC and porous packed column behavior, (b) the effects of pore size and pore size distribution on resolution, and (c) the effects of the light scattering characteristics of polystyrene on signal resolution and particle size distribution determination. 

Cabannes factor analy chem An equational factor to correct for the depolarization effect of the horizontal components of scattered light during the determination of molecular weight by optical methods. ko banz. fak-tor cacodyl orgchem (CH3)2As A radical found in, for example, cacodylic acid, (CH3)2A-sOOH. kak-3 dil ... 

Figure 11.28—Effect of light scattering on a spectrum recorded in absorbance and on its derivative spectrum. This figure shows a comparison of the derivative spectra corresponding to the spectrum A of a compound in solution without scattering and to the same spectrum B in the presence of scattering. It can be seen that the effect of scattering is in the order of 10% in absorbance units but only about 1% in the derivative spectrum (modelled spectra).

Flory has recently summarized the experimental evidence pertaining to local correlation and their effects on chain dimensions (49). There is experimental support for local alignment from optical properties such as stress-optical coefficients in networks (both unswelled and swelled in solvents of varying asymmetry), and from the depolarization of scattered light in the undiluted state and at infinite dilution. The results for polymers however, turn out to be not greatly different from those for asymmetric small molecule liquids. The effect of... 

The light leaving the paper should pass through an exit slit to avoid the effect of scatter on the surface of the barrier-layer photocell (Fig. 

The time resolution of the electronics in a single photon counting system can be better than 50 ps. A problem arises because of the inherent dispersion in electron transit times in the photomultiplier used to detect fluorescence, which are typically 0.1—0.5 ns. Although this does not preclude measurements of sub-nanosecond lifetimes, the lifetimes must be deconvoluted from the decay profile by mathematical methods [50, 51]. The effects of the laser pulsewidth and the instrument resolution combine to give an overall system response, L(f). This can be determined experimentally by observing the profile of scattered light from the excitation source. If the true fluorescence profile is given by F(f) then the... 

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