Broida

Bass, A.M. Broida, H.P. In Formation and Trapping of Free Radicals Academic Press New York, 1960. 

Absorption resonances resulting from excitation of surface modes are accompanied by scattering resonances at approximately the same frequencies this was pointed out following (12.26). In most experiments transmission is measured to determine extinction, which is nearly equal to absorption for sufficiently small particles. However, surface mode resonances have been observed in spectra of light scattered at 90° by very small particles of silver, copper, and gold produced by nucleation of vapor in an inert gas stream (Eversole and Broida, 1977). The scattering resonance peak was at 3670 A, near the expected position of the Frohlich mode, for the smallest silver particles. Although peak positions were predictable, differences in widths and shapes of the bands were concluded to be the result of nonsphericity. 

Eversole, J. D., and H. P. Broida, 1977. Size and shape effects in light scattering from small silver, copper, and gold particles, Phys. Rev., B15, 1644-1655. 

Broida and Carrington58 used the 2144-A line of a cadmium discharge to excite selectively the thirteenth rotational level of the first excited vibrational level of the A2H + state. From the emission intensity and eq. (d), quenching efficiencies were computed (Table 3-3). The cadmium arc heated the reactants, the temperature sometimes reaching 550°K. For the computations, an average temperature of 400°K was used. The value found for k% is nearly three times as large as that obtained by Callear and Smith. This high value probably reflects the fact that corrections were not made for the reabsorption of emission. 

Three years later, Broida, Schiff, and Sugden59 took issue with the simple mechanism Kaufman had proposed. They presented experimental evidence, as well as calling attention to previous work, that proved that the radiation was highly structured. They postulated a more elaborate mechanism that involved two excited states of N02 (Fig. 4-7), which, they felt, explained all the data, including those from air afterglow, flames, and fluorescence studies... 

Fig. 4-7. Hypothetical potential energy diagram for N02 potential energy is plotted against r(0—NO) (from Broida, Schiff, and Sugden69 with permission of the Faraday Society).

However, serious doubts have been raised regarding the validity of the Broida, Schiff, and Sugden mechanism by very low-pressure results. Harteck and co-workers3,360 found the intensity of emission to remain second order in the pressure region of 3 to 20 (x. Doherty and Jonathan120 examined the chemiluminescence to pressures as low as 0.85 (x... 

Kaufman243 pointed out that such low values of kM invalidated one of the basic assumptions used by Broida et al. Using values of 2.3 x 104 and 4 x 10 sec-1, respectively, for k63c and k83B, the ratio of radiation from reactions (83C) and (83B) was given by... 

Thus, the radiation from N02 (C) cannot be neglected in comparison with that from N02 (5). Moreover, this objection can be leveled against the mechanism as Broida et al. originally presented it [increasing kBi by a factor of ten would still leave reaction (83C) larger than reaction (83B)]. 

Of course, Broida, Schiff, and Sugden considered the possibility of the radiation from N02 (C) being significant, although they clearly did not favor this contingency. In this case, starting with eq. (k) and making the necessary approximations in the low pressure limit to yield independence of [M], they obtained... 

Fig. V-20. Absorption spectrum of 12 showing the progression ( " = 0) leading to the convergence limit at 4995 A (indicated by the arrow). The transition in this region is Above 6000 A contributions from v" = 1 and 2 become significant. From Capelle and Broida (IS7), reprinted by permission. Copyright 1973 by the American Institute of Physics.

The deuterium tracer experiments of Broida and Gaydon indicated that CH does not come from acetylene itself, a peroxide, or a polymer, so they suggested... 

---