Principles of quantitative absorbance measurements in anisotropic crystals
Principles of quantitative absorbance measurements in anisotropic crystals
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DOI：
10.1007/bf00199497
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发表时间：
1996-08-01
影响因子：
1.4
通讯作者：
Rossman, GR
中科院分区：
文献类型：
--
作者：
Libowitzky, E;Rossman, GR
准确测量晶体等各向异性材料的吸光度（A=-log T; T=I/I-0）对于确定所研究的振荡器（吸收体）的浓度和取向非常重要。C . t）。各向异性介质中吸光度的测量更复杂，但它可以从偏振光谱中获得（i）在三个随机的，但正交的晶体部分，或（ii）最好在两个正交的部分，平行于两个轴的指标椭球体取向。为了在不同的晶体类别（包括立方对称性）之间进行比较，将测量的吸光度值转换为一个共同的基础（总吸光度Ai，i）是有用的，其中所有吸收体被校正，就好像它们平行于入射光的E矢量对齐一样。总吸收系数（a（tot）=A（tot）/t）通过（i）a（tot）=Sigma（i=1）（3）（a（max，i）+a（min，i））/2或（ii）a（tot）=a（x）+a（y）+a（z）计算。在非偏振条件下测量吸光率可为各向异性材料的定量研究提供有用的数据.理论方法通过对方解石和黄玉的测量得到证实.根据A（x）/A（tot）=cos（2）（x角吸收体）计算吸收体相对于指示体椭球轴的取向，类似地计算A（y）和A（z）.偏振器的消光比（Pe=I-crossed/I-parallel）对吸收带的振幅有很大的影响，特别是在各向异性吸收很强的情况下。然而，如果Pe是已知的，则根据Amax=-log [（T-max，T-obs-0.5 .佩T-min，T-obs）/（1-0.5 . [1]，与A（min）相似。
The accurate measurement of absorbance (A=-log T; T=I/I-0) in anisotropic materials like crystals is highly important for the determination of the concentration and orientation of the oscillator (absorber) under investigation.The absorbance in isotropic material is linearly dependent on the concentration of the absorber and on the thickness of the sample (A=epsilon . c . t). Measurement of absorbance in anisotropic media is more complicated, but it can be obtained from polarized spectra (i) on three random, but orthogonal sections of a crystal, or (ii) preferably on two orthogonal sections oriented parallel to each of two axes of the indicatrix ellipsoid. To compare among different crystal classes (including cubic symmetry) it is useful to convert measured absorbance values to one common basis (the total absorbance A,,,), wherein all absorbers are corrected as if they were aligned parallel to the E-vector of the incident light. The total absorption coefficient (a(tot)=A(tot)/t) is calculated by(i) a(tot)=Sigma(i=1)(3)(a(max,i)+a(min,i))/2, or by (ii) a(tot)=a(x)+a(y)+a(z).Only in special. circumstances will unpolarized measurements of absorbance provide data useful for quantitative studies of anisotropic material.The theoretical approach is confirmed by measurements on calcite and topaz.The orientation of the absorber with respect to the axes of the indicatrix ellipsoid is calculated according to A(x)/A(tot)=cos(2) (x angle absorber), and analogously for A(y) and A(z). In this way, correct angles are obtained for all cases of symmetry.The extinction ratio of the polarizer (Pe=I-crossed/I-parallel) has considerable influence on the measured amplitude of absorption bands, especially in cases of strong anisotropic absorbance. However, if Pe is known, the true absorbance values can be calculated even with polarizers of low extinction ratio, according to Amax=-log [(T-max,T-obs-0.5 . Pe . T-min,T-obs)/(1-0.5 . Pe)], and similar for A(min).