Absorption cross-section maxima and minima in IR absorption bands of small ionic ellipsoidal particles.
Absorption cross-section maxima and minima in IR absorption bands of small ionic ellipsoidal particles.
复制标题
小离子椭圆体颗粒的红外吸收带中吸收截面的最大值和最小值。
作者：
C. Bohren;D. Huffman
在瑞利椭球近似的框架内，可以彻底研究非常小的颗粒的光学吸收截面极值。对于具有由单振荡器洛伦兹模型描述的光学常数的定向椭球，最大吸收的频率位于横向和纵向光学模式频率之间，并且取决于颗粒形状和周围介质;通常，低频峰值高于高频峰值。对于单个椭球体，吸收在频率上的积分与阻尼常数无关。对于随机取向的椭球体，获得了圆盘的积分绝对最大吸收和球体的绝对最小吸收。然而，球体或任何其他椭圆形形状在表面模式被激发的频率下可以是最大的吸收体。在红外光谱中，这种表面模式对于许多常见的绝缘体粒子都是可能的：各种碱金属卤化物、氧化物、碳酸盐和硅酸盐。
Optical absorption cross section extrema can be investigated thoroughly for very small particles within the framework of the Rayleigh ellipsoid approximation. For an oriented ellipsoid with optical constants described by a one-oscillator Lorentz model, the frequency of maximum absorption lies between the transverse and longitudinal optical mode frequencies and depends on the particle shape and the surrounding medium; in general, the low frequency peaks are higher than the high frequency peaks. Absorption integrated over frequency for a single ellipsoid is independent of the damping constant. For randomly oriented ellipsoids, the integrated absolute maximum absorption is obtained for disks and the absolute minimum absorption for spheres. However, a sphere or any other ellipsoidal shape can be the greatest absorber at frequencies where surface modes are excited. Such surface modes are possible in the IR for particles of many common insulators: various alkali halides; oxides; carbonates; and silicates.