ON THE INTERACTION BETWEEN CUBIC ANHARMONICITY AND A SECOND-ORDER ELECTRIC MOMENT IN THE OPTICAL ABSORPTION OF CRYSTALS

1965 ◽  
pp. 411-419 ◽  
Author(s):  
J.S. LANGER ◽  
A.A. MARADUDIN ◽  
R.F. WALLIS
Keyword(s):  
Optical Absorption ◽  
Second Order ◽  
Electric Moment

Primary Reactions during the Free Anionic Polymerization of β Nitrostyrene

1978 ◽  
Vol 33 (3) ◽  
pp. 253-256 ◽  
Author(s):  
Binh Dinh-Ngoc ◽  
Wolfram Schnabel
Keyword(s):  
Optical Absorption ◽  
Anionic Polymerization ◽  
Radical Anion ◽  
Second Order ◽  
Order Process ◽  
Solvated Electrons ◽  
Rate Laws ◽  
Species Overlap ◽  
Primary Reactions ◽  
Second Order Process

Abstractβ-Nitrostyrene (βNS) was irradiated at r. t. in solutions of hexamethylphosph. triamide (HMPT) with 50 ns pulses of 15 MeV electrons. It was found that βNS reacts with solvated electrons almost encounter controlled (k(e-solv + βNS) = (9 ± 3) · 109 l/mol s) forming the radical anion · βNS-. The optical absorption spectrum of the latter was recorded in dilute solutions ([βNS] < 5 × 10-3 mol/l). At higher βNS concentrations the formation of an additional optical absorption after the pulse in the wavelength range between 460 nm and 570 nm was detected, which is attributed to the reaction of βNS with · βNS- yielding the dimeric radical anion (· βNS-βNS-). The rate constant for this process is 4 × 107 l/mol s. At low βNS concentrations ( < 5 × 10-3 mol/l) the transient spectrum decayed by a second order process (k2 - (2.2 ± 0.5) · 109 l/mol s). This process is correlated to the neutralization of radical anions by cations formed initially. At [βNS] > 5 × 10-3 mol/l only the band at 630 nm decays according to second order kinetics. This band is correlated to the part of the anions with the highest electron density, the nitro groups. At wavelengths below 570 nm the absorptions of various species overlap. These species decay by different rate laws.

Disappearance Voltage Determinations Using a Convergent Beam

1971 ◽  
Vol 29 ◽  
pp. 184-185
Author(s):  
W. L. Bell
Keyword(s):  
Second Order ◽  
Objective Method ◽  
Uniform Thickness ◽  
Rocking Curve ◽  
Crystal Perfection ◽  
Kikuchi Line ◽  
Central Maximum ◽  
Diffraction Patterns ◽  
Convergent Beam ◽  
Beam Technique

Disappearance voltages for second order reflections can be determined experimentally in a variety of ways. The more subjective methods, such as Kikuchi line disappearance and bend contour imaging, involve comparing a series of diffraction patterns or micrographs taken at intervals throughout the disappearance range and selecting that voltage which gives the strongest disappearance effect. The estimated accuracies of these methods are both to within 10 kV, or about 2-4%, of the true disappearance voltage, which is quite sufficient for using these voltages in further calculations. However, it is the necessity of determining this information by comparisons of exposed plates rather than while operating the microscope that detracts from the immediate usefulness of these methods if there is reason to perform experiments at an unknown disappearance voltage.The convergent beam technique for determining the disappearance voltage has been found to be a highly objective method when it is applicable, i.e. when reasonable crystal perfection exists and an area of uniform thickness can be found. The criterion for determining this voltage is that the central maximum disappear from the rocking curve for the second order spot.

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