Measurable extinction

The measured extinction stretch rates for n-decane/ O2/N2 mixtures at 400 K preheat temperature as a function of equivalence ratio are shown in Figure 6.3.3. The flame response curves at varying equivalence ratios are also computed using the kinetic mechanisms of Bikas and Peters (67 species and 354 reactions) [17] and Zhao... 

In an attempt to resolve the discrepancy between calculated and measured extinction coefficients, one can consider the possible contributing factors which follow ... 

On the basis of the above observations it is concluded that at 350 nm the discrepancy between calculated and measured extinction coefficients may be attributed to the additives in the lat-ices and the size disparity of the particles in them. The presence of residual styrene monomer in the particles is strongly suspected. The data are inconclusive in this regard. Whether or not polystyrene latices absorb at 2 h nm can only be established once the contributions to the extinction coefficients from the additives and residual monomer if any, are established. A combination of the aforementioned are probably responsible for departure from theory at 2 k and 280 nm. 

The kinetics of reactions involving the tributylstannyl radical have been refined by laser flash time-resolved UV spectroscopy. The measured extinction coefficient of the BujSn- radical in benzene was 1620 40 M 1cm 1 at 400 nm, the rate constant of the reaction of the /-butoxyl radical with Bu3SnH was (3.5 0.3) x 108M 1 s 1, and the rate constant for the self-reaction of the Bu3Sn radical was (3.6 0.3) x 109 M s1. S29... 

Extinction is determined by measuring the ratio of transmitted to incident irradiance (11.1). Many laboratories are equipped with recording spectrophotometers which can measure this quantity very quickly for liquid or solid samples. In principle this same type of instrument may be used for measuring extinction by particulate samples. The results, however, may be unreliable unless the detector is designed to reject forward-scattered light, which may be the major contributor to extinction by particles larger than the wavelength. 

Figure 11.18 Schematic diagram of an experiment to measure extinction.

Measured extinction spectra for aqueous suspensions of polystyrene spheres—the light scatterer s old friend—are shown in Fig. 11.19. Water is transparent only between about 0.2 and 1.3 jam, which limits measurements to this interval. These curves were obtained with a Cary 14R spectrophotometer, a commonly available double-beam instrument which automatically adjusts for changing light intensity during a wavelength scan and plots a continuous, high-resolution curve of optical density. To reproduce the fine structure faithfully, the curves were traced exactly as they were plotted by the instru-... 

Kigure 11.19 Measured extinction by aqueous suspensions of polystyrene spheres with three different mean diameters. 

Figure 11.20 Measured extinction by five aqueous suspensions of irregular quartz particles (Hodkinson, 1963) at the wavelengths 0.365, 0.436, and 0.546 (im.

Figure 11.22 Schematic diagram of the microwave analog technique for measuring extinction by single oriented particles.

Figure 11.23 Measured extinction of microwave radiation by prolate spheroids. From Greenberg et al. (1961).

Genzel and Martin (1972, 1973) measured extinction by MgO smokes loosely packed on transparent substrates both in air and covered with the transparent oil Nujol. Their results showed absorption bands appreciably shifted from the bulk absorption band the peak frequencies agreed with calculations, but the widths were consistently greater than predicted by sphere theory. In addition, a narrower absorption feature always appeared at the... 

Fig. 17.11 Extinction behavior of strained, opposed-flow, premixed, methane-air flames. The left-hand panel shows the dependence of the maximum temperature at the symmetry plane as a function of the semi-infinite strain-rate parameter a, for five different mixture stoichiometries. The right-hand panel compares measured extinction strain rates [238] with predictions for both the semi-infinite and finite-gap model formulations. The nozzle separation distance is 7 mm (i.e., 3.5 mm from nozzle to symmetry plane).

As, without the use of one of the photo-electric methods, it becomes completely impossible to measure extinction positions of such small parasitic birefringences, the present author relied on an indirect method by the use of revolving windows (217). As pointed out in Section 6.1.5, the windows of the rotor unit were put in a most suitable fixed position. This position is found in the following way ... 

As noted above, the LUT algorithm assumes a unimodal lognormal functional form to describe stratospheric aerosols. This approximation is well suited for most non-volcanic stratospheric aerosols as shown by Pueschel et al. [7] and Yue et al. [8]. Volcanic size distributions, however, are typically bi- or trimodal. This raises the question of whether the assumption of unimodality in the LUT can introduce bias into retrieved values of Rt//, S and V. Russell et al. [1] have shown that retrieved unimodal distributions accurately describe the second, larger mode of several measured bimodal size distributions, but fail to account for the smaller particles in the first mode. The smaller particles, which contribute little to the measured extinction spectra, are not accounted for in the LUT retrievals. Unless this bias is accounted for, the values of Rtff retrieved under the assumption of a unimodal distribution will be overestimated. 

Figure 6. Results of applying the LUT algorithm to synthetic extinction spectra calculated from measured pre- and post-Pinatubo size distributions obtained from Pueschel el al. [9], Goodman el al [10] and Deshler el al. [11,12]. R,/bimodal) is the effective radius of the measured bimodal size distribution, and R /uni modal) is the corresponding effective radius returned by the LUT. The dots are results obtained when a range of distribution widths are considered in the LUT calculations and the crosses are results obtained when at is restricted to the value that yields the best fit between calculated and measured extinction spectra. The solid and dashed curves are second order polynomial fits to the dots and crosses, respectively.

The slow peak was associated with the dissociation channel that produces an H atom and an X(2) fragment, while the fast peak was identified with the channel that produces the I( 3/2) fragment. From the polarization measurements they could obtain the anisotropy parameter 3, and this along with the TOF spectra could be used to derive the branching ratio between the two channels as a function of wavelength. Combining this information with the measured extinction coefficients, they were able to derive the partial extinction coefficients to the upper states that correlate with each of the channels. A modified 6 approximation was then combined with all of this information to calculate the upper repulsive potential curves that lead to dissociation into these products. Four upper states are involved in the dissociation in this region. The symmetries of these four states are 3nx, fjl, 3no, and The first two states produce... 

The results in Table III show that there is a rough parallel between the rates of net electron transfer from Ru(II) to Co (III) and the intensity of the intervalence band observed for the Ru(II)-Ru(III) mixed valence complex. Any such parallelism—more exactly a parallelism between AS+ and the intensities—would imply that a nonadiabatic factor does affect the rates of electron transfer. Unfortunately, it is not possible to examine this relationship in the sensitive region where the reactions are strongly nonadiabatic. The nir bands are very broad, and is difficult to measure extinction coefficients that are less than about 5 M"1 cm-1. 

Crawley et. al. [57] applied the above equations to determine particle size distributions from turbidity measurements. The problems arise in finding a particle size distribution from the measured extinction coefficient due to the ill-defined inversion problem. Scholtz et.al. [58] focused on the problem of analyzing spectra of colloidal solutions, for which the size distribution was known from other methods like electron microscopy and light scattering they termed this transmission spectroscopy. ... 

Total volume is 3.11 ml . 4436 is measured extinction coefficient of guaiacol (tetra-guaiacol is formed) is 25.6/4 cm //imole. 

---